* [PATCH] xfs: reintroduce PF_FSTRANS for transaction reservation recursion protection
@ 2020-06-20 7:12 Yafang Shao
2020-06-21 23:04 ` Dave Chinner
0 siblings, 1 reply; 3+ messages in thread
From: Yafang Shao @ 2020-06-20 7:12 UTC (permalink / raw)
To: david, mhocko, darrick.wong, hch, akpm, bfoster, vbabka
Cc: linux-xfs, linux-fsdevel, linux-mm, Yafang Shao
PF_FSTRANS which is used to avoid transaction reservation recursion, is
dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to
PF_MEMALLOC_NOFS") and commit 7dea19f9ee63 ("mm: introduce
memalloc_nofs_{save,restore} API") and replaced by PF_MEMALLOC_NOFS which
means to avoid filesystem reclaim recursion. That change is subtle.
Let's take the exmple of the check of WARN_ON_ONCE(current->flags &
PF_MEMALLOC_NOFS)) to explain why this abstraction from PF_FSTRANS to
PF_MEMALLOC_NOFS is not proper.
Bellow comment is quoted from Dave,
> It wasn't for memory allocation recursion protection in XFS - it was for
> transaction reservation recursion protection by something trying to flush
> data pages while holding a transaction reservation. Doing
> this could deadlock the journal because the existing reservation
> could prevent the nested reservation for being able to reserve space
> in the journal and that is a self-deadlock vector.
> IOWs, this check is not protecting against memory reclaim recursion
> bugs at all (that's the previous check [1]). This check is
> protecting against the filesystem calling writepages directly from a
> context where it can self-deadlock.
> So what we are seeing here is that the PF_FSTRANS ->
> PF_MEMALLOC_NOFS abstraction lost all the actual useful information
> about what type of error this check was protecting against.
Besides reintroducing PF_FSTRANS, there're some other improvements in this
patch,
- Remove useless MACRO current_clear_flags_nested(), current_pid() and
current_test_flags().
- Remove useless memalloc_nofs_{save, restore} in __kmem_vmalloc()
[1]. Bellow check is to avoid memory reclaim recursion.
if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
PF_MEMALLOC))
goto redirty;
Cc: Dave Chinner <david@fromorbit.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
fs/iomap/buffered-io.c | 4 ++--
fs/xfs/kmem.c | 7 -------
fs/xfs/kmem.h | 2 +-
fs/xfs/libxfs/xfs_btree.c | 2 +-
fs/xfs/xfs_aops.c | 4 ++--
fs/xfs/xfs_linux.h | 4 ----
fs/xfs/xfs_trans.c | 12 ++++++------
include/linux/sched.h | 1 +
8 files changed, 13 insertions(+), 23 deletions(-)
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index bcfc288..0f1945c 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1500,9 +1500,9 @@ static void iomap_writepage_end_bio(struct bio *bio)
/*
* Given that we do not allow direct reclaim to call us, we should
- * never be called in a recursive filesystem reclaim context.
+ * never be called while in a filesystem transaction.
*/
- if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
+ if (WARN_ON_ONCE(current->flags & PF_FSTRANS))
goto redirty;
/*
diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
index f136647..9875a23 100644
--- a/fs/xfs/kmem.c
+++ b/fs/xfs/kmem.c
@@ -41,18 +41,11 @@
static void *
__kmem_vmalloc(size_t size, xfs_km_flags_t flags)
{
- unsigned nofs_flag = 0;
void *ptr;
gfp_t lflags = kmem_flags_convert(flags);
- if (flags & KM_NOFS)
- nofs_flag = memalloc_nofs_save();
-
ptr = __vmalloc(size, lflags);
- if (flags & KM_NOFS)
- memalloc_nofs_restore(nofs_flag);
-
return ptr;
}
diff --git a/fs/xfs/kmem.h b/fs/xfs/kmem.h
index 34cbcfd..ccc63de 100644
--- a/fs/xfs/kmem.h
+++ b/fs/xfs/kmem.h
@@ -34,7 +34,7 @@
BUG_ON(flags & ~(KM_NOFS | KM_MAYFAIL | KM_ZERO | KM_NOLOCKDEP));
lflags = GFP_KERNEL | __GFP_NOWARN;
- if (flags & KM_NOFS)
+ if (current->flags & PF_FSTRANS || flags & KM_NOFS)
lflags &= ~__GFP_FS;
/*
diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
index 2d25bab..65d0afe 100644
--- a/fs/xfs/libxfs/xfs_btree.c
+++ b/fs/xfs/libxfs/xfs_btree.c
@@ -2814,7 +2814,7 @@ struct xfs_btree_split_args {
struct xfs_btree_split_args *args = container_of(work,
struct xfs_btree_split_args, work);
unsigned long pflags;
- unsigned long new_pflags = PF_MEMALLOC_NOFS;
+ unsigned long new_pflags = PF_FSTRANS;
/*
* we are in a transaction context here, but may also be doing work
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index b356118..02733eb 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -62,7 +62,7 @@ static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend)
* We hand off the transaction to the completion thread now, so
* clear the flag here.
*/
- current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
return 0;
}
@@ -125,7 +125,7 @@ static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend)
* thus we need to mark ourselves as being in a transaction manually.
* Similarly for freeze protection.
*/
- current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ current_set_flags_nested(&tp->t_pflags, PF_FSTRANS);
__sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS);
/* we abort the update if there was an IO error */
diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
index 9f70d2f..ab737fe 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h
@@ -102,12 +102,8 @@
#define xfs_cowb_secs xfs_params.cowb_timer.val
#define current_cpu() (raw_smp_processor_id())
-#define current_pid() (current->pid)
-#define current_test_flags(f) (current->flags & (f))
#define current_set_flags_nested(sp, f) \
(*(sp) = current->flags, current->flags |= (f))
-#define current_clear_flags_nested(sp, f) \
- (*(sp) = current->flags, current->flags &= ~(f))
#define current_restore_flags_nested(sp, f) \
(current->flags = ((current->flags & ~(f)) | (*(sp) & (f))))
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 3c94e5f..1c1b982 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -153,7 +153,7 @@
bool rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0;
/* Mark this thread as being in a transaction */
- current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ current_set_flags_nested(&tp->t_pflags, PF_FSTRANS);
/*
* Attempt to reserve the needed disk blocks by decrementing
@@ -163,7 +163,7 @@
if (blocks > 0) {
error = xfs_mod_fdblocks(mp, -((int64_t)blocks), rsvd);
if (error != 0) {
- current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
return -ENOSPC;
}
tp->t_blk_res += blocks;
@@ -240,7 +240,7 @@
tp->t_blk_res = 0;
}
- current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
return error;
}
@@ -861,7 +861,7 @@
xfs_log_commit_cil(mp, tp, &commit_lsn, regrant);
- current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
xfs_trans_free(tp);
/*
@@ -893,7 +893,7 @@
xfs_log_ticket_ungrant(mp->m_log, tp->t_ticket);
tp->t_ticket = NULL;
}
- current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
xfs_trans_free_items(tp, !!error);
xfs_trans_free(tp);
@@ -954,7 +954,7 @@
}
/* mark this thread as no longer being in a transaction */
- current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
xfs_trans_free_items(tp, dirty);
xfs_trans_free(tp);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index b62e6aa..02045e8 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1511,6 +1511,7 @@ static inline int is_global_init(struct task_struct *tsk)
#define PF_KTHREAD 0x00200000 /* I am a kernel thread */
#define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */
#define PF_SWAPWRITE 0x00800000 /* Allowed to write to swap */
+#define PF_FSTRANS 0x01000000 /* Inside a filesystem transaction */
#define PF_UMH 0x02000000 /* I'm an Usermodehelper process */
#define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_mask */
#define PF_MCE_EARLY 0x08000000 /* Early kill for mce process policy */
--
1.8.3.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] xfs: reintroduce PF_FSTRANS for transaction reservation recursion protection
2020-06-20 7:12 [PATCH] xfs: reintroduce PF_FSTRANS for transaction reservation recursion protection Yafang Shao
@ 2020-06-21 23:04 ` Dave Chinner
2020-06-22 12:18 ` Yafang Shao
0 siblings, 1 reply; 3+ messages in thread
From: Dave Chinner @ 2020-06-21 23:04 UTC (permalink / raw)
To: Yafang Shao
Cc: mhocko, darrick.wong, hch, akpm, bfoster, vbabka, linux-xfs,
linux-fsdevel, linux-mm
On Sat, Jun 20, 2020 at 03:12:54AM -0400, Yafang Shao wrote:
> PF_FSTRANS which is used to avoid transaction reservation recursion, is
> dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to
> PF_MEMALLOC_NOFS") and commit 7dea19f9ee63 ("mm: introduce
> memalloc_nofs_{save,restore} API") and replaced by PF_MEMALLOC_NOFS which
> means to avoid filesystem reclaim recursion. That change is subtle.
> Let's take the exmple of the check of WARN_ON_ONCE(current->flags &
> PF_MEMALLOC_NOFS)) to explain why this abstraction from PF_FSTRANS to
> PF_MEMALLOC_NOFS is not proper.
>
> Bellow comment is quoted from Dave,
> > It wasn't for memory allocation recursion protection in XFS - it was for
> > transaction reservation recursion protection by something trying to flush
> > data pages while holding a transaction reservation. Doing
> > this could deadlock the journal because the existing reservation
> > could prevent the nested reservation for being able to reserve space
> > in the journal and that is a self-deadlock vector.
> > IOWs, this check is not protecting against memory reclaim recursion
> > bugs at all (that's the previous check [1]). This check is
> > protecting against the filesystem calling writepages directly from a
> > context where it can self-deadlock.
> > So what we are seeing here is that the PF_FSTRANS ->
> > PF_MEMALLOC_NOFS abstraction lost all the actual useful information
> > about what type of error this check was protecting against.
>
> Besides reintroducing PF_FSTRANS, there're some other improvements in this
> patch,
> - Remove useless MACRO current_clear_flags_nested(), current_pid() and
> current_test_flags().
> - Remove useless memalloc_nofs_{save, restore} in __kmem_vmalloc()
>
> [1]. Bellow check is to avoid memory reclaim recursion.
> if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
> PF_MEMALLOC))
> goto redirty;
>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> ---
> fs/iomap/buffered-io.c | 4 ++--
> fs/xfs/kmem.c | 7 -------
> fs/xfs/kmem.h | 2 +-
> fs/xfs/libxfs/xfs_btree.c | 2 +-
> fs/xfs/xfs_aops.c | 4 ++--
> fs/xfs/xfs_linux.h | 4 ----
> fs/xfs/xfs_trans.c | 12 ++++++------
> include/linux/sched.h | 1 +
> 8 files changed, 13 insertions(+), 23 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index bcfc288..0f1945c 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1500,9 +1500,9 @@ static void iomap_writepage_end_bio(struct bio *bio)
>
> /*
> * Given that we do not allow direct reclaim to call us, we should
> - * never be called in a recursive filesystem reclaim context.
> + * never be called while in a filesystem transaction.
> */
> - if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
> + if (WARN_ON_ONCE(current->flags & PF_FSTRANS))
> goto redirty;
This is OK, but the rest of the patch is not.
I did not say "replace all XFS use of GFP_NOFS/KM_NOFS with
PF_TRANS", which is what this patch does. The use of
PF_MEMALLOC_NOFS within transactions is correct and valid and needs
to remain. Replacing this with PF_FSTRANS effectively reverts all
the simplifications and obviously self-documneting code that
PF_MEMALLOC_NOFS provides us with.
IOWs, PF_MEMALLOC_NOFS is used to indicate that this is a "no
reclaim recursion" path and so it's use remains completely unchanged
in XFS. PF_FSTRANS is to indicate this is a "no
transaction recursion" path, which is a different thing and needs
it's own specific annotation.
> diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> index f136647..9875a23 100644
> --- a/fs/xfs/kmem.c
> +++ b/fs/xfs/kmem.c
> @@ -41,18 +41,11 @@
> static void *
> __kmem_vmalloc(size_t size, xfs_km_flags_t flags)
> {
> - unsigned nofs_flag = 0;
> void *ptr;
> gfp_t lflags = kmem_flags_convert(flags);
>
> - if (flags & KM_NOFS)
> - nofs_flag = memalloc_nofs_save();
> -
> ptr = __vmalloc(size, lflags);
>
> - if (flags & KM_NOFS)
> - memalloc_nofs_restore(nofs_flag);
> -
This breaks both kmem_alloc_large() and kmem_alloc_io() if they are
called from an explicit KM_NOFS context. vmalloc() does not respect
the gfp flags that are passed to it and will always do GFP_KERNEL
allocations deep down in the page table allocation code, and hence
we must use memalloc_nofs_save() here if called in a KM_NOFS
context.
> return ptr;
> }
>
> diff --git a/fs/xfs/kmem.h b/fs/xfs/kmem.h
> index 34cbcfd..ccc63de 100644
> --- a/fs/xfs/kmem.h
> +++ b/fs/xfs/kmem.h
> @@ -34,7 +34,7 @@
> BUG_ON(flags & ~(KM_NOFS | KM_MAYFAIL | KM_ZERO | KM_NOLOCKDEP));
>
> lflags = GFP_KERNEL | __GFP_NOWARN;
> - if (flags & KM_NOFS)
> + if (current->flags & PF_FSTRANS || flags & KM_NOFS)
> lflags &= ~__GFP_FS;
No. If we are in a transaction context, PF_MEMALLOC_NOFS should be
set. We got rid of all the PF_FSTRANS checks out of this code by
moving to PF_MEMALLOC_NOFS, reverting this isn't an improvement.
>
> /*
> diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
> index 2d25bab..65d0afe 100644
> --- a/fs/xfs/libxfs/xfs_btree.c
> +++ b/fs/xfs/libxfs/xfs_btree.c
> @@ -2814,7 +2814,7 @@ struct xfs_btree_split_args {
> struct xfs_btree_split_args *args = container_of(work,
> struct xfs_btree_split_args, work);
> unsigned long pflags;
> - unsigned long new_pflags = PF_MEMALLOC_NOFS;
> + unsigned long new_pflags = PF_FSTRANS;
new_pflags = PF_MEMALLOC_NOFS | PF_FSTRANS;
>
> /*
> * we are in a transaction context here, but may also be doing work
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index b356118..02733eb 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
> @@ -62,7 +62,7 @@ static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend)
> * We hand off the transaction to the completion thread now, so
> * clear the flag here.
> */
> - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
> + current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
current_restore_flags_nested(PF_MEMALLOC_NOFS | PF_FSTRANS);
> return 0;
> }
>
> @@ -125,7 +125,7 @@ static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend)
> * thus we need to mark ourselves as being in a transaction manually.
> * Similarly for freeze protection.
> */
> - current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
> + current_set_flags_nested(&tp->t_pflags, PF_FSTRANS);
current_set_flags_nested(PF_MEMALLOC_NOFS | PF_FSTRANS);
> __sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS);
>
> /* we abort the update if there was an IO error */
> diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
> index 9f70d2f..ab737fe 100644
> --- a/fs/xfs/xfs_linux.h
> +++ b/fs/xfs/xfs_linux.h
> @@ -102,12 +102,8 @@
> #define xfs_cowb_secs xfs_params.cowb_timer.val
>
> #define current_cpu() (raw_smp_processor_id())
> -#define current_pid() (current->pid)
> -#define current_test_flags(f) (current->flags & (f))
> #define current_set_flags_nested(sp, f) \
> (*(sp) = current->flags, current->flags |= (f))
> -#define current_clear_flags_nested(sp, f) \
> - (*(sp) = current->flags, current->flags &= ~(f))
> #define current_restore_flags_nested(sp, f) \
> (current->flags = ((current->flags & ~(f)) | (*(sp) & (f))))
Separate cleanup patch to remove unrelated definitions, please.
> diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> index 3c94e5f..1c1b982 100644
> --- a/fs/xfs/xfs_trans.c
> +++ b/fs/xfs/xfs_trans.c
> @@ -153,7 +153,7 @@
> bool rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0;
>
> /* Mark this thread as being in a transaction */
> - current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
> + current_set_flags_nested(&tp->t_pflags, PF_FSTRANS);
>
And, again, PF_FSTRANS | PF_MEMALLOC_NOFS through this code.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] xfs: reintroduce PF_FSTRANS for transaction reservation recursion protection
2020-06-21 23:04 ` Dave Chinner
@ 2020-06-22 12:18 ` Yafang Shao
0 siblings, 0 replies; 3+ messages in thread
From: Yafang Shao @ 2020-06-22 12:18 UTC (permalink / raw)
To: Dave Chinner
Cc: Michal Hocko, Darrick J. Wong, Christoph Hellwig, Andrew Morton,
Brian Foster, linux-xfs, linux-fsdevel, Linux MM
On Mon, Jun 22, 2020 at 7:04 AM Dave Chinner <david@fromorbit.com> wrote:
>
> On Sat, Jun 20, 2020 at 03:12:54AM -0400, Yafang Shao wrote:
> > PF_FSTRANS which is used to avoid transaction reservation recursion, is
> > dropped since commit 9070733b4efa ("xfs: abstract PF_FSTRANS to
> > PF_MEMALLOC_NOFS") and commit 7dea19f9ee63 ("mm: introduce
> > memalloc_nofs_{save,restore} API") and replaced by PF_MEMALLOC_NOFS which
> > means to avoid filesystem reclaim recursion. That change is subtle.
> > Let's take the exmple of the check of WARN_ON_ONCE(current->flags &
> > PF_MEMALLOC_NOFS)) to explain why this abstraction from PF_FSTRANS to
> > PF_MEMALLOC_NOFS is not proper.
> >
> > Bellow comment is quoted from Dave,
> > > It wasn't for memory allocation recursion protection in XFS - it was for
> > > transaction reservation recursion protection by something trying to flush
> > > data pages while holding a transaction reservation. Doing
> > > this could deadlock the journal because the existing reservation
> > > could prevent the nested reservation for being able to reserve space
> > > in the journal and that is a self-deadlock vector.
> > > IOWs, this check is not protecting against memory reclaim recursion
> > > bugs at all (that's the previous check [1]). This check is
> > > protecting against the filesystem calling writepages directly from a
> > > context where it can self-deadlock.
> > > So what we are seeing here is that the PF_FSTRANS ->
> > > PF_MEMALLOC_NOFS abstraction lost all the actual useful information
> > > about what type of error this check was protecting against.
> >
> > Besides reintroducing PF_FSTRANS, there're some other improvements in this
> > patch,
> > - Remove useless MACRO current_clear_flags_nested(), current_pid() and
> > current_test_flags().
> > - Remove useless memalloc_nofs_{save, restore} in __kmem_vmalloc()
> >
> > [1]. Bellow check is to avoid memory reclaim recursion.
> > if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
> > PF_MEMALLOC))
> > goto redirty;
> >
> > Cc: Dave Chinner <david@fromorbit.com>
> > Cc: Michal Hocko <mhocko@kernel.org>
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > ---
> > fs/iomap/buffered-io.c | 4 ++--
> > fs/xfs/kmem.c | 7 -------
> > fs/xfs/kmem.h | 2 +-
> > fs/xfs/libxfs/xfs_btree.c | 2 +-
> > fs/xfs/xfs_aops.c | 4 ++--
> > fs/xfs/xfs_linux.h | 4 ----
> > fs/xfs/xfs_trans.c | 12 ++++++------
> > include/linux/sched.h | 1 +
> > 8 files changed, 13 insertions(+), 23 deletions(-)
> >
> > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > index bcfc288..0f1945c 100644
> > --- a/fs/iomap/buffered-io.c
> > +++ b/fs/iomap/buffered-io.c
> > @@ -1500,9 +1500,9 @@ static void iomap_writepage_end_bio(struct bio *bio)
> >
> > /*
> > * Given that we do not allow direct reclaim to call us, we should
> > - * never be called in a recursive filesystem reclaim context.
> > + * never be called while in a filesystem transaction.
> > */
> > - if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS))
> > + if (WARN_ON_ONCE(current->flags & PF_FSTRANS))
> > goto redirty;
>
> This is OK, but the rest of the patch is not.
>
> I did not say "replace all XFS use of GFP_NOFS/KM_NOFS with
> PF_TRANS", which is what this patch does. The use of
> PF_MEMALLOC_NOFS within transactions is correct and valid and needs
> to remain. Replacing this with PF_FSTRANS effectively reverts all
> the simplifications and obviously self-documneting code that
> PF_MEMALLOC_NOFS provides us with.
>
Sorry about that, I misunderstood it. Will correct it in the next version.
> IOWs, PF_MEMALLOC_NOFS is used to indicate that this is a "no
> reclaim recursion" path and so it's use remains completely unchanged
> in XFS. PF_FSTRANS is to indicate this is a "no
> transaction recursion" path, which is a different thing and needs
> it's own specific annotation.
>
Thanks for the explanation.
> > diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
> > index f136647..9875a23 100644
> > --- a/fs/xfs/kmem.c
> > +++ b/fs/xfs/kmem.c
> > @@ -41,18 +41,11 @@
> > static void *
> > __kmem_vmalloc(size_t size, xfs_km_flags_t flags)
> > {
> > - unsigned nofs_flag = 0;
> > void *ptr;
> > gfp_t lflags = kmem_flags_convert(flags);
> >
> > - if (flags & KM_NOFS)
> > - nofs_flag = memalloc_nofs_save();
> > -
> > ptr = __vmalloc(size, lflags);
> >
> > - if (flags & KM_NOFS)
> > - memalloc_nofs_restore(nofs_flag);
> > -
>
> This breaks both kmem_alloc_large() and kmem_alloc_io() if they are
> called from an explicit KM_NOFS context. vmalloc() does not respect
> the gfp flags that are passed to it and will always do GFP_KERNEL
> allocations deep down in the page table allocation code, and hence
> we must use memalloc_nofs_save() here if called in a KM_NOFS
> context.
>
I thought kmem_flags_convert() has already checked KM_NOFS so we don't
need to call memalloc_nofs_save(), but it seems I was wrong.
Thanks for the clarification.
> > return ptr;
> > }
> >
> > diff --git a/fs/xfs/kmem.h b/fs/xfs/kmem.h
> > index 34cbcfd..ccc63de 100644
> > --- a/fs/xfs/kmem.h
> > +++ b/fs/xfs/kmem.h
> > @@ -34,7 +34,7 @@
> > BUG_ON(flags & ~(KM_NOFS | KM_MAYFAIL | KM_ZERO | KM_NOLOCKDEP));
> >
> > lflags = GFP_KERNEL | __GFP_NOWARN;
> > - if (flags & KM_NOFS)
> > + if (current->flags & PF_FSTRANS || flags & KM_NOFS)
> > lflags &= ~__GFP_FS;
>
> No. If we are in a transaction context, PF_MEMALLOC_NOFS should be
> set. We got rid of all the PF_FSTRANS checks out of this code by
> moving to PF_MEMALLOC_NOFS, reverting this isn't an improvement.
>
Got it. Thanks.
> >
> > /*
> > diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
> > index 2d25bab..65d0afe 100644
> > --- a/fs/xfs/libxfs/xfs_btree.c
> > +++ b/fs/xfs/libxfs/xfs_btree.c
> > @@ -2814,7 +2814,7 @@ struct xfs_btree_split_args {
> > struct xfs_btree_split_args *args = container_of(work,
> > struct xfs_btree_split_args, work);
> > unsigned long pflags;
> > - unsigned long new_pflags = PF_MEMALLOC_NOFS;
> > + unsigned long new_pflags = PF_FSTRANS;
>
> new_pflags = PF_MEMALLOC_NOFS | PF_FSTRANS;
> >
> > /*
> > * we are in a transaction context here, but may also be doing work
> > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> > index b356118..02733eb 100644
> > --- a/fs/xfs/xfs_aops.c
> > +++ b/fs/xfs/xfs_aops.c
> > @@ -62,7 +62,7 @@ static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend)
> > * We hand off the transaction to the completion thread now, so
> > * clear the flag here.
> > */
> > - current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
> > + current_restore_flags_nested(&tp->t_pflags, PF_FSTRANS);
>
> current_restore_flags_nested(PF_MEMALLOC_NOFS | PF_FSTRANS);
>
Thanks
> > return 0;
> > }
> >
> > @@ -125,7 +125,7 @@ static inline bool xfs_ioend_is_append(struct iomap_ioend *ioend)
> > * thus we need to mark ourselves as being in a transaction manually.
> > * Similarly for freeze protection.
> > */
> > - current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
> > + current_set_flags_nested(&tp->t_pflags, PF_FSTRANS);
>
> current_set_flags_nested(PF_MEMALLOC_NOFS | PF_FSTRANS);
>
Thanks
> > __sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS);
> >
> > /* we abort the update if there was an IO error */
> > diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
> > index 9f70d2f..ab737fe 100644
> > --- a/fs/xfs/xfs_linux.h
> > +++ b/fs/xfs/xfs_linux.h
> > @@ -102,12 +102,8 @@
> > #define xfs_cowb_secs xfs_params.cowb_timer.val
> >
> > #define current_cpu() (raw_smp_processor_id())
> > -#define current_pid() (current->pid)
> > -#define current_test_flags(f) (current->flags & (f))
> > #define current_set_flags_nested(sp, f) \
> > (*(sp) = current->flags, current->flags |= (f))
> > -#define current_clear_flags_nested(sp, f) \
> > - (*(sp) = current->flags, current->flags &= ~(f))
> > #define current_restore_flags_nested(sp, f) \
> > (current->flags = ((current->flags & ~(f)) | (*(sp) & (f))))
>
> Separate cleanup patch to remove unrelated definitions, please.
>
Sure, I will.
> > diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
> > index 3c94e5f..1c1b982 100644
> > --- a/fs/xfs/xfs_trans.c
> > +++ b/fs/xfs/xfs_trans.c
> > @@ -153,7 +153,7 @@
> > bool rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0;
> >
> > /* Mark this thread as being in a transaction */
> > - current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
> > + current_set_flags_nested(&tp->t_pflags, PF_FSTRANS);
> >
>
> And, again, PF_FSTRANS | PF_MEMALLOC_NOFS through this code.
>
Thanks
--
Thanks
Yafang
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-06-22 12:18 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2020-06-20 7:12 [PATCH] xfs: reintroduce PF_FSTRANS for transaction reservation recursion protection Yafang Shao
2020-06-21 23:04 ` Dave Chinner
2020-06-22 12:18 ` Yafang Shao
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