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| author | Eric Ren <zren@suse.com> | 2016-09-30 15:11:32 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-09-30 15:26:52 -0700 |
| commit | c33f0785bf292cf1d15f4fbe42869c63e205b21c (patch) | |
| tree | eb73b7096ef554702a66b8d37f1dbc5fdd419702 | |
| parent | 22f2ac51b6d643666f4db093f13144f773ff3f3a (diff) | |
| download | linux-c33f0785bf292cf1d15f4fbe42869c63e205b21c.tar.bz2 | |
ocfs2: fix deadlock on mmapped page in ocfs2_write_begin_nolock()
The testcase "mmaptruncate" of ocfs2-test deadlocks occasionally.
In this testcase, we create a 2*CLUSTER_SIZE file and mmap() on it;
there are 2 process repeatedly performing the following operations
respectively: one is doing memset(mmaped_addr + 2*CLUSTER_SIZE - 1, 'a',
1), while the another is playing ftruncate(fd, 2*CLUSTER_SIZE) and then
ftruncate(fd, CLUSTER_SIZE) again and again.
This is the backtrace when the deadlock happens:
__wait_on_bit_lock+0x50/0xa0
__lock_page+0xb7/0xc0
ocfs2_write_begin_nolock+0x163f/0x1790 [ocfs2]
ocfs2_page_mkwrite+0x1c7/0x2a0 [ocfs2]
do_page_mkwrite+0x66/0xc0
handle_mm_fault+0x685/0x1350
__do_page_fault+0x1d8/0x4d0
trace_do_page_fault+0x37/0xf0
do_async_page_fault+0x19/0x70
async_page_fault+0x28/0x30
In ocfs2_write_begin_nolock(), we first grab the pages and then allocate
disk space for this write; ocfs2_try_to_free_truncate_log() will be
called if -ENOSPC is returned; if we're lucky to get enough clusters,
which is usually the case, we start over again.
But in ocfs2_free_write_ctxt() the target page isn't unlocked, so we
will deadlock when trying to grab the target page again.
Also, -ENOMEM might be returned in ocfs2_grab_pages_for_write().
Another deadlock will happen in __do_page_mkwrite() if
ocfs2_page_mkwrite() returns non-VM_FAULT_LOCKED, and along with a
locked target page.
These two errors fail on the same path, so fix them by unlocking the
target page manually before ocfs2_free_write_ctxt().
Jan Kara helps me clear out the JBD2 part, and suggest the hint for root
cause.
Changes since v1:
1. Also put ENOMEM error case into consideration.
Link: http://lkml.kernel.org/r/1474173902-32075-1-git-send-email-zren@suse.com
Signed-off-by: Eric Ren <zren@suse.com>
Reviewed-by: He Gang <ghe@suse.com>
Acked-by: Joseph Qi <joseph.qi@huawei.com>
Cc: Mark Fasheh <mfasheh@suse.de>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | fs/ocfs2/aops.c | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c index 98d36548153d..bbb4b3e5b4ff 100644 --- a/fs/ocfs2/aops.c +++ b/fs/ocfs2/aops.c @@ -1842,6 +1842,16 @@ out_commit: ocfs2_commit_trans(osb, handle); out: + /* + * The mmapped page won't be unlocked in ocfs2_free_write_ctxt(), + * even in case of error here like ENOSPC and ENOMEM. So, we need + * to unlock the target page manually to prevent deadlocks when + * retrying again on ENOSPC, or when returning non-VM_FAULT_LOCKED + * to VM code. + */ + if (wc->w_target_locked) + unlock_page(mmap_page); + ocfs2_free_write_ctxt(inode, wc); if (data_ac) { |