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.
As a result, we should reintroduce PF_FSTRANS. Because PF_FSTRANS is only
set by current, we can move it out of task->flags to avoid being out of PF_
flags. So a new flag in_fstrans is introduced.
[1]. Bellow check is to avoid memory reclaim recursion.
if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) ==
PF_MEMALLOC))
goto redirty;
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
---
v2 -> v3:
- retitle from "xfs: reintroduce PF_FSTRANS for transaction reservation recursion protection"
- replace PF_FSTRANS with in_fstrans, per Christoph.
---
fs/iomap/buffered-io.c | 4 ++--
fs/xfs/libxfs/xfs_btree.c | 3 +++
fs/xfs/xfs_aops.c | 3 +++
fs/xfs/xfs_linux.h | 14 ++++++++++++++
fs/xfs/xfs_trans.c | 7 +++++++
fs/xfs/xfs_trans.h | 1 +
include/linux/sched.h | 2 ++
7 files changed, 32 insertions(+), 2 deletions(-)
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index bcfc288dba3f..a90d865fb435 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1500,9 +1500,9 @@ iomap_do_writepage(struct page *page, struct writeback_control *wbc, void *data)
/*
* 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->in_fstrans))
goto redirty;
/*
diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
index 2d25bab68764..7f55ab17d5dd 100644
--- a/fs/xfs/libxfs/xfs_btree.c
+++ b/fs/xfs/libxfs/xfs_btree.c
@@ -2815,6 +2815,7 @@ xfs_btree_split_worker(
struct xfs_btree_split_args, work);
unsigned long pflags;
unsigned long new_pflags = PF_MEMALLOC_NOFS;
+ unsigned int in_fstrans;
/*
* we are in a transaction context here, but may also be doing work
@@ -2825,6 +2826,7 @@ xfs_btree_split_worker(
if (args->kswapd)
new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
+ in_fstrans = xfs_trans_context_start();
current_set_flags_nested(&pflags, new_pflags);
args->result = __xfs_btree_split(args->cur, args->level, args->ptrp,
@@ -2832,6 +2834,7 @@ xfs_btree_split_worker(
complete(args->done);
current_restore_flags_nested(&pflags, new_pflags);
+ xfs_trans_context_end(in_fstrans);
}
/*
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index b35611882ff9..65fc997159fa 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -63,6 +63,8 @@ xfs_setfilesize_trans_alloc(
* clear the flag here.
*/
current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ xfs_trans_context_end(tp->t_fstrans);
+
return 0;
}
@@ -125,6 +127,7 @@ xfs_setfilesize_ioend(
* thus we need to mark ourselves as being in a transaction manually.
* Similarly for freeze protection.
*/
+ tp->t_fstrans = xfs_trans_context_start();
current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
__sb_writers_acquired(VFS_I(ip)->i_sb, SB_FREEZE_FS);
diff --git a/fs/xfs/xfs_linux.h b/fs/xfs/xfs_linux.h
index 9f70d2f68e05..5cee22b1674f 100644
--- a/fs/xfs/xfs_linux.h
+++ b/fs/xfs/xfs_linux.h
@@ -111,6 +111,20 @@ typedef __u32 xfs_nlink_t;
#define current_restore_flags_nested(sp, f) \
(current->flags = ((current->flags & ~(f)) | (*(sp) & (f))))
+static inline unsigned int xfs_trans_context_start(void)
+{
+ unsigned int flags = current->in_fstrans;
+
+ current->in_fstrans = 1;
+
+ return flags;
+}
+
+static inline void xfs_trans_context_end(unsigned int flags)
+{
+ current->in_fstrans = flags ? 1 : 0;
+}
+
#define NBBY 8 /* number of bits per byte */
/*
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 3c94e5ff4316..8936c650abc9 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -153,6 +153,7 @@ xfs_trans_reserve(
bool rsvd = (tp->t_flags & XFS_TRANS_RESERVE) != 0;
/* Mark this thread as being in a transaction */
+ tp->t_fstrans = xfs_trans_context_start();
current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
/*
@@ -164,6 +165,7 @@ xfs_trans_reserve(
error = xfs_mod_fdblocks(mp, -((int64_t)blocks), rsvd);
if (error != 0) {
current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ xfs_trans_context_end(tp->t_fstrans);
return -ENOSPC;
}
tp->t_blk_res += blocks;
@@ -241,6 +243,7 @@ xfs_trans_reserve(
}
current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ xfs_trans_context_end(tp->t_fstrans);
return error;
}
@@ -862,6 +865,7 @@ __xfs_trans_commit(
xfs_log_commit_cil(mp, tp, &commit_lsn, regrant);
current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ xfs_trans_context_end(tp->t_fstrans);
xfs_trans_free(tp);
/*
@@ -893,7 +897,9 @@ __xfs_trans_commit(
xfs_log_ticket_ungrant(mp->m_log, tp->t_ticket);
tp->t_ticket = NULL;
}
+
current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ xfs_trans_context_end(tp->t_fstrans);
xfs_trans_free_items(tp, !!error);
xfs_trans_free(tp);
@@ -955,6 +961,7 @@ xfs_trans_cancel(
/* mark this thread as no longer being in a transaction */
current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS);
+ xfs_trans_context_end(tp->t_fstrans);
xfs_trans_free_items(tp, dirty);
xfs_trans_free(tp);
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index 8308bf6d7e40..eeb307536efe 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -118,6 +118,7 @@ typedef struct xfs_trans {
unsigned int t_rtx_res; /* # of rt extents resvd */
unsigned int t_rtx_res_used; /* # of resvd rt extents used */
unsigned int t_flags; /* misc flags */
+ unsigned int t_fstrans; /* saved fstrans state */
xfs_fsblock_t t_firstblock; /* first block allocated */
struct xlog_ticket *t_ticket; /* log mgr ticket */
struct xfs_mount *t_mountp; /* ptr to fs mount struct */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 692e327d7455..82a0a3999cbb 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -800,6 +800,8 @@ struct task_struct {
/* Stalled due to lack of memory */
unsigned in_memstall:1;
#endif
+ /* Inside a filesystem transaction */
+ unsigned in_fstrans:1;
unsigned long atomic_flags; /* Flags requiring atomic access. */
--
2.18.1
