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* [PATCH v3 0/7] mm: Page fault enhancements
@ 2019-09-11  7:10 Peter Xu
  2019-09-11  7:10 ` [PATCH v3 1/7] mm/gup: Rename "nonblocking" to "locked" where proper Peter Xu
                   ` (6 more replies)
  0 siblings, 7 replies; 12+ messages in thread
From: Peter Xu @ 2019-09-11  7:10 UTC (permalink / raw)
  To: linux-mm, linux-kernel
  Cc: David Hildenbrand, Hugh Dickins, Maya Gokhale, Jerome Glisse,
	Pavel Emelyanov, Johannes Weiner, peterx, Martin Cracauer,
	Marty McFadden, Shaohua Li, Andrea Arcangeli, Mike Kravetz,
	Denis Plotnikov, Mike Rapoport, Linus Torvalds, Mel Gorman,
	Kirill A . Shutemov, Dr . David Alan Gilbert

v3:
- check fatal signals in __get_user_page_locked() [Linus]
- add r-bs

v2:
- resent previous version, rebase only

This series is split out of userfaultfd-wp series to only cover the
general page fault changes, since it seems to make sense itself.

Basically it does two things:

  (a) Allows the page fault handlers to be more interactive on not
      only SIGKILL, but also the rest of userspace signals (especially
      for user-mode faults), and,

  (b) Allows the page fault retry (VM_FAULT_RETRY) to happen for more
      than once.

I'm keeping the CC list as in uffd-wp v5, hopefully I'm not sending
too much spams...

And, instead of writting again the cover letter, I'm just copy-pasting
my previous link here which has more details on why we do this:

  https://patchwork.kernel.org/cover/10691991/

The major change from that latest version should be that we introduced
a new page fault flag FAULT_FLAG_INTERRUPTIBLE as suggested by Linus
[1] to represents that we would like the fault handler to respond to
non-fatal signals.  Also, we're more careful now on when to do the
immediate return of the page fault for such signals.  For example, now
we'll only check against signal_pending() for user-mode page faults
and we keep the kernel-mode page fault patch untouched for it.  More
information can be found in separate patches.

The patchset is only lightly tested on x86.

All comments are greatly welcomed.  Thanks,

[1] https://lkml.org/lkml/2019/6/25/1382

Peter Xu (7):
  mm/gup: Rename "nonblocking" to "locked" where proper
  mm: Introduce FAULT_FLAG_DEFAULT
  mm: Introduce FAULT_FLAG_INTERRUPTIBLE
  mm: Return faster for non-fatal signals in user mode faults
  userfaultfd: Don't retake mmap_sem to emulate NOPAGE
  mm: Allow VM_FAULT_RETRY for multiple times
  mm/gup: Allow VM_FAULT_RETRY for multiple times

 arch/alpha/mm/fault.c           |  7 +--
 arch/arc/mm/fault.c             |  8 +++-
 arch/arm/mm/fault.c             | 14 +++---
 arch/arm64/mm/fault.c           | 16 +++----
 arch/hexagon/mm/vm_fault.c      |  6 +--
 arch/ia64/mm/fault.c            |  6 +--
 arch/m68k/mm/fault.c            | 10 ++--
 arch/microblaze/mm/fault.c      |  6 +--
 arch/mips/mm/fault.c            |  6 +--
 arch/nds32/mm/fault.c           | 12 ++---
 arch/nios2/mm/fault.c           |  8 ++--
 arch/openrisc/mm/fault.c        |  6 +--
 arch/parisc/mm/fault.c          |  9 ++--
 arch/powerpc/mm/fault.c         | 10 ++--
 arch/riscv/mm/fault.c           | 12 ++---
 arch/s390/mm/fault.c            | 11 ++---
 arch/sh/mm/fault.c              |  7 ++-
 arch/sparc/mm/fault_32.c        |  5 +-
 arch/sparc/mm/fault_64.c        |  6 +--
 arch/um/kernel/trap.c           |  7 +--
 arch/unicore32/mm/fault.c       | 11 ++---
 arch/x86/mm/fault.c             |  6 +--
 arch/xtensa/mm/fault.c          |  6 +--
 drivers/gpu/drm/ttm/ttm_bo_vm.c | 12 +++--
 fs/userfaultfd.c                | 28 +-----------
 include/linux/mm.h              | 81 +++++++++++++++++++++++++++++----
 include/linux/sched/signal.h    | 12 +++++
 mm/filemap.c                    |  2 +-
 mm/gup.c                        | 69 ++++++++++++++++------------
 mm/hugetlb.c                    | 14 +++---
 mm/shmem.c                      |  2 +-
 31 files changed, 234 insertions(+), 181 deletions(-)

-- 
2.21.0



^ permalink raw reply	[flat|nested] 12+ messages in thread

* [PATCH v3 1/7] mm/gup: Rename "nonblocking" to "locked" where proper
  2019-09-11  7:10 [PATCH v3 0/7] mm: Page fault enhancements Peter Xu
@ 2019-09-11  7:10 ` Peter Xu
  2019-09-11  7:10 ` [PATCH v3 2/7] mm: Introduce FAULT_FLAG_DEFAULT Peter Xu
                   ` (5 subsequent siblings)
  6 siblings, 0 replies; 12+ messages in thread
From: Peter Xu @ 2019-09-11  7:10 UTC (permalink / raw)
  To: linux-mm, linux-kernel
  Cc: David Hildenbrand, Hugh Dickins, Maya Gokhale, Jerome Glisse,
	Pavel Emelyanov, Johannes Weiner, peterx, Martin Cracauer,
	Marty McFadden, Shaohua Li, Andrea Arcangeli, Mike Kravetz,
	Denis Plotnikov, Mike Rapoport, Linus Torvalds, Mel Gorman,
	Kirill A . Shutemov, Dr . David Alan Gilbert

There's plenty of places around __get_user_pages() that has a parameter
"nonblocking" which does not really mean that "it won't block" (because
it can really block) but instead it shows whether the mmap_sem is
released by up_read() during the page fault handling mostly when
VM_FAULT_RETRY is returned.

We have the correct naming in e.g. get_user_pages_locked() or
get_user_pages_remote() as "locked", however there're still many places
that are using the "nonblocking" as name.

Renaming the places to "locked" where proper to better suite the
functionality of the variable.  While at it, fixing up some of the
comments accordingly.

Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 mm/gup.c     | 44 +++++++++++++++++++++-----------------------
 mm/hugetlb.c |  8 ++++----
 2 files changed, 25 insertions(+), 27 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 98f13ab37bac..eddbb95dcb8f 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -622,12 +622,12 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
 }
 
 /*
- * mmap_sem must be held on entry.  If @nonblocking != NULL and
- * *@flags does not include FOLL_NOWAIT, the mmap_sem may be released.
- * If it is, *@nonblocking will be set to 0 and -EBUSY returned.
+ * mmap_sem must be held on entry.  If @locked != NULL and *@flags
+ * does not include FOLL_NOWAIT, the mmap_sem may be released.  If it
+ * is, *@locked will be set to 0 and -EBUSY returned.
  */
 static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
-		unsigned long address, unsigned int *flags, int *nonblocking)
+		unsigned long address, unsigned int *flags, int *locked)
 {
 	unsigned int fault_flags = 0;
 	vm_fault_t ret;
@@ -639,7 +639,7 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 		fault_flags |= FAULT_FLAG_WRITE;
 	if (*flags & FOLL_REMOTE)
 		fault_flags |= FAULT_FLAG_REMOTE;
-	if (nonblocking)
+	if (locked)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
 	if (*flags & FOLL_NOWAIT)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
@@ -665,8 +665,8 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 	}
 
 	if (ret & VM_FAULT_RETRY) {
-		if (nonblocking && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
-			*nonblocking = 0;
+		if (locked && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
+			*locked = 0;
 		return -EBUSY;
 	}
 
@@ -743,7 +743,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
  *		only intends to ensure the pages are faulted in.
  * @vmas:	array of pointers to vmas corresponding to each page.
  *		Or NULL if the caller does not require them.
- * @nonblocking: whether waiting for disk IO or mmap_sem contention
+ * @locked:     whether we're still with the mmap_sem held
  *
  * Returns number of pages pinned. This may be fewer than the number
  * requested. If nr_pages is 0 or negative, returns 0. If no pages
@@ -772,13 +772,11 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
  * appropriate) must be called after the page is finished with, and
  * before put_page is called.
  *
- * If @nonblocking != NULL, __get_user_pages will not wait for disk IO
- * or mmap_sem contention, and if waiting is needed to pin all pages,
- * *@nonblocking will be set to 0.  Further, if @gup_flags does not
- * include FOLL_NOWAIT, the mmap_sem will be released via up_read() in
- * this case.
+ * If @locked != NULL, *@locked will be set to 0 when mmap_sem is
+ * released by an up_read().  That can happen if @gup_flags does not
+ * have FOLL_NOWAIT.
  *
- * A caller using such a combination of @nonblocking and @gup_flags
+ * A caller using such a combination of @locked and @gup_flags
  * must therefore hold the mmap_sem for reading only, and recognize
  * when it's been released.  Otherwise, it must be held for either
  * reading or writing and will not be released.
@@ -790,7 +788,7 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
 static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 		unsigned long start, unsigned long nr_pages,
 		unsigned int gup_flags, struct page **pages,
-		struct vm_area_struct **vmas, int *nonblocking)
+		struct vm_area_struct **vmas, int *locked)
 {
 	long ret = 0, i = 0;
 	struct vm_area_struct *vma = NULL;
@@ -834,7 +832,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 			if (is_vm_hugetlb_page(vma)) {
 				i = follow_hugetlb_page(mm, vma, pages, vmas,
 						&start, &nr_pages, i,
-						gup_flags, nonblocking);
+						gup_flags, locked);
 				continue;
 			}
 		}
@@ -852,7 +850,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 		page = follow_page_mask(vma, start, foll_flags, &ctx);
 		if (!page) {
 			ret = faultin_page(tsk, vma, start, &foll_flags,
-					nonblocking);
+					   locked);
 			switch (ret) {
 			case 0:
 				goto retry;
@@ -1178,7 +1176,7 @@ EXPORT_SYMBOL(get_user_pages_remote);
  * @vma:   target vma
  * @start: start address
  * @end:   end address
- * @nonblocking:
+ * @locked: whether the mmap_sem is still held
  *
  * This takes care of mlocking the pages too if VM_LOCKED is set.
  *
@@ -1186,14 +1184,14 @@ EXPORT_SYMBOL(get_user_pages_remote);
  *
  * vma->vm_mm->mmap_sem must be held.
  *
- * If @nonblocking is NULL, it may be held for read or write and will
+ * If @locked is NULL, it may be held for read or write and will
  * be unperturbed.
  *
- * If @nonblocking is non-NULL, it must held for read only and may be
- * released.  If it's released, *@nonblocking will be set to 0.
+ * If @locked is non-NULL, it must held for read only and may be
+ * released.  If it's released, *@locked will be set to 0.
  */
 long populate_vma_page_range(struct vm_area_struct *vma,
-		unsigned long start, unsigned long end, int *nonblocking)
+		unsigned long start, unsigned long end, int *locked)
 {
 	struct mm_struct *mm = vma->vm_mm;
 	unsigned long nr_pages = (end - start) / PAGE_SIZE;
@@ -1228,7 +1226,7 @@ long populate_vma_page_range(struct vm_area_struct *vma,
 	 * not result in a stack expansion that recurses back here.
 	 */
 	return __get_user_pages(current, mm, start, nr_pages, gup_flags,
-				NULL, NULL, nonblocking);
+				NULL, NULL, locked);
 }
 
 /*
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index ede7e7f5d1ab..5f816ee42206 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4251,7 +4251,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			 struct page **pages, struct vm_area_struct **vmas,
 			 unsigned long *position, unsigned long *nr_pages,
-			 long i, unsigned int flags, int *nonblocking)
+			 long i, unsigned int flags, int *locked)
 {
 	unsigned long pfn_offset;
 	unsigned long vaddr = *position;
@@ -4322,7 +4322,7 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 				spin_unlock(ptl);
 			if (flags & FOLL_WRITE)
 				fault_flags |= FAULT_FLAG_WRITE;
-			if (nonblocking)
+			if (locked)
 				fault_flags |= FAULT_FLAG_ALLOW_RETRY;
 			if (flags & FOLL_NOWAIT)
 				fault_flags |= FAULT_FLAG_ALLOW_RETRY |
@@ -4339,9 +4339,9 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 				break;
 			}
 			if (ret & VM_FAULT_RETRY) {
-				if (nonblocking &&
+				if (locked &&
 				    !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
-					*nonblocking = 0;
+					*locked = 0;
 				*nr_pages = 0;
 				/*
 				 * VM_FAULT_RETRY must not return an
-- 
2.21.0



^ permalink raw reply	[flat|nested] 12+ messages in thread

* [PATCH v3 2/7] mm: Introduce FAULT_FLAG_DEFAULT
  2019-09-11  7:10 [PATCH v3 0/7] mm: Page fault enhancements Peter Xu
  2019-09-11  7:10 ` [PATCH v3 1/7] mm/gup: Rename "nonblocking" to "locked" where proper Peter Xu
@ 2019-09-11  7:10 ` Peter Xu
  2019-09-11  7:10 ` [PATCH v3 3/7] mm: Introduce FAULT_FLAG_INTERRUPTIBLE Peter Xu
                   ` (4 subsequent siblings)
  6 siblings, 0 replies; 12+ messages in thread
From: Peter Xu @ 2019-09-11  7:10 UTC (permalink / raw)
  To: linux-mm, linux-kernel
  Cc: David Hildenbrand, Hugh Dickins, Maya Gokhale, Jerome Glisse,
	Pavel Emelyanov, Johannes Weiner, peterx, Martin Cracauer,
	Marty McFadden, Shaohua Li, Andrea Arcangeli, Mike Kravetz,
	Denis Plotnikov, Mike Rapoport, Linus Torvalds, Mel Gorman,
	Kirill A . Shutemov, Dr . David Alan Gilbert

Although there're tons of arch-specific page fault handlers, most of
them are still sharing the same initial value of the page fault flags.
Say, merely all of the page fault handlers would allow the fault to be
retried, and they also allow the fault to respond to SIGKILL.

Let's define a default value for the fault flags to replace those
initial page fault flags that were copied over.  With this, it'll be
far easier to introduce new fault flag that can be used by all the
architectures instead of touching all the archs.

Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 arch/alpha/mm/fault.c      | 2 +-
 arch/arc/mm/fault.c        | 2 +-
 arch/arm/mm/fault.c        | 2 +-
 arch/arm64/mm/fault.c      | 2 +-
 arch/hexagon/mm/vm_fault.c | 2 +-
 arch/ia64/mm/fault.c       | 2 +-
 arch/m68k/mm/fault.c       | 2 +-
 arch/microblaze/mm/fault.c | 2 +-
 arch/mips/mm/fault.c       | 2 +-
 arch/nds32/mm/fault.c      | 2 +-
 arch/nios2/mm/fault.c      | 2 +-
 arch/openrisc/mm/fault.c   | 2 +-
 arch/parisc/mm/fault.c     | 2 +-
 arch/powerpc/mm/fault.c    | 2 +-
 arch/riscv/mm/fault.c      | 2 +-
 arch/s390/mm/fault.c       | 2 +-
 arch/sh/mm/fault.c         | 2 +-
 arch/sparc/mm/fault_32.c   | 2 +-
 arch/sparc/mm/fault_64.c   | 2 +-
 arch/um/kernel/trap.c      | 2 +-
 arch/unicore32/mm/fault.c  | 2 +-
 arch/x86/mm/fault.c        | 2 +-
 arch/xtensa/mm/fault.c     | 2 +-
 include/linux/mm.h         | 7 +++++++
 24 files changed, 30 insertions(+), 23 deletions(-)

diff --git a/arch/alpha/mm/fault.c b/arch/alpha/mm/fault.c
index 741e61ef9d3f..de4cc6936391 100644
--- a/arch/alpha/mm/fault.c
+++ b/arch/alpha/mm/fault.c
@@ -89,7 +89,7 @@ do_page_fault(unsigned long address, unsigned long mmcsr,
 	const struct exception_table_entry *fixup;
 	int si_code = SEGV_MAPERR;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	/* As of EV6, a load into $31/$f31 is a prefetch, and never faults
 	   (or is suppressed by the PALcode).  Support that for older CPUs
diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index 3861543b66a0..61919e4e4eec 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -94,7 +94,7 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
 	         (regs->ecr_cause == ECR_C_PROTV_INST_FETCH))
 		exec = 1;
 
-	flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	flags = FAULT_FLAG_DEFAULT;
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
 	if (write)
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 890eeaac3cbb..2ae28ffec622 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -241,7 +241,7 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	struct mm_struct *mm;
 	int sig, code;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	if (kprobe_page_fault(regs, fsr))
 		return 0;
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index cfd65b63f36f..613e7434c208 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -410,7 +410,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 	struct mm_struct *mm = current->mm;
 	vm_fault_t fault, major = 0;
 	unsigned long vm_flags = VM_READ | VM_WRITE;
-	unsigned int mm_flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int mm_flags = FAULT_FLAG_DEFAULT;
 
 	if (kprobe_page_fault(regs, esr))
 		return 0;
diff --git a/arch/hexagon/mm/vm_fault.c b/arch/hexagon/mm/vm_fault.c
index b3bc71680ae4..223787e01bdd 100644
--- a/arch/hexagon/mm/vm_fault.c
+++ b/arch/hexagon/mm/vm_fault.c
@@ -41,7 +41,7 @@ void do_page_fault(unsigned long address, long cause, struct pt_regs *regs)
 	int si_code = SEGV_MAPERR;
 	vm_fault_t fault;
 	const struct exception_table_entry *fixup;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	/*
 	 * If we're in an interrupt or have no user context,
diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c
index c2f299fe9e04..d039b846f671 100644
--- a/arch/ia64/mm/fault.c
+++ b/arch/ia64/mm/fault.c
@@ -65,7 +65,7 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re
 	struct mm_struct *mm = current->mm;
 	unsigned long mask;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	mask = ((((isr >> IA64_ISR_X_BIT) & 1UL) << VM_EXEC_BIT)
 		| (((isr >> IA64_ISR_W_BIT) & 1UL) << VM_WRITE_BIT));
diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
index e9b1d7585b43..8e734309ace9 100644
--- a/arch/m68k/mm/fault.c
+++ b/arch/m68k/mm/fault.c
@@ -71,7 +71,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct * vma;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	pr_debug("do page fault:\nregs->sr=%#x, regs->pc=%#lx, address=%#lx, %ld, %p\n",
 		regs->sr, regs->pc, address, error_code, mm ? mm->pgd : NULL);
diff --git a/arch/microblaze/mm/fault.c b/arch/microblaze/mm/fault.c
index e6a810b0c7ad..45c9f66c1dbc 100644
--- a/arch/microblaze/mm/fault.c
+++ b/arch/microblaze/mm/fault.c
@@ -91,7 +91,7 @@ void do_page_fault(struct pt_regs *regs, unsigned long address,
 	int code = SEGV_MAPERR;
 	int is_write = error_code & ESR_S;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	regs->ear = address;
 	regs->esr = error_code;
diff --git a/arch/mips/mm/fault.c b/arch/mips/mm/fault.c
index f589aa8f47d9..6660b77ff8f3 100644
--- a/arch/mips/mm/fault.c
+++ b/arch/mips/mm/fault.c
@@ -44,7 +44,7 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
 	const int field = sizeof(unsigned long) * 2;
 	int si_code;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	static DEFINE_RATELIMIT_STATE(ratelimit_state, 5 * HZ, 10);
 
diff --git a/arch/nds32/mm/fault.c b/arch/nds32/mm/fault.c
index 064ae5d2159d..a40de112a23a 100644
--- a/arch/nds32/mm/fault.c
+++ b/arch/nds32/mm/fault.c
@@ -76,7 +76,7 @@ void do_page_fault(unsigned long entry, unsigned long addr,
 	int si_code;
 	vm_fault_t fault;
 	unsigned int mask = VM_READ | VM_WRITE | VM_EXEC;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	error_code = error_code & (ITYPE_mskINST | ITYPE_mskETYPE);
 	tsk = current;
diff --git a/arch/nios2/mm/fault.c b/arch/nios2/mm/fault.c
index 6a2e716b959f..a401b45cae47 100644
--- a/arch/nios2/mm/fault.c
+++ b/arch/nios2/mm/fault.c
@@ -47,7 +47,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause,
 	struct mm_struct *mm = tsk->mm;
 	int code = SEGV_MAPERR;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	cause >>= 2;
 
diff --git a/arch/openrisc/mm/fault.c b/arch/openrisc/mm/fault.c
index 5d4d3a9691d0..fd1592a56238 100644
--- a/arch/openrisc/mm/fault.c
+++ b/arch/openrisc/mm/fault.c
@@ -50,7 +50,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,
 	struct vm_area_struct *vma;
 	int si_code;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	tsk = current;
 
diff --git a/arch/parisc/mm/fault.c b/arch/parisc/mm/fault.c
index adbd5e2144a3..355e3e13fa72 100644
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -274,7 +274,7 @@ void do_page_fault(struct pt_regs *regs, unsigned long code,
 	if (!mm)
 		goto no_context;
 
-	flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	flags = FAULT_FLAG_DEFAULT;
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
 
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 8432c281de92..408ee769c470 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -435,7 +435,7 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 {
 	struct vm_area_struct * vma;
 	struct mm_struct *mm = current->mm;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
  	int is_exec = TRAP(regs) == 0x400;
 	int is_user = user_mode(regs);
 	int is_write = page_fault_is_write(error_code);
diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index 96add1427a75..deeb820bd855 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -28,7 +28,7 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 	struct vm_area_struct *vma;
 	struct mm_struct *mm;
 	unsigned long addr, cause;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 	int code = SEGV_MAPERR;
 	vm_fault_t fault;
 
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 7b0bb475c166..74a77b2bca75 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -429,7 +429,7 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 
 	address = trans_exc_code & __FAIL_ADDR_MASK;
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
-	flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	flags = FAULT_FLAG_DEFAULT;
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
 	if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
diff --git a/arch/sh/mm/fault.c b/arch/sh/mm/fault.c
index 5f51456f4fc7..becf0be267bb 100644
--- a/arch/sh/mm/fault.c
+++ b/arch/sh/mm/fault.c
@@ -380,7 +380,7 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
 	struct mm_struct *mm;
 	struct vm_area_struct * vma;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	tsk = current;
 	mm = tsk->mm;
diff --git a/arch/sparc/mm/fault_32.c b/arch/sparc/mm/fault_32.c
index 8d69de111470..0863f6fdd2c5 100644
--- a/arch/sparc/mm/fault_32.c
+++ b/arch/sparc/mm/fault_32.c
@@ -168,7 +168,7 @@ asmlinkage void do_sparc_fault(struct pt_regs *regs, int text_fault, int write,
 	int from_user = !(regs->psr & PSR_PS);
 	int code;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	if (text_fault)
 		address = regs->pc;
diff --git a/arch/sparc/mm/fault_64.c b/arch/sparc/mm/fault_64.c
index 2371fb6b97e4..a1cba3eef79e 100644
--- a/arch/sparc/mm/fault_64.c
+++ b/arch/sparc/mm/fault_64.c
@@ -267,7 +267,7 @@ asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
 	int si_code, fault_code;
 	vm_fault_t fault;
 	unsigned long address, mm_rss;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	fault_code = get_thread_fault_code();
 
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index 58fe36856182..bc2756782d64 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -32,7 +32,7 @@ int handle_page_fault(unsigned long address, unsigned long ip,
 	pmd_t *pmd;
 	pte_t *pte;
 	int err = -EFAULT;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	*code_out = SEGV_MAPERR;
 
diff --git a/arch/unicore32/mm/fault.c b/arch/unicore32/mm/fault.c
index 76342de9cf8c..60453c892c51 100644
--- a/arch/unicore32/mm/fault.c
+++ b/arch/unicore32/mm/fault.c
@@ -202,7 +202,7 @@ static int do_pf(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 	struct mm_struct *mm;
 	int sig, code;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	tsk = current;
 	mm = tsk->mm;
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 9ceacd1156db..994c860ac2d8 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1287,7 +1287,7 @@ void do_user_addr_fault(struct pt_regs *regs,
 	struct task_struct *tsk;
 	struct mm_struct *mm;
 	vm_fault_t fault, major = 0;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	tsk = current;
 	mm = tsk->mm;
diff --git a/arch/xtensa/mm/fault.c b/arch/xtensa/mm/fault.c
index f81b1478da61..d2b082908538 100644
--- a/arch/xtensa/mm/fault.c
+++ b/arch/xtensa/mm/fault.c
@@ -43,7 +43,7 @@ void do_page_fault(struct pt_regs *regs)
 
 	int is_write, is_exec;
 	vm_fault_t fault;
-	unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
 
 	code = SEGV_MAPERR;
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0334ca97c584..57fb5c535f8e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -393,6 +393,13 @@ extern pgprot_t protection_map[16];
 #define FAULT_FLAG_REMOTE	0x80	/* faulting for non current tsk/mm */
 #define FAULT_FLAG_INSTRUCTION  0x100	/* The fault was during an instruction fetch */
 
+/*
+ * The default fault flags that should be used by most of the
+ * arch-specific page fault handlers.
+ */
+#define FAULT_FLAG_DEFAULT  (FAULT_FLAG_ALLOW_RETRY | \
+			     FAULT_FLAG_KILLABLE)
+
 #define FAULT_FLAG_TRACE \
 	{ FAULT_FLAG_WRITE,		"WRITE" }, \
 	{ FAULT_FLAG_MKWRITE,		"MKWRITE" }, \
-- 
2.21.0



^ permalink raw reply	[flat|nested] 12+ messages in thread

* [PATCH v3 3/7] mm: Introduce FAULT_FLAG_INTERRUPTIBLE
  2019-09-11  7:10 [PATCH v3 0/7] mm: Page fault enhancements Peter Xu
  2019-09-11  7:10 ` [PATCH v3 1/7] mm/gup: Rename "nonblocking" to "locked" where proper Peter Xu
  2019-09-11  7:10 ` [PATCH v3 2/7] mm: Introduce FAULT_FLAG_DEFAULT Peter Xu
@ 2019-09-11  7:10 ` Peter Xu
  2019-09-11 10:15   ` David Hildenbrand
  2019-09-11  7:10 ` [PATCH v3 4/7] mm: Return faster for non-fatal signals in user mode faults Peter Xu
                   ` (3 subsequent siblings)
  6 siblings, 1 reply; 12+ messages in thread
From: Peter Xu @ 2019-09-11  7:10 UTC (permalink / raw)
  To: linux-mm, linux-kernel
  Cc: David Hildenbrand, Hugh Dickins, Maya Gokhale, Jerome Glisse,
	Pavel Emelyanov, Johannes Weiner, peterx, Martin Cracauer,
	Marty McFadden, Shaohua Li, Andrea Arcangeli, Mike Kravetz,
	Denis Plotnikov, Mike Rapoport, Linus Torvalds, Mel Gorman,
	Kirill A . Shutemov, Dr . David Alan Gilbert

handle_userfaultfd() is currently the only one place in the kernel
page fault procedures that can respond to non-fatal userspace signals.
It was trying to detect such an allowance by checking against USER &
KILLABLE flags, which was "un-official".

In this patch, we introduced a new flag (FAULT_FLAG_INTERRUPTIBLE) to
show that the fault handler allows the fault procedure to respond even
to non-fatal signals.  Meanwhile, add this new flag to the default
fault flags so that all the page fault handlers can benefit from the
new flag.  With that, replacing the userfault check to this one.

Since the line is getting even longer, clean up the fault flags a bit
too to ease TTY users.

Although we've got a new flag and applied it, we shouldn't have any
functional change with this patch so far.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 fs/userfaultfd.c   |  4 +---
 include/linux/mm.h | 39 ++++++++++++++++++++++++++++-----------
 2 files changed, 29 insertions(+), 14 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index ccbdbd62f0d8..4a8ad2dc2b6f 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -462,9 +462,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 	uwq.ctx = ctx;
 	uwq.waken = false;
 
-	return_to_userland =
-		(vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
-		(FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
+	return_to_userland = vmf->flags & FAULT_FLAG_INTERRUPTIBLE;
 	blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
 			 TASK_KILLABLE;
 
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 57fb5c535f8e..53ec7abb8472 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -383,22 +383,38 @@ extern unsigned int kobjsize(const void *objp);
  */
 extern pgprot_t protection_map[16];
 
-#define FAULT_FLAG_WRITE	0x01	/* Fault was a write access */
-#define FAULT_FLAG_MKWRITE	0x02	/* Fault was mkwrite of existing pte */
-#define FAULT_FLAG_ALLOW_RETRY	0x04	/* Retry fault if blocking */
-#define FAULT_FLAG_RETRY_NOWAIT	0x08	/* Don't drop mmap_sem and wait when retrying */
-#define FAULT_FLAG_KILLABLE	0x10	/* The fault task is in SIGKILL killable region */
-#define FAULT_FLAG_TRIED	0x20	/* Second try */
-#define FAULT_FLAG_USER		0x40	/* The fault originated in userspace */
-#define FAULT_FLAG_REMOTE	0x80	/* faulting for non current tsk/mm */
-#define FAULT_FLAG_INSTRUCTION  0x100	/* The fault was during an instruction fetch */
+/**
+ * Fault flag definitions.
+ *
+ * @FAULT_FLAG_WRITE: Fault was a write fault.
+ * @FAULT_FLAG_MKWRITE: Fault was mkwrite of existing PTE.
+ * @FAULT_FLAG_ALLOW_RETRY: Allow to retry the fault if blocked.
+ * @FAULT_FLAG_RETRY_NOWAIT: Don't drop mmap_sem and wait when retrying.
+ * @FAULT_FLAG_KILLABLE: The fault task is in SIGKILL killable region.
+ * @FAULT_FLAG_TRIED: The fault has been tried once.
+ * @FAULT_FLAG_USER: The fault originated in userspace.
+ * @FAULT_FLAG_REMOTE: The fault is not for current task/mm.
+ * @FAULT_FLAG_INSTRUCTION: The fault was during an instruction fetch.
+ * @FAULT_FLAG_INTERRUPTIBLE: The fault can be interrupted by non-fatal signals.
+ */
+#define FAULT_FLAG_WRITE			0x01
+#define FAULT_FLAG_MKWRITE			0x02
+#define FAULT_FLAG_ALLOW_RETRY			0x04
+#define FAULT_FLAG_RETRY_NOWAIT			0x08
+#define FAULT_FLAG_KILLABLE			0x10
+#define FAULT_FLAG_TRIED			0x20
+#define FAULT_FLAG_USER				0x40
+#define FAULT_FLAG_REMOTE			0x80
+#define FAULT_FLAG_INSTRUCTION  		0x100
+#define FAULT_FLAG_INTERRUPTIBLE		0x200
 
 /*
  * The default fault flags that should be used by most of the
  * arch-specific page fault handlers.
  */
 #define FAULT_FLAG_DEFAULT  (FAULT_FLAG_ALLOW_RETRY | \
-			     FAULT_FLAG_KILLABLE)
+			     FAULT_FLAG_KILLABLE | \
+			     FAULT_FLAG_INTERRUPTIBLE)
 
 #define FAULT_FLAG_TRACE \
 	{ FAULT_FLAG_WRITE,		"WRITE" }, \
@@ -409,7 +425,8 @@ extern pgprot_t protection_map[16];
 	{ FAULT_FLAG_TRIED,		"TRIED" }, \
 	{ FAULT_FLAG_USER,		"USER" }, \
 	{ FAULT_FLAG_REMOTE,		"REMOTE" }, \
-	{ FAULT_FLAG_INSTRUCTION,	"INSTRUCTION" }
+	{ FAULT_FLAG_INSTRUCTION,	"INSTRUCTION" }, \
+	{ FAULT_FLAG_INTERRUPTIBLE,	"INTERRUPTIBLE" }
 
 /*
  * vm_fault is filled by the the pagefault handler and passed to the vma's
-- 
2.21.0



^ permalink raw reply	[flat|nested] 12+ messages in thread

* [PATCH v3 4/7] mm: Return faster for non-fatal signals in user mode faults
  2019-09-11  7:10 [PATCH v3 0/7] mm: Page fault enhancements Peter Xu
                   ` (2 preceding siblings ...)
  2019-09-11  7:10 ` [PATCH v3 3/7] mm: Introduce FAULT_FLAG_INTERRUPTIBLE Peter Xu
@ 2019-09-11  7:10 ` Peter Xu
  2019-09-11  7:10 ` [PATCH v3 5/7] userfaultfd: Don't retake mmap_sem to emulate NOPAGE Peter Xu
                   ` (2 subsequent siblings)
  6 siblings, 0 replies; 12+ messages in thread
From: Peter Xu @ 2019-09-11  7:10 UTC (permalink / raw)
  To: linux-mm, linux-kernel
  Cc: David Hildenbrand, Hugh Dickins, Maya Gokhale, Jerome Glisse,
	Pavel Emelyanov, Johannes Weiner, peterx, Martin Cracauer,
	Marty McFadden, Shaohua Li, Andrea Arcangeli, Mike Kravetz,
	Denis Plotnikov, Mike Rapoport, Linus Torvalds, Mel Gorman,
	Kirill A . Shutemov, Dr . David Alan Gilbert

The idea comes from the upstream discussion between Linus and Andrea:

  https://lkml.org/lkml/2017/10/30/560

A summary to the issue: there was a special path in handle_userfault()
in the past that we'll return a VM_FAULT_NOPAGE when we detected
non-fatal signals when waiting for userfault handling.  We did that by
reacquiring the mmap_sem before returning.  However that brings a risk
in that the vmas might have changed when we retake the mmap_sem and
even we could be holding an invalid vma structure.

This patch is a preparation of removing that special path by allowing
the page fault to return even faster if we were interrupted by a
non-fatal signal during a user-mode page fault handling routine.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 arch/alpha/mm/fault.c        |  3 ++-
 arch/arc/mm/fault.c          |  5 +++++
 arch/arm/mm/fault.c          |  9 +++++----
 arch/arm64/mm/fault.c        |  9 +++++----
 arch/hexagon/mm/vm_fault.c   |  3 ++-
 arch/ia64/mm/fault.c         |  3 ++-
 arch/m68k/mm/fault.c         |  5 +++--
 arch/microblaze/mm/fault.c   |  3 ++-
 arch/mips/mm/fault.c         |  3 ++-
 arch/nds32/mm/fault.c        |  9 +++++----
 arch/nios2/mm/fault.c        |  3 ++-
 arch/openrisc/mm/fault.c     |  3 ++-
 arch/parisc/mm/fault.c       |  3 ++-
 arch/powerpc/mm/fault.c      |  2 ++
 arch/riscv/mm/fault.c        |  5 +++--
 arch/s390/mm/fault.c         |  4 ++--
 arch/sh/mm/fault.c           |  4 ++++
 arch/sparc/mm/fault_32.c     |  2 +-
 arch/sparc/mm/fault_64.c     |  3 ++-
 arch/um/kernel/trap.c        |  4 +++-
 arch/unicore32/mm/fault.c    |  5 +++--
 arch/x86/mm/fault.c          |  2 ++
 arch/xtensa/mm/fault.c       |  3 ++-
 include/linux/sched/signal.h | 12 ++++++++++++
 24 files changed, 75 insertions(+), 32 deletions(-)

diff --git a/arch/alpha/mm/fault.c b/arch/alpha/mm/fault.c
index de4cc6936391..ab1d4212d658 100644
--- a/arch/alpha/mm/fault.c
+++ b/arch/alpha/mm/fault.c
@@ -150,7 +150,8 @@ do_page_fault(unsigned long address, unsigned long mmcsr,
 	   the fault.  */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs)))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index 61919e4e4eec..27adf4e608e4 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -142,6 +142,11 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
 				goto no_context;
 			return;
 		}
+
+		/* Allow user to handle non-fatal signals first */
+		if (signal_pending(current) && user_mode(regs))
+			return;
+
 		/*
 		 * retry state machine
 		 */
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 2ae28ffec622..f00fb4eafe54 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -291,14 +291,15 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 
 	fault = __do_page_fault(mm, addr, fsr, flags, tsk);
 
-	/* If we need to retry but a fatal signal is pending, handle the
+	/* If we need to retry but a signal is pending, try to handle the
 	 * signal first. We do not need to release the mmap_sem because
 	 * it would already be released in __lock_page_or_retry in
 	 * mm/filemap.c. */
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
-		if (!user_mode(regs))
+	if (unlikely(fault & VM_FAULT_RETRY && signal_pending(current))) {
+		if (fatal_signal_pending(current) && !user_mode(regs))
 			goto no_context;
-		return 0;
+		if (user_mode(regs))
+			return 0;
 	}
 
 	/*
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 613e7434c208..0d3fe0ea6a70 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -479,15 +479,16 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 
 	if (fault & VM_FAULT_RETRY) {
 		/*
-		 * If we need to retry but a fatal signal is pending,
+		 * If we need to retry but a signal is pending, try to
 		 * handle the signal first. We do not need to release
 		 * the mmap_sem because it would already be released
 		 * in __lock_page_or_retry in mm/filemap.c.
 		 */
-		if (fatal_signal_pending(current)) {
-			if (!user_mode(regs))
+		if (signal_pending(current)) {
+			if (fatal_signal_pending(current) && !user_mode(regs))
 				goto no_context;
-			return 0;
+			if (user_mode(regs))
+				return 0;
 		}
 
 		/*
diff --git a/arch/hexagon/mm/vm_fault.c b/arch/hexagon/mm/vm_fault.c
index 223787e01bdd..88a2e5635bfb 100644
--- a/arch/hexagon/mm/vm_fault.c
+++ b/arch/hexagon/mm/vm_fault.c
@@ -91,7 +91,8 @@ void do_page_fault(unsigned long address, long cause, struct pt_regs *regs)
 
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs)))
 		return;
 
 	/* The most common case -- we are done. */
diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c
index d039b846f671..8d47acf50fda 100644
--- a/arch/ia64/mm/fault.c
+++ b/arch/ia64/mm/fault.c
@@ -141,7 +141,8 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re
 	 */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs)))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
index 8e734309ace9..103f93ba8139 100644
--- a/arch/m68k/mm/fault.c
+++ b/arch/m68k/mm/fault.c
@@ -138,8 +138,9 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
 	fault = handle_mm_fault(vma, address, flags);
 	pr_debug("handle_mm_fault returns %x\n", fault);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
-		return 0;
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs)))
+		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
 		if (fault & VM_FAULT_OOM)
diff --git a/arch/microblaze/mm/fault.c b/arch/microblaze/mm/fault.c
index 45c9f66c1dbc..8b0615eab4b6 100644
--- a/arch/microblaze/mm/fault.c
+++ b/arch/microblaze/mm/fault.c
@@ -217,7 +217,8 @@ void do_page_fault(struct pt_regs *regs, unsigned long address,
 	 */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs)))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/mips/mm/fault.c b/arch/mips/mm/fault.c
index 6660b77ff8f3..48aac20a1ded 100644
--- a/arch/mips/mm/fault.c
+++ b/arch/mips/mm/fault.c
@@ -154,7 +154,8 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
 	 */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs)))
 		return;
 
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
diff --git a/arch/nds32/mm/fault.c b/arch/nds32/mm/fault.c
index a40de112a23a..baa44f9d0b4a 100644
--- a/arch/nds32/mm/fault.c
+++ b/arch/nds32/mm/fault.c
@@ -206,14 +206,15 @@ void do_page_fault(unsigned long entry, unsigned long addr,
 	fault = handle_mm_fault(vma, addr, flags);
 
 	/*
-	 * If we need to retry but a fatal signal is pending, handle the
+	 * If we need to retry but a signal is pending, try to handle the
 	 * signal first. We do not need to release the mmap_sem because it
 	 * would already be released in __lock_page_or_retry in mm/filemap.c.
 	 */
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
-		if (!user_mode(regs))
+	if ((fault & VM_FAULT_RETRY) && signal_pending(current)) {
+		if (fatal_signal_pending(current) && !user_mode(regs))
 			goto no_context;
-		return;
+		if (user_mode(regs))
+			return;
 	}
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/nios2/mm/fault.c b/arch/nios2/mm/fault.c
index a401b45cae47..f9f178484184 100644
--- a/arch/nios2/mm/fault.c
+++ b/arch/nios2/mm/fault.c
@@ -133,7 +133,8 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause,
 	 */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs)))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/openrisc/mm/fault.c b/arch/openrisc/mm/fault.c
index fd1592a56238..8ba3696dd10c 100644
--- a/arch/openrisc/mm/fault.c
+++ b/arch/openrisc/mm/fault.c
@@ -161,7 +161,8 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,
 
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs)))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/parisc/mm/fault.c b/arch/parisc/mm/fault.c
index 355e3e13fa72..163dcb080c7b 100644
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -304,7 +304,8 @@ void do_page_fault(struct pt_regs *regs, unsigned long code,
 
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs)))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 408ee769c470..d321a6c5fe62 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -596,6 +596,8 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 			 */
 			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
+			if (is_user && signal_pending(current))
+				return 0;
 			if (!fatal_signal_pending(current))
 				goto retry;
 		}
diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index deeb820bd855..ea8f301de65b 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -111,11 +111,12 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 	fault = handle_mm_fault(vma, addr, flags);
 
 	/*
-	 * If we need to retry but a fatal signal is pending, handle the
+	 * If we need to retry but a signal is pending, try to handle the
 	 * signal first. We do not need to release the mmap_sem because it
 	 * would already be released in __lock_page_or_retry in mm/filemap.c.
 	 */
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(tsk))
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs)))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 74a77b2bca75..3ad77501deef 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -480,8 +480,8 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 	 * the fault.
 	 */
 	fault = handle_mm_fault(vma, address, flags);
-	/* No reason to continue if interrupted by SIGKILL. */
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs))) {
 		fault = VM_FAULT_SIGNAL;
 		if (flags & FAULT_FLAG_RETRY_NOWAIT)
 			goto out_up;
diff --git a/arch/sh/mm/fault.c b/arch/sh/mm/fault.c
index becf0be267bb..f620282a37fd 100644
--- a/arch/sh/mm/fault.c
+++ b/arch/sh/mm/fault.c
@@ -489,6 +489,10 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
 			 * have already released it in __lock_page_or_retry
 			 * in mm/filemap.c.
 			 */
+
+			if (user_mode(regs) && signal_pending(tsk))
+				return;
+
 			goto retry;
 		}
 	}
diff --git a/arch/sparc/mm/fault_32.c b/arch/sparc/mm/fault_32.c
index 0863f6fdd2c5..9af0c3ad50d6 100644
--- a/arch/sparc/mm/fault_32.c
+++ b/arch/sparc/mm/fault_32.c
@@ -237,7 +237,7 @@ asmlinkage void do_sparc_fault(struct pt_regs *regs, int text_fault, int write,
 	 */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) && fault_should_check_signal(from_user))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/sparc/mm/fault_64.c b/arch/sparc/mm/fault_64.c
index a1cba3eef79e..566f05f9040b 100644
--- a/arch/sparc/mm/fault_64.c
+++ b/arch/sparc/mm/fault_64.c
@@ -421,7 +421,8 @@ asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
 
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(flags & FAULT_FLAG_USER))
 		goto exit_exception;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index bc2756782d64..3c72111f27e9 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -76,7 +76,9 @@ int handle_page_fault(unsigned long address, unsigned long ip,
 
 		fault = handle_mm_fault(vma, address, flags);
 
-		if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+
+		if ((fault & VM_FAULT_RETRY) &&
+		    fault_should_check_signal(is_user))
 			goto out_nosemaphore;
 
 		if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/arch/unicore32/mm/fault.c b/arch/unicore32/mm/fault.c
index 60453c892c51..04c193439c97 100644
--- a/arch/unicore32/mm/fault.c
+++ b/arch/unicore32/mm/fault.c
@@ -246,11 +246,12 @@ static int do_pf(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 
 	fault = __do_pf(mm, addr, fsr, flags, tsk);
 
-	/* If we need to retry but a fatal signal is pending, handle the
+	/* If we need to retry but a signal is pending, try to handle the
 	 * signal first. We do not need to release the mmap_sem because
 	 * it would already be released in __lock_page_or_retry in
 	 * mm/filemap.c. */
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs)))
 		return 0;
 
 	if (!(fault & VM_FAULT_ERROR) && (flags & FAULT_FLAG_ALLOW_RETRY)) {
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 994c860ac2d8..f7836472961e 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1451,6 +1451,8 @@ void do_user_addr_fault(struct pt_regs *regs,
 		if (flags & FAULT_FLAG_ALLOW_RETRY) {
 			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
+			if ((flags & FAULT_FLAG_USER) && signal_pending(tsk))
+				return;
 			if (!fatal_signal_pending(tsk))
 				goto retry;
 		}
diff --git a/arch/xtensa/mm/fault.c b/arch/xtensa/mm/fault.c
index d2b082908538..094606676c36 100644
--- a/arch/xtensa/mm/fault.c
+++ b/arch/xtensa/mm/fault.c
@@ -110,7 +110,8 @@ void do_page_fault(struct pt_regs *regs)
 	 */
 	fault = handle_mm_fault(vma, address, flags);
 
-	if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+	if ((fault & VM_FAULT_RETRY) &&
+	    fault_should_check_signal(user_mode(regs)))
 		return;
 
 	if (unlikely(fault & VM_FAULT_ERROR)) {
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index efd8ce7675ed..ccce63f2822d 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -377,6 +377,18 @@ static inline int signal_pending_state(long state, struct task_struct *p)
 	return (state & TASK_INTERRUPTIBLE) || __fatal_signal_pending(p);
 }
 
+/*
+ * This should only be used in fault handlers to decide whether we
+ * should stop the current fault routine to handle the signals
+ * instead.  It should normally be used when a signal interrupted a
+ * page fault which can lead to a VM_FAULT_RETRY.
+ */
+static inline bool fault_should_check_signal(bool is_user)
+{
+	return (fatal_signal_pending(current) ||
+		(is_user && signal_pending(current)));
+}
+
 /*
  * Reevaluate whether the task has signals pending delivery.
  * Wake the task if so.
-- 
2.21.0



^ permalink raw reply	[flat|nested] 12+ messages in thread

* [PATCH v3 5/7] userfaultfd: Don't retake mmap_sem to emulate NOPAGE
  2019-09-11  7:10 [PATCH v3 0/7] mm: Page fault enhancements Peter Xu
                   ` (3 preceding siblings ...)
  2019-09-11  7:10 ` [PATCH v3 4/7] mm: Return faster for non-fatal signals in user mode faults Peter Xu
@ 2019-09-11  7:10 ` Peter Xu
  2019-09-11  7:10 ` [PATCH v3 6/7] mm: Allow VM_FAULT_RETRY for multiple times Peter Xu
  2019-09-11  7:10 ` [PATCH v3 7/7] mm/gup: " Peter Xu
  6 siblings, 0 replies; 12+ messages in thread
From: Peter Xu @ 2019-09-11  7:10 UTC (permalink / raw)
  To: linux-mm, linux-kernel
  Cc: David Hildenbrand, Hugh Dickins, Maya Gokhale, Jerome Glisse,
	Pavel Emelyanov, Johannes Weiner, peterx, Martin Cracauer,
	Marty McFadden, Shaohua Li, Andrea Arcangeli, Mike Kravetz,
	Denis Plotnikov, Mike Rapoport, Linus Torvalds, Mel Gorman,
	Kirill A . Shutemov, Dr . David Alan Gilbert

The idea comes from the upstream discussion between Linus and Andrea:

https://lkml.org/lkml/2017/10/30/560

A summary to the issue: there was a special path in handle_userfault()
in the past that we'll return a VM_FAULT_NOPAGE when we detected
non-fatal signals when waiting for userfault handling.  We did that by
reacquiring the mmap_sem before returning.  However that brings a risk
in that the vmas might have changed when we retake the mmap_sem and
even we could be holding an invalid vma structure.

This patch removes the risk path in handle_userfault() then we will be
sure that the callers of handle_mm_fault() will know that the VMAs
might have changed.  Meanwhile with previous patch we don't lose
responsiveness as well since the core mm code now can handle the
nonfatal userspace signals quickly even if we return VM_FAULT_RETRY.

Suggested-by: Andrea Arcangeli <aarcange@redhat.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 fs/userfaultfd.c | 24 ------------------------
 1 file changed, 24 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 4a8ad2dc2b6f..48b7ecf39f25 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -522,30 +522,6 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
 
 	__set_current_state(TASK_RUNNING);
 
-	if (return_to_userland) {
-		if (signal_pending(current) &&
-		    !fatal_signal_pending(current)) {
-			/*
-			 * If we got a SIGSTOP or SIGCONT and this is
-			 * a normal userland page fault, just let
-			 * userland return so the signal will be
-			 * handled and gdb debugging works.  The page
-			 * fault code immediately after we return from
-			 * this function is going to release the
-			 * mmap_sem and it's not depending on it
-			 * (unlike gup would if we were not to return
-			 * VM_FAULT_RETRY).
-			 *
-			 * If a fatal signal is pending we still take
-			 * the streamlined VM_FAULT_RETRY failure path
-			 * and there's no need to retake the mmap_sem
-			 * in such case.
-			 */
-			down_read(&mm->mmap_sem);
-			ret = VM_FAULT_NOPAGE;
-		}
-	}
-
 	/*
 	 * Here we race with the list_del; list_add in
 	 * userfaultfd_ctx_read(), however because we don't ever run
-- 
2.21.0



^ permalink raw reply	[flat|nested] 12+ messages in thread

* [PATCH v3 6/7] mm: Allow VM_FAULT_RETRY for multiple times
  2019-09-11  7:10 [PATCH v3 0/7] mm: Page fault enhancements Peter Xu
                   ` (4 preceding siblings ...)
  2019-09-11  7:10 ` [PATCH v3 5/7] userfaultfd: Don't retake mmap_sem to emulate NOPAGE Peter Xu
@ 2019-09-11  7:10 ` Peter Xu
  2019-09-11  7:10 ` [PATCH v3 7/7] mm/gup: " Peter Xu
  6 siblings, 0 replies; 12+ messages in thread
From: Peter Xu @ 2019-09-11  7:10 UTC (permalink / raw)
  To: linux-mm, linux-kernel
  Cc: David Hildenbrand, Hugh Dickins, Maya Gokhale, Jerome Glisse,
	Pavel Emelyanov, Johannes Weiner, peterx, Martin Cracauer,
	Marty McFadden, Shaohua Li, Andrea Arcangeli, Mike Kravetz,
	Denis Plotnikov, Mike Rapoport, Linus Torvalds, Mel Gorman,
	Kirill A . Shutemov, Dr . David Alan Gilbert

The idea comes from a discussion between Linus and Andrea [1].

Before this patch we only allow a page fault to retry once.  We
achieved this by clearing the FAULT_FLAG_ALLOW_RETRY flag when doing
handle_mm_fault() the second time.  This was majorly used to avoid
unexpected starvation of the system by looping over forever to handle
the page fault on a single page.  However that should hardly happen,
and after all for each code path to return a VM_FAULT_RETRY we'll
first wait for a condition (during which time we should possibly yield
the cpu) to happen before VM_FAULT_RETRY is really returned.

This patch removes the restriction by keeping the
FAULT_FLAG_ALLOW_RETRY flag when we receive VM_FAULT_RETRY.  It means
that the page fault handler now can retry the page fault for multiple
times if necessary without the need to generate another page fault
event.  Meanwhile we still keep the FAULT_FLAG_TRIED flag so page
fault handler can still identify whether a page fault is the first
attempt or not.

Then we'll have these combinations of fault flags (only considering
ALLOW_RETRY flag and TRIED flag):

  - ALLOW_RETRY and !TRIED:  this means the page fault allows to
                             retry, and this is the first try

  - ALLOW_RETRY and TRIED:   this means the page fault allows to
                             retry, and this is not the first try

  - !ALLOW_RETRY and !TRIED: this means the page fault does not allow
                             to retry at all

  - !ALLOW_RETRY and TRIED:  this is forbidden and should never be used

In existing code we have multiple places that has taken special care
of the first condition above by checking against (fault_flags &
FAULT_FLAG_ALLOW_RETRY).  This patch introduces a simple helper to
detect the first retry of a page fault by checking against
both (fault_flags & FAULT_FLAG_ALLOW_RETRY) and !(fault_flag &
FAULT_FLAG_TRIED) because now even the 2nd try will have the
ALLOW_RETRY set, then use that helper in all existing special paths.
One example is in __lock_page_or_retry(), now we'll drop the mmap_sem
only in the first attempt of page fault and we'll keep it in follow up
retries, so old locking behavior will be retained.

This will be a nice enhancement for current code [2] at the same time
a supporting material for the future userfaultfd-writeprotect work,
since in that work there will always be an explicit userfault
writeprotect retry for protected pages, and if that cannot resolve the
page fault (e.g., when userfaultfd-writeprotect is used in conjunction
with swapped pages) then we'll possibly need a 3rd retry of the page
fault.  It might also benefit other potential users who will have
similar requirement like userfault write-protection.

GUP code is not touched yet and will be covered in follow up patch.

Please read the thread below for more information.

[1] https://lkml.org/lkml/2017/11/2/833
[2] https://lkml.org/lkml/2018/12/30/64

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 arch/alpha/mm/fault.c           |  2 +-
 arch/arc/mm/fault.c             |  1 -
 arch/arm/mm/fault.c             |  3 ---
 arch/arm64/mm/fault.c           |  5 -----
 arch/hexagon/mm/vm_fault.c      |  1 -
 arch/ia64/mm/fault.c            |  1 -
 arch/m68k/mm/fault.c            |  3 ---
 arch/microblaze/mm/fault.c      |  1 -
 arch/mips/mm/fault.c            |  1 -
 arch/nds32/mm/fault.c           |  1 -
 arch/nios2/mm/fault.c           |  3 ---
 arch/openrisc/mm/fault.c        |  1 -
 arch/parisc/mm/fault.c          |  4 +---
 arch/powerpc/mm/fault.c         |  6 ------
 arch/riscv/mm/fault.c           |  5 -----
 arch/s390/mm/fault.c            |  5 +----
 arch/sh/mm/fault.c              |  1 -
 arch/sparc/mm/fault_32.c        |  1 -
 arch/sparc/mm/fault_64.c        |  1 -
 arch/um/kernel/trap.c           |  1 -
 arch/unicore32/mm/fault.c       |  4 +---
 arch/x86/mm/fault.c             |  2 --
 arch/xtensa/mm/fault.c          |  1 -
 drivers/gpu/drm/ttm/ttm_bo_vm.c | 12 ++++++++---
 include/linux/mm.h              | 37 +++++++++++++++++++++++++++++++++
 mm/filemap.c                    |  2 +-
 mm/shmem.c                      |  2 +-
 27 files changed, 52 insertions(+), 55 deletions(-)

diff --git a/arch/alpha/mm/fault.c b/arch/alpha/mm/fault.c
index ab1d4212d658..e032d2d03012 100644
--- a/arch/alpha/mm/fault.c
+++ b/arch/alpha/mm/fault.c
@@ -170,7 +170,7 @@ do_page_fault(unsigned long address, unsigned long mmcsr,
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
+			flags |= FAULT_FLAG_TRIED;
 
 			 /* No need to up_read(&mm->mmap_sem) as we would
 			 * have already released it in __lock_page_or_retry
diff --git a/arch/arc/mm/fault.c b/arch/arc/mm/fault.c
index 27adf4e608e4..bbcde83e010a 100644
--- a/arch/arc/mm/fault.c
+++ b/arch/arc/mm/fault.c
@@ -151,7 +151,6 @@ void do_page_fault(unsigned long address, struct pt_regs *regs)
 		 * retry state machine
 		 */
 		if (flags & FAULT_FLAG_ALLOW_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index f00fb4eafe54..5f1fb46a37b0 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -320,9 +320,6 @@ do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 					regs, addr);
 		}
 		if (fault & VM_FAULT_RETRY) {
-			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			* of starvation. */
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 0d3fe0ea6a70..8c26097bcf0d 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -491,12 +491,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
 				return 0;
 		}
 
-		/*
-		 * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk of
-		 * starvation.
-		 */
 		if (mm_flags & FAULT_FLAG_ALLOW_RETRY) {
-			mm_flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			mm_flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}
diff --git a/arch/hexagon/mm/vm_fault.c b/arch/hexagon/mm/vm_fault.c
index 88a2e5635bfb..a299d2142cbb 100644
--- a/arch/hexagon/mm/vm_fault.c
+++ b/arch/hexagon/mm/vm_fault.c
@@ -103,7 +103,6 @@ void do_page_fault(unsigned long address, long cause, struct pt_regs *regs)
 			else
 				current->min_flt++;
 			if (fault & VM_FAULT_RETRY) {
-				flags &= ~FAULT_FLAG_ALLOW_RETRY;
 				flags |= FAULT_FLAG_TRIED;
 				goto retry;
 			}
diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c
index 8d47acf50fda..7679e960c685 100644
--- a/arch/ia64/mm/fault.c
+++ b/arch/ia64/mm/fault.c
@@ -168,7 +168,6 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			 /* No need to up_read(&mm->mmap_sem) as we would
diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
index 103f93ba8139..d4ef4fdf4de4 100644
--- a/arch/m68k/mm/fault.c
+++ b/arch/m68k/mm/fault.c
@@ -163,9 +163,6 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			 * of starvation. */
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/*
diff --git a/arch/microblaze/mm/fault.c b/arch/microblaze/mm/fault.c
index 8b0615eab4b6..9a359568f70a 100644
--- a/arch/microblaze/mm/fault.c
+++ b/arch/microblaze/mm/fault.c
@@ -237,7 +237,6 @@ void do_page_fault(struct pt_regs *regs, unsigned long address,
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/*
diff --git a/arch/mips/mm/fault.c b/arch/mips/mm/fault.c
index 48aac20a1ded..5eeea572ff3f 100644
--- a/arch/mips/mm/fault.c
+++ b/arch/mips/mm/fault.c
@@ -179,7 +179,6 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write,
 			tsk->min_flt++;
 		}
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/*
diff --git a/arch/nds32/mm/fault.c b/arch/nds32/mm/fault.c
index baa44f9d0b4a..954ca83d3289 100644
--- a/arch/nds32/mm/fault.c
+++ b/arch/nds32/mm/fault.c
@@ -243,7 +243,6 @@ void do_page_fault(unsigned long entry, unsigned long addr,
 				      1, regs, addr);
 		}
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/* No need to up_read(&mm->mmap_sem) as we would
diff --git a/arch/nios2/mm/fault.c b/arch/nios2/mm/fault.c
index f9f178484184..07f467577e77 100644
--- a/arch/nios2/mm/fault.c
+++ b/arch/nios2/mm/fault.c
@@ -158,9 +158,6 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long cause,
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			 * of starvation. */
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/*
diff --git a/arch/openrisc/mm/fault.c b/arch/openrisc/mm/fault.c
index 8ba3696dd10c..e7dadbdb21b3 100644
--- a/arch/openrisc/mm/fault.c
+++ b/arch/openrisc/mm/fault.c
@@ -182,7 +182,6 @@ asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long address,
 		else
 			tsk->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			 /* No need to up_read(&mm->mmap_sem) as we would
diff --git a/arch/parisc/mm/fault.c b/arch/parisc/mm/fault.c
index 163dcb080c7b..c837da780a79 100644
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -329,14 +329,12 @@ void do_page_fault(struct pt_regs *regs, unsigned long code,
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
-
 			/*
 			 * No need to up_read(&mm->mmap_sem) as we would
 			 * have already released it in __lock_page_or_retry
 			 * in mm/filemap.c.
 			 */
-
+			flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}
 	}
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index d321a6c5fe62..321f24d0762f 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -588,13 +588,7 @@ static int __do_page_fault(struct pt_regs *regs, unsigned long address,
 	 * case.
 	 */
 	if (unlikely(fault & VM_FAULT_RETRY)) {
-		/* We retry only once */
 		if (flags & FAULT_FLAG_ALLOW_RETRY) {
-			/*
-			 * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			 * of starvation.
-			 */
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 			if (is_user && signal_pending(current))
 				return 0;
diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c
index ea8f301de65b..d1710ef75432 100644
--- a/arch/riscv/mm/fault.c
+++ b/arch/riscv/mm/fault.c
@@ -143,11 +143,6 @@ asmlinkage void do_page_fault(struct pt_regs *regs)
 				      1, regs, addr);
 		}
 		if (fault & VM_FAULT_RETRY) {
-			/*
-			 * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			 * of starvation.
-			 */
-			flags &= ~(FAULT_FLAG_ALLOW_RETRY);
 			flags |= FAULT_FLAG_TRIED;
 
 			/*
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 3ad77501deef..46ef1159d146 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -514,10 +514,7 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 				fault = VM_FAULT_PFAULT;
 				goto out_up;
 			}
-			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			 * of starvation. */
-			flags &= ~(FAULT_FLAG_ALLOW_RETRY |
-				   FAULT_FLAG_RETRY_NOWAIT);
+			flags &= ~FAULT_FLAG_RETRY_NOWAIT;
 			flags |= FAULT_FLAG_TRIED;
 			down_read(&mm->mmap_sem);
 			goto retry;
diff --git a/arch/sh/mm/fault.c b/arch/sh/mm/fault.c
index f620282a37fd..2e9cf3fd395f 100644
--- a/arch/sh/mm/fault.c
+++ b/arch/sh/mm/fault.c
@@ -481,7 +481,6 @@ asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
 				      regs, address);
 		}
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/*
diff --git a/arch/sparc/mm/fault_32.c b/arch/sparc/mm/fault_32.c
index 9af0c3ad50d6..97494086f1e5 100644
--- a/arch/sparc/mm/fault_32.c
+++ b/arch/sparc/mm/fault_32.c
@@ -261,7 +261,6 @@ asmlinkage void do_sparc_fault(struct pt_regs *regs, int text_fault, int write,
 				      1, regs, address);
 		}
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/* No need to up_read(&mm->mmap_sem) as we would
diff --git a/arch/sparc/mm/fault_64.c b/arch/sparc/mm/fault_64.c
index 566f05f9040b..a1730c3a8f30 100644
--- a/arch/sparc/mm/fault_64.c
+++ b/arch/sparc/mm/fault_64.c
@@ -446,7 +446,6 @@ asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
 				      1, regs, address);
 		}
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			/* No need to up_read(&mm->mmap_sem) as we would
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index 3c72111f27e9..063da0930d31 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -98,7 +98,6 @@ int handle_page_fault(unsigned long address, unsigned long ip,
 			else
 				current->min_flt++;
 			if (fault & VM_FAULT_RETRY) {
-				flags &= ~FAULT_FLAG_ALLOW_RETRY;
 				flags |= FAULT_FLAG_TRIED;
 
 				goto retry;
diff --git a/arch/unicore32/mm/fault.c b/arch/unicore32/mm/fault.c
index 04c193439c97..8b3367ec0d80 100644
--- a/arch/unicore32/mm/fault.c
+++ b/arch/unicore32/mm/fault.c
@@ -260,9 +260,7 @@ static int do_pf(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
 		else
 			tsk->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			/* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
-			* of starvation. */
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
+			flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}
 	}
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index f7836472961e..7664f0f89ef6 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1447,9 +1447,7 @@ void do_user_addr_fault(struct pt_regs *regs,
 	 * that we made any progress. Handle this case first.
 	 */
 	if (unlikely(fault & VM_FAULT_RETRY)) {
-		/* Retry at most once */
 		if (flags & FAULT_FLAG_ALLOW_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 			if ((flags & FAULT_FLAG_USER) && signal_pending(tsk))
 				return;
diff --git a/arch/xtensa/mm/fault.c b/arch/xtensa/mm/fault.c
index 094606676c36..1d91a23d27d3 100644
--- a/arch/xtensa/mm/fault.c
+++ b/arch/xtensa/mm/fault.c
@@ -129,7 +129,6 @@ void do_page_fault(struct pt_regs *regs)
 		else
 			current->min_flt++;
 		if (fault & VM_FAULT_RETRY) {
-			flags &= ~FAULT_FLAG_ALLOW_RETRY;
 			flags |= FAULT_FLAG_TRIED;
 
 			 /* No need to up_read(&mm->mmap_sem) as we would
diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 6dacff49c1cc..8f2f9ee6effa 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -61,9 +61,10 @@ static vm_fault_t ttm_bo_vm_fault_idle(struct ttm_buffer_object *bo,
 
 	/*
 	 * If possible, avoid waiting for GPU with mmap_sem
-	 * held.
+	 * held.  We only do this if the fault allows retry and this
+	 * is the first attempt.
 	 */
-	if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
+	if (fault_flag_allow_retry_first(vmf->flags)) {
 		ret = VM_FAULT_RETRY;
 		if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
 			goto out_unlock;
@@ -132,7 +133,12 @@ static vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
 	 * for the buffer to become unreserved.
 	 */
 	if (unlikely(!reservation_object_trylock(bo->resv))) {
-		if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
+		/*
+		 * If the fault allows retry and this is the first
+		 * fault attempt, we try to release the mmap_sem
+		 * before waiting
+		 */
+		if (fault_flag_allow_retry_first(vmf->flags)) {
 			if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
 				ttm_bo_get(bo);
 				up_read(&vmf->vma->vm_mm->mmap_sem);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 53ec7abb8472..0fdbdcb257d6 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -396,6 +396,25 @@ extern pgprot_t protection_map[16];
  * @FAULT_FLAG_REMOTE: The fault is not for current task/mm.
  * @FAULT_FLAG_INSTRUCTION: The fault was during an instruction fetch.
  * @FAULT_FLAG_INTERRUPTIBLE: The fault can be interrupted by non-fatal signals.
+ *
+ * About @FAULT_FLAG_ALLOW_RETRY and @FAULT_FLAG_TRIED: we can specify
+ * whether we would allow page faults to retry by specifying these two
+ * fault flags correctly.  Currently there can be three legal combinations:
+ *
+ * (a) ALLOW_RETRY and !TRIED:  this means the page fault allows retry, and
+ *                              this is the first try
+ *
+ * (b) ALLOW_RETRY and TRIED:   this means the page fault allows retry, and
+ *                              we've already tried at least once
+ *
+ * (c) !ALLOW_RETRY and !TRIED: this means the page fault does not allow retry
+ *
+ * The unlisted combination (!ALLOW_RETRY && TRIED) is illegal and should never
+ * be used.  Note that page faults can be allowed to retry for multiple times,
+ * in which case we'll have an initial fault with flags (a) then later on
+ * continuous faults with flags (b).  We should always try to detect pending
+ * signals before a retry to make sure the continuous page faults can still be
+ * interrupted if necessary.
  */
 #define FAULT_FLAG_WRITE			0x01
 #define FAULT_FLAG_MKWRITE			0x02
@@ -416,6 +435,24 @@ extern pgprot_t protection_map[16];
 			     FAULT_FLAG_KILLABLE | \
 			     FAULT_FLAG_INTERRUPTIBLE)
 
+/**
+ * fault_flag_allow_retry_first - check ALLOW_RETRY the first time
+ *
+ * This is mostly used for places where we want to try to avoid taking
+ * the mmap_sem for too long a time when waiting for another condition
+ * to change, in which case we can try to be polite to release the
+ * mmap_sem in the first round to avoid potential starvation of other
+ * processes that would also want the mmap_sem.
+ *
+ * Return: true if the page fault allows retry and this is the first
+ * attempt of the fault handling; false otherwise.
+ */
+static inline bool fault_flag_allow_retry_first(unsigned int flags)
+{
+	return (flags & FAULT_FLAG_ALLOW_RETRY) &&
+	    (!(flags & FAULT_FLAG_TRIED));
+}
+
 #define FAULT_FLAG_TRACE \
 	{ FAULT_FLAG_WRITE,		"WRITE" }, \
 	{ FAULT_FLAG_MKWRITE,		"MKWRITE" }, \
diff --git a/mm/filemap.c b/mm/filemap.c
index d0cf700bf201..543404617f5a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1399,7 +1399,7 @@ EXPORT_SYMBOL_GPL(__lock_page_killable);
 int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
 			 unsigned int flags)
 {
-	if (flags & FAULT_FLAG_ALLOW_RETRY) {
+	if (fault_flag_allow_retry_first(flags)) {
 		/*
 		 * CAUTION! In this case, mmap_sem is not released
 		 * even though return 0.
diff --git a/mm/shmem.c b/mm/shmem.c
index 626d8c74b973..c32e7101294e 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2011,7 +2011,7 @@ static vm_fault_t shmem_fault(struct vm_fault *vmf)
 			DEFINE_WAIT_FUNC(shmem_fault_wait, synchronous_wake_function);
 
 			ret = VM_FAULT_NOPAGE;
-			if ((vmf->flags & FAULT_FLAG_ALLOW_RETRY) &&
+			if (fault_flag_allow_retry_first(vmf->flags) &&
 			   !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
 				/* It's polite to up mmap_sem if we can */
 				up_read(&vma->vm_mm->mmap_sem);
-- 
2.21.0



^ permalink raw reply	[flat|nested] 12+ messages in thread

* [PATCH v3 7/7] mm/gup: Allow VM_FAULT_RETRY for multiple times
  2019-09-11  7:10 [PATCH v3 0/7] mm: Page fault enhancements Peter Xu
                   ` (5 preceding siblings ...)
  2019-09-11  7:10 ` [PATCH v3 6/7] mm: Allow VM_FAULT_RETRY for multiple times Peter Xu
@ 2019-09-11  7:10 ` " Peter Xu
  2019-09-11  9:45   ` [PATCH v3.1 " Peter Xu
  2019-09-11  9:47   ` [PATCH v3 " Linus Torvalds
  6 siblings, 2 replies; 12+ messages in thread
From: Peter Xu @ 2019-09-11  7:10 UTC (permalink / raw)
  To: linux-mm, linux-kernel
  Cc: David Hildenbrand, Hugh Dickins, Maya Gokhale, Jerome Glisse,
	Pavel Emelyanov, Johannes Weiner, peterx, Martin Cracauer,
	Marty McFadden, Shaohua Li, Andrea Arcangeli, Mike Kravetz,
	Denis Plotnikov, Mike Rapoport, Linus Torvalds, Mel Gorman,
	Kirill A . Shutemov, Dr . David Alan Gilbert

This is the gup counterpart of the change that allows the
VM_FAULT_RETRY to happen for more than once.  One thing to mention is
that we must check the fatal signal here before retry because the GUP
can be interrupted by that, otherwise we can loop forever.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 mm/gup.c     | 25 ++++++++++++++++++++-----
 mm/hugetlb.c |  6 ++++--
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index eddbb95dcb8f..4b9413ee7b23 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -644,7 +644,10 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 	if (*flags & FOLL_NOWAIT)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
 	if (*flags & FOLL_TRIED) {
-		VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
+		/*
+		 * Note: FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_TRIED
+		 * can co-exist
+		 */
 		fault_flags |= FAULT_FLAG_TRIED;
 	}
 
@@ -1059,17 +1062,29 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
 		if (likely(pages))
 			pages += ret;
 		start += ret << PAGE_SHIFT;
+		lock_dropped = true;
 
+retry:
 		/*
 		 * Repeat on the address that fired VM_FAULT_RETRY
-		 * without FAULT_FLAG_ALLOW_RETRY but with
-		 * FAULT_FLAG_TRIED.
+		 * with both FAULT_FLAG_ALLOW_RETRY and
+		 * FAULT_FLAG_TRIED.  Note that GUP can be interrupted
+		 * by fatal signals, so we need to check it before we
+		 * start trying again otherwise it can loop forever.
 		 */
+
+		if (fatal_signal_pending(current))
+			goto out;
+
 		*locked = 1;
-		lock_dropped = true;
 		down_read(&mm->mmap_sem);
 		ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
-				       pages, NULL, NULL);
+				       pages, NULL, locked);
+		if (!*locked) {
+			/* Continue to retry until we succeeded */
+			BUG_ON(ret != 0);
+			goto retry;
+		}
 		if (ret != 1) {
 			BUG_ON(ret > 1);
 			if (!pages_done)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5f816ee42206..6b9d27925e7a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4328,8 +4328,10 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 				fault_flags |= FAULT_FLAG_ALLOW_RETRY |
 					FAULT_FLAG_RETRY_NOWAIT;
 			if (flags & FOLL_TRIED) {
-				VM_WARN_ON_ONCE(fault_flags &
-						FAULT_FLAG_ALLOW_RETRY);
+				/*
+				 * Note: FAULT_FLAG_ALLOW_RETRY and
+				 * FAULT_FLAG_TRIED can co-exist
+				 */
 				fault_flags |= FAULT_FLAG_TRIED;
 			}
 			ret = hugetlb_fault(mm, vma, vaddr, fault_flags);
-- 
2.21.0



^ permalink raw reply	[flat|nested] 12+ messages in thread

* [PATCH v3.1 7/7] mm/gup: Allow VM_FAULT_RETRY for multiple times
  2019-09-11  7:10 ` [PATCH v3 7/7] mm/gup: " Peter Xu
@ 2019-09-11  9:45   ` " Peter Xu
  2019-09-11  9:47   ` [PATCH v3 " Linus Torvalds
  1 sibling, 0 replies; 12+ messages in thread
From: Peter Xu @ 2019-09-11  9:45 UTC (permalink / raw)
  To: linux-mm, linux-kernel
  Cc: Peter Xu, David Hildenbrand, Hugh Dickins, Maya Gokhale,
	Jerome Glisse, Pavel Emelyanov, Johannes Weiner, Martin Cracauer,
	Marty McFadden, Shaohua Li, Andrea Arcangeli, Mike Kravetz,
	Denis Plotnikov, Mike Rapoport, Linus Torvalds, Mel Gorman,
	Kirill A . Shutemov, Dr . David Alan Gilbert

This is the gup counterpart of the change that allows the
VM_FAULT_RETRY to happen for more than once.  One thing to mention is
that we must check the fatal signal here before retry because the GUP
can be interrupted by that, otherwise we can loop forever.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 mm/gup.c     | 25 ++++++++++++++++++++-----
 mm/hugetlb.c |  6 ++++--
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index eddbb95dcb8f..4b9413ee7b23 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -644,7 +644,10 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 	if (*flags & FOLL_NOWAIT)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
 	if (*flags & FOLL_TRIED) {
-		VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
+		/*
+		 * Note: FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_TRIED
+		 * can co-exist
+		 */
 		fault_flags |= FAULT_FLAG_TRIED;
 	}
 
@@ -1059,17 +1062,29 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
 		if (likely(pages))
 			pages += ret;
 		start += ret << PAGE_SHIFT;
+		lock_dropped = true;
 
+retry:
 		/*
 		 * Repeat on the address that fired VM_FAULT_RETRY
-		 * without FAULT_FLAG_ALLOW_RETRY but with
-		 * FAULT_FLAG_TRIED.
+		 * with both FAULT_FLAG_ALLOW_RETRY and
+		 * FAULT_FLAG_TRIED.  Note that GUP can be interrupted
+		 * by fatal signals, so we need to check it before we
+		 * start trying again otherwise it can loop forever.
 		 */
+
+		if (fatal_signal_pending(current))
+			break;
+
 		*locked = 1;
-		lock_dropped = true;
 		down_read(&mm->mmap_sem);
 		ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
-				       pages, NULL, NULL);
+				       pages, NULL, locked);
+		if (!*locked) {
+			/* Continue to retry until we succeeded */
+			BUG_ON(ret != 0);
+			goto retry;
+		}
 		if (ret != 1) {
 			BUG_ON(ret > 1);
 			if (!pages_done)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 31c2a6275023..d0c98cff5b0f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4347,8 +4347,10 @@ long follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 				fault_flags |= FAULT_FLAG_ALLOW_RETRY |
 					FAULT_FLAG_RETRY_NOWAIT;
 			if (flags & FOLL_TRIED) {
-				VM_WARN_ON_ONCE(fault_flags &
-						FAULT_FLAG_ALLOW_RETRY);
+				/*
+				 * Note: FAULT_FLAG_ALLOW_RETRY and
+				 * FAULT_FLAG_TRIED can co-exist
+				 */
 				fault_flags |= FAULT_FLAG_TRIED;
 			}
 			ret = hugetlb_fault(mm, vma, vaddr, fault_flags);
-- 
2.21.0



^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [PATCH v3 7/7] mm/gup: Allow VM_FAULT_RETRY for multiple times
  2019-09-11  7:10 ` [PATCH v3 7/7] mm/gup: " Peter Xu
  2019-09-11  9:45   ` [PATCH v3.1 " Peter Xu
@ 2019-09-11  9:47   ` " Linus Torvalds
  2019-09-12  3:05     ` Peter Xu
  1 sibling, 1 reply; 12+ messages in thread
From: Linus Torvalds @ 2019-09-11  9:47 UTC (permalink / raw)
  To: Peter Xu
  Cc: Linux-MM, Linux List Kernel Mailing, David Hildenbrand,
	Hugh Dickins, Maya Gokhale, Jerome Glisse, Pavel Emelyanov,
	Johannes Weiner, Martin Cracauer, Marty McFadden, Shaohua Li,
	Andrea Arcangeli, Mike Kravetz, Denis Plotnikov, Mike Rapoport,
	Mel Gorman, Kirill A . Shutemov, Dr . David Alan Gilbert

On Wed, Sep 11, 2019 at 8:11 AM Peter Xu <peterx@redhat.com> wrote:
>
> This is the gup counterpart of the change that allows the
> VM_FAULT_RETRY to happen for more than once.  One thing to mention is
> that we must check the fatal signal here before retry because the GUP
> can be interrupted by that, otherwise we can loop forever.

I still get nervous about the signal handling here.

I'm not entirely sure we get it right even before your patch series.

Right now, __get_user_pages() can return -ERESTARTSYS when it's killed:

        /*
         * If we have a pending SIGKILL, don't keep faulting pages and
         * potentially allocating memory.
         */
        if (fatal_signal_pending(current)) {
                ret = -ERESTARTSYS;
                goto out;
        }

and I don't think your series changes that.  And note how this is true
_regardless_ of any FOLL_xyz flags (and we don't pass the
FAULT_FLAG_xyz flags at all, they get generated deeper down if we
actually end up faulting things in).

So this part of the patch:

+               if (fatal_signal_pending(current))
+                       goto out;
+
                *locked = 1;
-               lock_dropped = true;
                down_read(&mm->mmap_sem);
                ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
-                                      pages, NULL, NULL);
+                                      pages, NULL, locked);
+               if (!*locked) {
+                       /* Continue to retry until we succeeded */
+                       BUG_ON(ret != 0);
+                       goto retry;

just makes me go "that can't be right". The fatal_signal_pending() is
pointless and would probably better be something like

        if (down_read_killable(&mm->mmap_sem) < 0)
                goto out;

and then _after_ calling __get_user_pages(), the whole "negative error
handling" should be more obvious.

The BUG_ON(ret != 0) makes me nervous, but it might be fine (I guess
the fatal signal handling has always been done before the lock is
released?).

But exactly *because* __get_user_pages() can already return on fatal
signals, I think it should also set FAULT_FLAG_KILLABLE when faulting
things in. I don't think it does right now, so it doesn't actually
necessarily check fatal signals in a timely manner (not _during_ the
fault, only _before_ it).

See what I'm reacting to?

And maybe I'm wrong. Maybe I misread the code, and your changes. And
at least some of these logic error predate your changes, I just was
hoping that since this whole "react to signals" is very much what your
patch series is working on, you'd look at this.

Ok?

            Linus


^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [PATCH v3 3/7] mm: Introduce FAULT_FLAG_INTERRUPTIBLE
  2019-09-11  7:10 ` [PATCH v3 3/7] mm: Introduce FAULT_FLAG_INTERRUPTIBLE Peter Xu
@ 2019-09-11 10:15   ` David Hildenbrand
  0 siblings, 0 replies; 12+ messages in thread
From: David Hildenbrand @ 2019-09-11 10:15 UTC (permalink / raw)
  To: Peter Xu, linux-mm, linux-kernel
  Cc: Hugh Dickins, Maya Gokhale, Jerome Glisse, Pavel Emelyanov,
	Johannes Weiner, Martin Cracauer, Marty McFadden, Shaohua Li,
	Andrea Arcangeli, Mike Kravetz, Denis Plotnikov, Mike Rapoport,
	Linus Torvalds, Mel Gorman, Kirill A . Shutemov,
	Dr . David Alan Gilbert

On 11.09.19 09:10, Peter Xu wrote:
> handle_userfaultfd() is currently the only one place in the kernel
> page fault procedures that can respond to non-fatal userspace signals.
> It was trying to detect such an allowance by checking against USER &
> KILLABLE flags, which was "un-official".
> 
> In this patch, we introduced a new flag (FAULT_FLAG_INTERRUPTIBLE) to
> show that the fault handler allows the fault procedure to respond even
> to non-fatal signals.  Meanwhile, add this new flag to the default
> fault flags so that all the page fault handlers can benefit from the
> new flag.  With that, replacing the userfault check to this one.
> 
> Since the line is getting even longer, clean up the fault flags a bit
> too to ease TTY users.
> 
> Although we've got a new flag and applied it, we shouldn't have any
> functional change with this patch so far.
> 
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  fs/userfaultfd.c   |  4 +---
>  include/linux/mm.h | 39 ++++++++++++++++++++++++++++-----------
>  2 files changed, 29 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index ccbdbd62f0d8..4a8ad2dc2b6f 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -462,9 +462,7 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
>  	uwq.ctx = ctx;
>  	uwq.waken = false;
>  
> -	return_to_userland =
> -		(vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
> -		(FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
> +	return_to_userland = vmf->flags & FAULT_FLAG_INTERRUPTIBLE;
>  	blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
>  			 TASK_KILLABLE;
>  
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 57fb5c535f8e..53ec7abb8472 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -383,22 +383,38 @@ extern unsigned int kobjsize(const void *objp);
>   */
>  extern pgprot_t protection_map[16];
>  
> -#define FAULT_FLAG_WRITE	0x01	/* Fault was a write access */
> -#define FAULT_FLAG_MKWRITE	0x02	/* Fault was mkwrite of existing pte */
> -#define FAULT_FLAG_ALLOW_RETRY	0x04	/* Retry fault if blocking */
> -#define FAULT_FLAG_RETRY_NOWAIT	0x08	/* Don't drop mmap_sem and wait when retrying */
> -#define FAULT_FLAG_KILLABLE	0x10	/* The fault task is in SIGKILL killable region */
> -#define FAULT_FLAG_TRIED	0x20	/* Second try */
> -#define FAULT_FLAG_USER		0x40	/* The fault originated in userspace */
> -#define FAULT_FLAG_REMOTE	0x80	/* faulting for non current tsk/mm */
> -#define FAULT_FLAG_INSTRUCTION  0x100	/* The fault was during an instruction fetch */
> +/**
> + * Fault flag definitions.
> + *
> + * @FAULT_FLAG_WRITE: Fault was a write fault.
> + * @FAULT_FLAG_MKWRITE: Fault was mkwrite of existing PTE.
> + * @FAULT_FLAG_ALLOW_RETRY: Allow to retry the fault if blocked.
> + * @FAULT_FLAG_RETRY_NOWAIT: Don't drop mmap_sem and wait when retrying.
> + * @FAULT_FLAG_KILLABLE: The fault task is in SIGKILL killable region.
> + * @FAULT_FLAG_TRIED: The fault has been tried once.
> + * @FAULT_FLAG_USER: The fault originated in userspace.
> + * @FAULT_FLAG_REMOTE: The fault is not for current task/mm.
> + * @FAULT_FLAG_INSTRUCTION: The fault was during an instruction fetch.
> + * @FAULT_FLAG_INTERRUPTIBLE: The fault can be interrupted by non-fatal signals.
> + */
> +#define FAULT_FLAG_WRITE			0x01
> +#define FAULT_FLAG_MKWRITE			0x02
> +#define FAULT_FLAG_ALLOW_RETRY			0x04
> +#define FAULT_FLAG_RETRY_NOWAIT			0x08
> +#define FAULT_FLAG_KILLABLE			0x10
> +#define FAULT_FLAG_TRIED			0x20
> +#define FAULT_FLAG_USER				0x40
> +#define FAULT_FLAG_REMOTE			0x80
> +#define FAULT_FLAG_INSTRUCTION  		0x100
> +#define FAULT_FLAG_INTERRUPTIBLE		0x200
>  
>  /*
>   * The default fault flags that should be used by most of the
>   * arch-specific page fault handlers.
>   */
>  #define FAULT_FLAG_DEFAULT  (FAULT_FLAG_ALLOW_RETRY | \
> -			     FAULT_FLAG_KILLABLE)
> +			     FAULT_FLAG_KILLABLE | \
> +			     FAULT_FLAG_INTERRUPTIBLE)
>  
>  #define FAULT_FLAG_TRACE \
>  	{ FAULT_FLAG_WRITE,		"WRITE" }, \
> @@ -409,7 +425,8 @@ extern pgprot_t protection_map[16];
>  	{ FAULT_FLAG_TRIED,		"TRIED" }, \
>  	{ FAULT_FLAG_USER,		"USER" }, \
>  	{ FAULT_FLAG_REMOTE,		"REMOTE" }, \
> -	{ FAULT_FLAG_INSTRUCTION,	"INSTRUCTION" }
> +	{ FAULT_FLAG_INSTRUCTION,	"INSTRUCTION" }, \
> +	{ FAULT_FLAG_INTERRUPTIBLE,	"INTERRUPTIBLE" }
>  
>  /*
>   * vm_fault is filled by the the pagefault handler and passed to the vma's
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 

Thanks,

David / dhildenb


^ permalink raw reply	[flat|nested] 12+ messages in thread

* Re: [PATCH v3 7/7] mm/gup: Allow VM_FAULT_RETRY for multiple times
  2019-09-11  9:47   ` [PATCH v3 " Linus Torvalds
@ 2019-09-12  3:05     ` Peter Xu
  0 siblings, 0 replies; 12+ messages in thread
From: Peter Xu @ 2019-09-12  3:05 UTC (permalink / raw)
  To: Linus Torvalds
  Cc: Linux-MM, Linux List Kernel Mailing, David Hildenbrand,
	Hugh Dickins, Maya Gokhale, Jerome Glisse, Pavel Emelyanov,
	Johannes Weiner, Martin Cracauer, Marty McFadden, Shaohua Li,
	Andrea Arcangeli, Mike Kravetz, Denis Plotnikov, Mike Rapoport,
	Mel Gorman, Kirill A . Shutemov, Dr . David Alan Gilbert

On Wed, Sep 11, 2019 at 10:47:59AM +0100, Linus Torvalds wrote:
> On Wed, Sep 11, 2019 at 8:11 AM Peter Xu <peterx@redhat.com> wrote:
> >
> > This is the gup counterpart of the change that allows the
> > VM_FAULT_RETRY to happen for more than once.  One thing to mention is
> > that we must check the fatal signal here before retry because the GUP
> > can be interrupted by that, otherwise we can loop forever.
> 
> I still get nervous about the signal handling here.
> 
> I'm not entirely sure we get it right even before your patch series.
> 
> Right now, __get_user_pages() can return -ERESTARTSYS when it's killed:
> 
>         /*
>          * If we have a pending SIGKILL, don't keep faulting pages and
>          * potentially allocating memory.
>          */
>         if (fatal_signal_pending(current)) {
>                 ret = -ERESTARTSYS;
>                 goto out;
>         }
> 
> and I don't think your series changes that.  And note how this is true
> _regardless_ of any FOLL_xyz flags (and we don't pass the
> FAULT_FLAG_xyz flags at all, they get generated deeper down if we
> actually end up faulting things in).
> 
> So this part of the patch:
> 
> +               if (fatal_signal_pending(current))
> +                       goto out;
> +
>                 *locked = 1;
> -               lock_dropped = true;
>                 down_read(&mm->mmap_sem);
>                 ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
> -                                      pages, NULL, NULL);
> +                                      pages, NULL, locked);
> +               if (!*locked) {
> +                       /* Continue to retry until we succeeded */
> +                       BUG_ON(ret != 0);
> +                       goto retry;
> 
> just makes me go "that can't be right". The fatal_signal_pending() is
> pointless and would probably better be something like
> 
>         if (down_read_killable(&mm->mmap_sem) < 0)
>                 goto out;

Thanks for noticing all these!  I'd admit when I was working on the
series I didn't think & test very carefully with fatal signals but
mostly I'm making sure the normal signals should work especially for
processes like userfaultfd tracees so they won't hang death (I'm
always testing with GDB, and if without proper signal handle they do
hang death..).

I agree that we should probably replace the down_read() with the
killable version as you suggested.  Though we might still want the
explicit check of fatal_signal_pending() to make sure we react even
faster because IMHO down_read_killable() does not really check signals
all the time but it just put us into killable state if we need to wait
for the mmap_sem.  In other words, if we are always lucky that we get
the lock without even waiting anything then down_read_killable() will
still ignore the fatal signals forever.

> 
> and then _after_ calling __get_user_pages(), the whole "negative error
> handling" should be more obvious.
> 
> The BUG_ON(ret != 0) makes me nervous, but it might be fine (I guess
> the fatal signal handling has always been done before the lock is
> released?).

Yes it indeed looks nervous, though it's probably should be true in
all cases.  Actually we already have checks like this, for example, in
current __get_user_pages_locked():

        /* VM_FAULT_RETRY cannot return errors */
        if (!*locked) {
                BUG_ON(ret < 0);
                BUG_ON(ret >= nr_pages);
        }

And in the new retry path since we always pass in npages==1 so it must
be zero when VM_FAULT_RETRY.

While... When I'm looking into this more carefully I seem to have
found another bug that we might want to fix with hugetlbfs path:

diff --git a/mm/gup.c b/mm/gup.c
index 7230f60a68d6..29ee3de65fad 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -836,6 +836,16 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                                i = follow_hugetlb_page(mm, vma, pages, vmas,
                                                &start, &nr_pages, i,
                                                gup_flags, locked);
+                               if (locked && *locked == 0) {
+                                       /*
+                                        * We've got a VM_FAULT_RETRY
+                                        * and we've lost mmap_sem.
+                                        * We must stop here.
+                                        */
+                                       BUG_ON(gup_flags & FOLL_NOWAIT);
+                                       BUG_ON(ret != 0);
+                                       goto out;
+                               }
                                continue;
                        }
                }

The problem is that if *locked==0 then we've lost the mmap_sem
already!  Then we probably can't go any further before taking it back
again.  With that, we should be able to keep the previous assumption
valid.

> 
> But exactly *because* __get_user_pages() can already return on fatal
> signals, I think it should also set FAULT_FLAG_KILLABLE when faulting
> things in. I don't think it does right now, so it doesn't actually
> necessarily check fatal signals in a timely manner (not _during_ the
> fault, only _before_ it).

Probably correct again at least to me...

So for current gup we never use FAULT_FLAG_KILLABLE.  However I can't
figure out a reason on why we should continue with anything if the
thread context is going to be destroyed after all.  And since we're at
it, I also noticed that userfaultfd will react upon fatal signals even
without FAULT_FLAG_KILLABLE.  So, here's the things that I think could
be good to have probably in my next post:

- Allow the gup code to always use FAULT_FLAG_KILLABLE as long as
  FAULT_FLAG_ALLOW_RETRY && !FAULT_FLAG_NOWAIT (that should be when
  "locked" parameter is passed into gup), and,

- With previous change, we touch up handle_userfault() to also respect
  the fault flag, so instead of:
  
	blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
			 TASK_KILLABLE;

  We now let the blocking_state to be either (1) INTERRUPTIBLE, if
  with the new FAULT_FLAG_INTERRUPTIBLE, or (2) KILLABLE, if with
  FAULT_FLAG_KILLABLE, or (3) UNINTERRUPTIBLE.  Though if we start to
  use FAULT_FLAG_KILLABLE in gup codes then in most cases (both gup
  and the default page fault flags that most archs use) the
  userfaultfd code should also behave as before.

Does above make any sense?

There could also be considerations behind on the current model of
handling fatal signals that I totally overlooked.  I would appreciate
if anyone can point that out if so.

> 
> See what I'm reacting to?
> 
> And maybe I'm wrong. Maybe I misread the code, and your changes. And
> at least some of these logic error predate your changes, I just was
> hoping that since this whole "react to signals" is very much what your
> patch series is working on, you'd look at this.

Yes, I'd be happy to (as long as they can be reviewed properly so I
can get a chance to fix all my potential mistakes :).

Thanks,

-- 
Peter Xu


^ permalink raw reply	[flat|nested] 12+ messages in thread

end of thread, back to index

Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-09-11  7:10 [PATCH v3 0/7] mm: Page fault enhancements Peter Xu
2019-09-11  7:10 ` [PATCH v3 1/7] mm/gup: Rename "nonblocking" to "locked" where proper Peter Xu
2019-09-11  7:10 ` [PATCH v3 2/7] mm: Introduce FAULT_FLAG_DEFAULT Peter Xu
2019-09-11  7:10 ` [PATCH v3 3/7] mm: Introduce FAULT_FLAG_INTERRUPTIBLE Peter Xu
2019-09-11 10:15   ` David Hildenbrand
2019-09-11  7:10 ` [PATCH v3 4/7] mm: Return faster for non-fatal signals in user mode faults Peter Xu
2019-09-11  7:10 ` [PATCH v3 5/7] userfaultfd: Don't retake mmap_sem to emulate NOPAGE Peter Xu
2019-09-11  7:10 ` [PATCH v3 6/7] mm: Allow VM_FAULT_RETRY for multiple times Peter Xu
2019-09-11  7:10 ` [PATCH v3 7/7] mm/gup: " Peter Xu
2019-09-11  9:45   ` [PATCH v3.1 " Peter Xu
2019-09-11  9:47   ` [PATCH v3 " Linus Torvalds
2019-09-12  3:05     ` Peter Xu

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