| Message ID | 20200726145726.1484-1-laoar.shao@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] xfs: introduce task->in_fstrans for transaction reservation recursion protection | expand |
On Sun, Jul 26, 2020 at 10:57:26AM -0400, Yafang Shao wrote: > Bellow comment is quoted from Dave, FYI, you mean "Below", not "Bellow". Dave doesn't often bellow. > 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. I don't think we need a new flag for this. I think you can just set current->journal_info to a non-NULL value. > +++ 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; > +} Does XFS support nested transactions? If we're just using current->journal_info, we can pretend its an unsigned long and use it as a counter rather than handle the nesting the same way as the GFP flags.
On Sun, Jul 26, 2020 at 05:04:00PM +0100, Matthew Wilcox wrote: > On Sun, Jul 26, 2020 at 10:57:26AM -0400, Yafang Shao wrote: > > Bellow comment is quoted from Dave, > > FYI, you mean "Below", not "Bellow". Dave doesn't often bellow. > > > 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. > > I don't think we need a new flag for this. I think you can just set > current->journal_info to a non-NULL value. > > > +++ 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; > > +} > > Does XFS support nested transactions? If we're just using > current->journal_info, we can pretend its an unsigned long and use it > as a counter rather than handle the nesting the same way as the GFP flags. Not currently. --D
On Mon, Jul 27, 2020 at 12:04 AM Matthew Wilcox <willy@infradead.org> wrote: > > On Sun, Jul 26, 2020 at 10:57:26AM -0400, Yafang Shao wrote: > > Bellow comment is quoted from Dave, > > FYI, you mean "Below", not "Bellow". Dave doesn't often bellow. Ah, thanks for pointing that out. I often make that kind of misstake. > > > 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. > > I don't think we need a new flag for this. I think you can just set > current->journal_info to a non-NULL value. Seems like a good suggestion. I will think about it. > > > +++ 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; > > +} > > Does XFS support nested transactions? If we're just using > current->journal_info, we can pretend its an unsigned long and use it > as a counter rather than handle the nesting the same way as the GFP flags. >
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. */
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@gmail.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Darrick J. Wong <darrick.wong@oracle.com> Cc: Matthew Wilcox <willy@infradead.org> --- 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(-)