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.
[1]. Bellow check is to avoid memory reclaim recursion.
if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
PF_MEMALLOC))
goto redirty;
Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx>
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
---
fs/iomap/buffered-io.c | 4 ++--
fs/xfs/libxfs/xfs_btree.c | 2 +-
fs/xfs/xfs_aops.c | 4 ++--
fs/xfs/xfs_trans.c | 12 ++++++------
include/linux/sched.h | 1 +
5 files changed, 12 insertions(+), 11 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/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
index 2d25bab..4a7c8b7 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_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..79da028 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_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_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_trans.c b/fs/xfs/xfs_trans.c
index 3c94e5f..011f52f 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_MEMALLOC_NOFS | 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_MEMALLOC_NOFS | 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_MEMALLOC_NOFS | 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_MEMALLOC_NOFS | 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_MEMALLOC_NOFS | 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_MEMALLOC_NOFS | 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
