Patch "ext4: fix race between truncate and __ext4_journalled_writepage()" has been added to the 3.10-stable tree

This is a note to let you know that I've just added the patch titled

ext4: fix race between truncate and __ext4_journalled_writepage()

to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ext4-fix-race-between-truncate-and-__ext4_journalled_writepage.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Theodore Ts'o <[email protected]>
Date: Fri, 12 Jun 2015 23:45:33 -0400
Subject: ext4: fix race between truncate and __ext4_journalled_writepage()

From: Theodore Ts'o <[email protected]>

commit bdf96838aea6a265f2ae6cbcfb12a778c84a0b8e upstream.

The commit cf108bca465d: "ext4: Invert the locking order of page_lock and transaction start" caused __ext4_journalled_writepage() to drop the page lock before the page was written back, as part of changing the locking order to jbd2_journal_start -> page_lock. However, this introduced a potential race if there was a truncate racing with the data=journalled writeback mode.

Fix this by grabbing the page lock after starting the journal handle, and then checking to see if page had gotten truncated out from under us.

This fixes a number of different warnings or BUG_ON's when running xfstests generic/086 in data=journalled mode, including:

jbd2_journal_dirty_metadata: vdc-8: bad jh for block 115643: transaction (ee3fe7 c0, 164), jh->b_transaction ( (null), 0), jh->b_next_transaction ( (null), 0), jlist 0

- and -

kernel BUG at /usr/projects/linux/ext4/fs/jbd2/transaction.c:2200!

    ...
Call Trace:
 [<c02b2ded>] ? __ext4_journalled_invalidatepage+0x117/0x117
 [<c02b2de5>] __ext4_journalled_invalidatepage+0x10f/0x117
 [<c02b2ded>] ? __ext4_journalled_invalidatepage+0x117/0x117
 [<c027d883>] ? lock_buffer+0x36/0x36
 [<c02b2dfa>] ext4_journalled_invalidatepage+0xd/0x22
 [<c0229139>] do_invalidatepage+0x22/0x26
 [<c0229198>] truncate_inode_page+0x5b/0x85
 [<c022934b>] truncate_inode_pages_range+0x156/0x38c
 [<c0229592>] truncate_inode_pages+0x11/0x15
 [<c022962d>] truncate_pagecache+0x55/0x71
 [<c02b913b>] ext4_setattr+0x4a9/0x560
 [<c01ca542>] ? current_kernel_time+0x10/0x44
 [<c026c4d8>] notify_change+0x1c7/0x2be
 [<c0256a00>] do_truncate+0x65/0x85
 [<c0226f31>] ? file_ra_state_init+0x12/0x29

- and -

WARNING: CPU: 1 PID: 1331 at /usr/projects/linux/ext4/fs/jbd2/transaction.c:1396
irty_metadata+0x14a/0x1ae()
    ...
Call Trace:
 [<c01b879f>] ? console_unlock+0x3a1/0x3ce
 [<c082cbb4>] dump_stack+0x48/0x60
 [<c0178b65>] warn_slowpath_common+0x89/0xa0
 [<c02ef2cf>] ? jbd2_journal_dirty_metadata+0x14a/0x1ae
 [<c0178bef>] warn_slowpath_null+0x14/0x18
 [<c02ef2cf>] jbd2_journal_dirty_metadata+0x14a/0x1ae
 [<c02d8615>] __ext4_handle_dirty_metadata+0xd4/0x19d
 [<c02b2f44>] write_end_fn+0x40/0x53
 [<c02b4a16>] ext4_walk_page_buffers+0x4e/0x6a
 [<c02b59e7>] ext4_writepage+0x354/0x3b8
 [<c02b2f04>] ? mpage_release_unused_pages+0xd4/0xd4
 [<c02b1b21>] ? wait_on_buffer+0x2c/0x2c
 [<c02b5a4b>] ? ext4_writepage+0x3b8/0x3b8
 [<c02b5a5b>] __writepage+0x10/0x2e
 [<c0225956>] write_cache_pages+0x22d/0x32c
 [<c02b5a4b>] ? ext4_writepage+0x3b8/0x3b8
 [<c02b6ee8>] ext4_writepages+0x102/0x607
 [<c019adfe>] ? sched_clock_local+0x10/0x10e
 [<c01a8a7c>] ? __lock_is_held+0x2e/0x44
 [<c01a8ad5>] ? lock_is_held+0x43/0x51
 [<c0226dff>] do_writepages+0x1c/0x29
 [<c0276bed>] __writeback_single_inode+0xc3/0x545
 [<c0277c07>] writeback_sb_inodes+0x21f/0x36d
    ...

---
 fs/ext4/inode.c |   23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

@@ -2099,19 +2099,32 @@ static int __ext4_journalled_writepage(s
 		ext4_walk_page_buffers(handle, page_bufs, 0, len,
 				       NULL, bget_one);
 	}
-	/* As soon as we unlock the page, it can go away, but we have
-	 * references to buffers so we are safe */
+	/*
+	 * We need to release the page lock before we start the
+	 * journal, so grab a reference so the page won't disappear
+	 * out from under us.
+	 */
+	get_page(page);
 	unlock_page(page);
 
 	handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE,
 				    ext4_writepage_trans_blocks(inode));
 	if (IS_ERR(handle)) {
 		ret = PTR_ERR(handle);
-		goto out;
+		put_page(page);
+		goto out_no_pagelock;
 	}
-
 	BUG_ON(!ext4_handle_valid(handle));
 
+	lock_page(page);
+	put_page(page);
+	if (page->mapping != mapping) {
+		/* The page got truncated from under us */
+		ext4_journal_stop(handle);
+		ret = 0;
+		goto out;
+	}
+
 	if (inline_data) {
 		ret = ext4_journal_get_write_access(handle, inode_bh);
 

@@ -2136,6 +2149,8 @@ static int __ext4_journalled_writepage(s
 				       NULL, bput_one);
 	ext4_set_inode_state(inode, EXT4_STATE_JDATA);
 out:
+	unlock_page(page);
+out_no_pagelock:
 	brelse(inode_bh);
 	return ret;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-3.10/ext4-correctly-migrate-a-file-with-a-hole-at-the-beginning.patch queue-3.10/jbd2-fix-ocfs2-corrupt-when-updating-journal-superblock-fails.patch queue-3.10/ext4-be-more-strict-when-migrating-to-non-extent-based-file.patch queue-3.10/jbd2-use-gfp_nofs-in-jbd2_cleanup_journal_tail.patch queue-3.10/ext4-replace-open-coded-nofail-allocation-in-ext4_free_blocks.patch queue-3.10/ext4-don-t-retry-file-block-mapping-on-bigalloc-fs-with-non-extent-file.patch queue-3.10/ext4-call-sync_blockdev-before-invalidate_bdev-in-put_super.patch queue-3.10/ext4-fix-race-between-truncate-and-__ext4_journalled_writepage.patch queue-3.10/ext4-fix-reservation-release-on-invalidatepage-for-delalloc-fs.patch