ext4: call ext4_ioend_wait and ext4_flush_completed_IO in ext4_evict_inode

Flush inode's i_completed_io_list before calling ext4_io_wait to
prevent the following deadlock scenario: A page fault happens while
some process is writing inode A. 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.

Also moves ext4_flush_completed_IO and ext4_ioend_wait from
ext4_destroy_inode() to ext4_evict_inode(). During inode deleteion,
ext4_evict_inode() is called before ext4_destroy_inode() and in
ext4_evict_inode(), we may call ext4_truncate() without holding
i_mutex lock. As a result, there is a race between flush_completed_IO
that is called from ext4_ext_truncate() and ext4_end_io_work, which
may cause corruption on an io_end structure. This change moves
ext4_flush_completed_IO and ext4_ioend_wait from ext4_destroy_inode()
to ext4_evict_inode() to resolve the race between ext4_truncate() and
ext4_end_io_work during inode deletion.
Signed-off-by: Jiaying Zhang <jiayingz@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org

fs/ext4/inode.c

@@ -120,6 +120,12 @@ void ext4_evict_inode(struct inode *inode)
 	int err;
 
 	trace_ext4_evict_inode(inode);
+
+	mutex_lock(&inode->i_mutex);
+	ext4_flush_completed_IO(inode);
+	mutex_unlock(&inode->i_mutex);
+	ext4_ioend_wait(inode);
+
 	if (inode->i_nlink) {
 		/*
 		 * When journalling data dirty buffers are tracked only in the

fs/ext4/super.c

@@ -919,7 +919,6 @@ static void ext4_i_callback(struct rcu_head *head)
 
 static void ext4_destroy_inode(struct inode *inode)
 {
-	ext4_ioend_wait(inode);
 	if (!list_empty(&(EXT4_I(inode)->i_orphan))) {
 		ext4_msg(inode->i_sb, KERN_ERR,
 			 "Inode %lu (%p): orphan list check failed!",