From: tip-bot for David Hildenbrand <tipbot@zytor.com>
To: linux-tip-commits@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
tglx@linutronix.de, torvalds@linux-foundation.org,
peterz@infradead.org, hpa@zytor.com, dahi@linux.vnet.ibm.com
Subject: [tip:sched/core] sched/preempt, mm/fault: Trigger might_sleep() in might_fault() with disabled pagefaults
Date: Tue, 19 May 2015 00:18:35 -0700 [thread overview]
Message-ID: <tip-9ec23531fd48031d1b6ca5366f5f967d17a8bc28@git.kernel.org> (raw)
In-Reply-To: <1431359540-32227-3-git-send-email-dahi@linux.vnet.ibm.com>
Commit-ID: 9ec23531fd48031d1b6ca5366f5f967d17a8bc28
Gitweb: http://git.kernel.org/tip/9ec23531fd48031d1b6ca5366f5f967d17a8bc28
Author: David Hildenbrand <dahi@linux.vnet.ibm.com>
AuthorDate: Mon, 11 May 2015 17:52:07 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 19 May 2015 08:39:14 +0200
sched/preempt, mm/fault: Trigger might_sleep() in might_fault() with disabled pagefaults
Commit 662bbcb2747c ("mm, sched: Allow uaccess in atomic with
pagefault_disable()") removed might_sleep() checks for all user access
code (that uses might_fault()).
The reason was to disable wrong "sleep in atomic" warnings in the
following scenario:
pagefault_disable()
rc = copy_to_user(...)
pagefault_enable()
Which is valid, as pagefault_disable() increments the preempt counter
and therefore disables the pagefault handler. copy_to_user() will not
sleep and return an error code if a page is not available.
However, as all might_sleep() checks are removed,
CONFIG_DEBUG_ATOMIC_SLEEP would no longer detect the following scenario:
spin_lock(&lock);
rc = copy_to_user(...)
spin_unlock(&lock)
If the kernel is compiled with preemption turned on, preempt_disable()
will make in_atomic() detect disabled preemption. The fault handler would
correctly never sleep on user access.
However, with preemption turned off, preempt_disable() is usually a NOP
(with !CONFIG_PREEMPT_COUNT), therefore in_atomic() will not be able to
detect disabled preemption nor disabled pagefaults. The fault handler
could sleep.
We really want to enable CONFIG_DEBUG_ATOMIC_SLEEP checks for user access
functions again, otherwise we can end up with horrible deadlocks.
Root of all evil is that pagefault_disable() acts almost as
preempt_disable(), depending on preemption being turned on/off.
As we now have pagefault_disabled(), we can use it to distinguish
whether user acces functions might sleep.
Convert might_fault() into a makro that calls __might_fault(), to
allow proper file + line messages in case of a might_sleep() warning.
Reviewed-and-tested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: David.Laight@ACULAB.COM
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: airlied@linux.ie
Cc: akpm@linux-foundation.org
Cc: benh@kernel.crashing.org
Cc: bigeasy@linutronix.de
Cc: borntraeger@de.ibm.com
Cc: daniel.vetter@intel.com
Cc: heiko.carstens@de.ibm.com
Cc: herbert@gondor.apana.org.au
Cc: hocko@suse.cz
Cc: hughd@google.com
Cc: mst@redhat.com
Cc: paulus@samba.org
Cc: ralf@linux-mips.org
Cc: schwidefsky@de.ibm.com
Cc: yang.shi@windriver.com
Link: http://lkml.kernel.org/r/1431359540-32227-3-git-send-email-dahi@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
include/linux/kernel.h | 3 ++-
mm/memory.c | 18 ++++++------------
2 files changed, 8 insertions(+), 13 deletions(-)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 3a5b48e..060dd7b 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -244,7 +244,8 @@ static inline u32 reciprocal_scale(u32 val, u32 ep_ro)
#if defined(CONFIG_MMU) && \
(defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP))
-void might_fault(void);
+#define might_fault() __might_fault(__FILE__, __LINE__)
+void __might_fault(const char *file, int line);
#else
static inline void might_fault(void) { }
#endif
diff --git a/mm/memory.c b/mm/memory.c
index 22e037e..17734c3 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3737,7 +3737,7 @@ void print_vma_addr(char *prefix, unsigned long ip)
}
#if defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP)
-void might_fault(void)
+void __might_fault(const char *file, int line)
{
/*
* Some code (nfs/sunrpc) uses socket ops on kernel memory while
@@ -3747,21 +3747,15 @@ void might_fault(void)
*/
if (segment_eq(get_fs(), KERNEL_DS))
return;
-
- /*
- * it would be nicer only to annotate paths which are not under
- * pagefault_disable, however that requires a larger audit and
- * providing helpers like get_user_atomic.
- */
- if (in_atomic())
+ if (pagefault_disabled())
return;
-
- __might_sleep(__FILE__, __LINE__, 0);
-
+ __might_sleep(file, line, 0);
+#if defined(CONFIG_DEBUG_ATOMIC_SLEEP)
if (current->mm)
might_lock_read(¤t->mm->mmap_sem);
+#endif
}
-EXPORT_SYMBOL(might_fault);
+EXPORT_SYMBOL(__might_fault);
#endif
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
next prev parent reply other threads:[~2015-05-19 7:19 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-11 15:52 [PATCH v1 00/15] decouple pagefault_disable() from preempt_disable() David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 01/15] uaccess: count pagefault_disable() levels in pagefault_disabled David Hildenbrand
2015-05-19 7:18 ` [tip:sched/core] sched/preempt, mm/fault: Count pagefault_disable () " tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 02/15] mm, uaccess: trigger might_sleep() in might_fault() with disabled pagefaults David Hildenbrand
2015-05-19 7:18 ` tip-bot for David Hildenbrand [this message]
2015-05-11 15:52 ` [PATCH v1 03/15] uaccess: clarify that uaccess may only sleep if pagefaults are enabled David Hildenbrand
2015-05-19 7:18 ` [tip:sched/core] mm/uaccess, mm/fault: Clarify " tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 04/15] mm: explicitly disable/enable preemption in kmap_atomic_* David Hildenbrand
2015-05-19 7:19 ` [tip:sched/core] sched/preempt, mm/kmap: Explicitly disable/ enable " tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 05/15] mips: kmap_coherent relies on disabled preemption David Hildenbrand
2015-05-19 7:19 ` [tip:sched/core] sched/preempt, mm/kmap, MIPS: Disable preemption in kmap_coherent() explicitly tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 06/15] mm: use pagefault_disable() to check for disabled pagefaults in the handler David Hildenbrand
2015-05-19 7:19 ` [tip:sched/core] mm/fault, arch: Use " tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 07/15] drm/i915: use pagefault_disabled() to check for disabled pagefaults David Hildenbrand
2015-05-19 7:20 ` [tip:sched/core] mm/fault, drm/i915: Use " tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 08/15] futex: UP futex_atomic_op_inuser() relies on disabled preemption David Hildenbrand
2015-05-19 7:20 ` [tip:sched/core] sched/preempt, futex: Disable preemption in UP futex_atomic_op_inuser() explicitly tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 09/15] futex: UP futex_atomic_cmpxchg_inatomic() relies on disabled preemption David Hildenbrand
2015-05-19 7:20 ` [tip:sched/core] sched/preempt, futex: Disable preemption in UP futex_atomic_cmpxchg_inatomic() explicitly tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 10/15] arm/futex: UP futex_atomic_cmpxchg_inatomic() relies on disabled preemption David Hildenbrand
2015-05-19 7:21 ` [tip:sched/core] sched/preempt, arm/futex: Disable preemption in UP futex_atomic_cmpxchg_inatomic() explicitly tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 11/15] arm/futex: UP futex_atomic_op_inuser() relies on disabled preemption David Hildenbrand
2015-05-12 19:00 ` Sebastian Andrzej Siewior
2015-05-13 7:38 ` David Hildenbrand
2015-05-13 8:19 ` Sebastian Andrzej Siewior
2015-05-13 8:55 ` David Hildenbrand
2015-05-19 7:21 ` [tip:sched/core] sched/preempt, arm/futex: Disable preemption in UP futex_atomic_op_inuser() explicitly tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 12/15] futex: clarify that preemption doesn't have to be disabled David Hildenbrand
2015-05-19 7:21 ` [tip:sched/core] sched/preempt, futex: Update comments to " tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 13/15] powerpc: enable_kernel_altivec() requires disabled preemption David Hildenbrand
2015-05-19 7:22 ` [tip:sched/core] sched/preempt, powerpc: Disable preemption in enable_kernel_altivec() explicitly tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 14/15] mips: properly lock access to the fpu David Hildenbrand
2015-05-19 7:22 ` [tip:sched/core] sched/preempt, MIPS: Properly lock access to the FPU tip-bot for David Hildenbrand
2015-05-11 15:52 ` [PATCH v1 15/15] uaccess: decouple preemption from the pagefault logic David Hildenbrand
2015-05-19 7:22 ` [tip:sched/core] sched/preempt, mm/fault: Decouple preemption from the page fault logic tip-bot for David Hildenbrand
2015-05-15 14:23 ` [PATCH v1 00/15] decouple pagefault_disable() from preempt_disable() Thomas Gleixner
2015-05-18 12:46 ` David Hildenbrand
2015-05-18 13:04 ` Peter Zijlstra
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