From 8c0bec2151a47906bf779c6715a10ce04453ab77 Mon Sep 17 00:00:00 2001 From: Jiaying Zhang Date: Wed, 31 Aug 2011 11:50:51 -0400 Subject: 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 Signed-off-by: "Theodore Ts'o" --- fs/ext4/page-io.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) (limited to 'fs/ext4/page-io.c') 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); -- cgit v1.2.1