linux-ext4 - [PATCH] ext4: call ext4_ioend_wait and ext4_flush_completed_IO in ext4_evict

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Message-Id: <20110812023105.18FBB4207C@ruihe.smo.corp.google.com>
Date:	Thu, 11 Aug 2011 19:31:04 -0700 (PDT)
From:	jiayingz@...gle.com (Jiaying Zhang)
To:	tytso@....edu
Cc:	linux-ext4@...r.kernel.org
Subject: [PATCH] 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@...gle.com>
---
 fs/ext4/inode.c |    6 ++++++
 fs/ext4/super.c |    1 -
 2 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index de50b16..2aba49e 100644
--- a/fs/ext4/inode.c
+++ b/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) {
 		truncate_inode_pages(&inode->i_data, 0);
 		goto no_delete;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 9ea71aa..111ed9d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -892,7 +892,6 @@ 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!",
-- 
1.7.3.1

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