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author | Jiaying Zhang <jiayingz@google.com> | 2011-08-31 17:50:51 +0200 |
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committer | Theodore Ts'o <tytso@mit.edu> | 2011-08-31 17:50:51 +0200 |
commit | 8c0bec2151a47906bf779c6715a10ce04453ab77 (patch) | |
tree | 0165e80ba408b5db1e9e2adf9264bf4186b06768 /fs/ext4/page-io.c | |
parent | Linux 3.1-rc3 (diff) | |
download | linux-8c0bec2151a47906bf779c6715a10ce04453ab77.tar.xz linux-8c0bec2151a47906bf779c6715a10ce04453ab77.zip |
ext4: remove i_mutex lock in ext4_evict_inode to fix lockdep complaining
The i_mutex lock and flush_completed_IO() added by commit 2581fdc810
in ext4_evict_inode() causes lockdep complaining about potential
deadlock in several places. In most/all of these LOCKDEP complaints
it looks like it's a false positive, since many of the potential
circular locking cases can't take place by the time the
ext4_evict_inode() is called; but since at the very least it may mask
real problems, we need to address this.
This change removes the flush_completed_IO() and i_mutex lock in
ext4_evict_inode(). Instead, we take a different approach to resolve
the software lockup that commit 2581fdc810 intends to fix. Rather
than having ext4-dio-unwritten thread wait for grabing the i_mutex
lock of an inode, we use mutex_trylock() instead, and simply requeue
the work item if we fail to grab the inode's i_mutex lock.
This should speed up work queue processing in general and also
prevents the following deadlock scenario: During page fault,
shrink_icache_memory is called that in turn evicts another inode B.
Inode B has some pending io_end work so it calls ext4_ioend_wait()
that waits for inode B's i_ioend_count to become zero. However, inode
B's ioend work was queued behind some of inode A's ioend work on the
same cpu's ext4-dio-unwritten workqueue. As the ext4-dio-unwritten
thread on that cpu is processing inode A's ioend work, it tries to
grab inode A's i_mutex lock. Since the i_mutex lock of inode A is
still hold before the page fault happened, we enter a deadlock.
Signed-off-by: Jiaying Zhang <jiayingz@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Diffstat (limited to '')
-rw-r--r-- | fs/ext4/page-io.c | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c index 78839af7ce29..92f38ee13f8a 100644 --- a/fs/ext4/page-io.c +++ b/fs/ext4/page-io.c @@ -142,7 +142,23 @@ static void ext4_end_io_work(struct work_struct *work) unsigned long flags; int ret; - mutex_lock(&inode->i_mutex); + if (!mutex_trylock(&inode->i_mutex)) { + /* + * Requeue the work instead of waiting so that the work + * items queued after this can be processed. + */ + queue_work(EXT4_SB(inode->i_sb)->dio_unwritten_wq, &io->work); + /* + * To prevent the ext4-dio-unwritten thread from keeping + * requeueing end_io requests and occupying cpu for too long, + * yield the cpu if it sees an end_io request that has already + * been requeued. + */ + if (io->flag & EXT4_IO_END_QUEUED) + yield(); + io->flag |= EXT4_IO_END_QUEUED; + return; + } ret = ext4_end_io_nolock(io); if (ret < 0) { mutex_unlock(&inode->i_mutex); |