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authorEric Ren <zren@suse.com>2016-09-30 15:11:32 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-09-30 15:26:52 -0700
commitc33f0785bf292cf1d15f4fbe42869c63e205b21c (patch)
treeeb73b7096ef554702a66b8d37f1dbc5fdd419702
parent22f2ac51b6d643666f4db093f13144f773ff3f3a (diff)
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.c10
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) {

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