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Sat, 01 Aug 2020 08:47:11 -0700 (PDT) Received: from localhost.localdomain ([203.100.54.194]) by smtp.gmail.com with ESMTPSA id j26sm13717331pfe.200.2020.08.01.08.47.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 01 Aug 2020 08:47:10 -0700 (PDT) From: Yafang Shao To: david@fromorbit.com, hch@infradead.org, darrick.wong@oracle.com, mhocko@kernel.org, willy@infradead.org Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Yafang Shao Subject: [PATCH v4 2/2] xfs: avoid transaction reservation recursion Date: Sat, 1 Aug 2020 11:46:32 -0400 Message-Id: <20200801154632.866356-3-laoar.shao@gmail.com> X-Mailer: git-send-email 2.18.1 In-Reply-To: <20200801154632.866356-1-laoar.shao@gmail.com> References: <20200801154632.866356-1-laoar.shao@gmail.com> X-Rspamd-Queue-Id: AB98810097AA4 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: 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. Below 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. As current->journal_info isn't used in XFS, we can reuse it to indicate whehter the task is in fstrans or not. [1]. Below 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 Cc: Dave Chinner Cc: Christoph Hellwig Cc: Michal Hocko Cc: Darrick J. Wong Cc: Matthew Wilcox --- fs/iomap/buffered-io.c | 4 ++-- fs/xfs/libxfs/xfs_btree.c | 2 ++ fs/xfs/xfs_aops.c | 3 +++ fs/xfs/xfs_linux.h | 19 +++++++++++++++++++ fs/xfs/xfs_trans.c | 8 +++++++- 5 files changed, 33 insertions(+), 3 deletions(-) diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index bcfc288dba3f..b3f66b6b5116 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->journal_info)) goto redirty; /* diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c index 2d25bab68764..0795511f9e6a 100644 --- a/fs/xfs/libxfs/xfs_btree.c +++ b/fs/xfs/libxfs/xfs_btree.c @@ -2825,6 +2825,7 @@ xfs_btree_split_worker( if (args->kswapd) new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; + xfs_trans_context_start(); current_set_flags_nested(&pflags, new_pflags); args->result = __xfs_btree_split(args->cur, args->level, args->ptrp, @@ -2832,6 +2833,7 @@ xfs_btree_split_worker( complete(args->done); current_restore_flags_nested(&pflags, new_pflags); + xfs_trans_context_end(); } /* diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c index b35611882ff9..39ef95acdd8e 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(); + 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. */ + 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..1192b660a968 100644 --- a/fs/xfs/xfs_linux.h +++ b/fs/xfs/xfs_linux.h @@ -111,6 +111,25 @@ typedef __u32 xfs_nlink_t; #define current_restore_flags_nested(sp, f) \ (current->flags = ((current->flags & ~(f)) | (*(sp) & (f)))) +static inline void xfs_trans_context_start(void) +{ + long flags = (long)current->journal_info; + + /* + * Reuse journal_info to indicate whehter the current is in fstrans + * or not. + */ + current->journal_info = (void *)(flags + 1); +} + +static inline void xfs_trans_context_end(void) +{ + long flags = (long)current->journal_info; + + WARN_ON_ONCE(flags <= 0); + current->journal_info = ((void *)(flags - 1)); +} + #define NBBY 8 /* number of bits per byte */ /* diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c index 9ff41970d0c7..38d94679ad41 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 */ + xfs_trans_context_start(); current_set_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); /* @@ -859,6 +860,7 @@ __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(); xfs_trans_free(tp); /* @@ -891,6 +893,7 @@ __xfs_trans_commit( tp->t_ticket = NULL; } current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); + xfs_trans_context_end(); xfs_trans_free_items(tp, !!error); xfs_trans_free(tp); @@ -952,6 +955,7 @@ 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(); xfs_trans_free_items(tp, dirty); xfs_trans_free(tp); @@ -1005,8 +1009,10 @@ xfs_trans_roll( tres.tr_logflags = XFS_TRANS_PERM_LOG_RES; tp = *tpp; error = xfs_trans_reserve(tp, &tres, 0, 0); - if (error) + if (error) { current_restore_flags_nested(&tp->t_pflags, PF_MEMALLOC_NOFS); + xfs_trans_context_end(); + } return error; }