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[PATCH 3.14 22/29] ext4: fix deadlock during page writeback

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3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@suse.cz>

commit 646caa9c8e196880b41cd3e3d33a2ebc752bdb85 upstream.

Commit 06bd3c36a733 (ext4: fix data exposure after a crash) uncovered a
deadlock in ext4_writepages() which was previously much harder to hit.
After this commit xfstest generic/130 reproduces the deadlock on small
filesystems.

The problem happens when ext4_do_update_inode() sets LARGE_FILE feature
and marks current inode handle as synchronous. That subsequently results
in ext4_journal_stop() called from ext4_writepages() to block waiting for
transaction commit while still holding page locks, reference to io_end,
and some prepared bio in mpd structure each of which can possibly block
transaction commit from completing and thus results in deadlock.

Fix the problem by releasing page locks, io_end reference, and
submitting prepared bio before calling ext4_journal_stop().

[ Changed to defer the call to ext4_journal_stop() only if the handle
  is synchronous.  --tytso ]

Reported-and-tested-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/ext4/inode.c |   29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2579,13 +2579,36 @@ retry:
 				done = true;
 			}
 		}
-		ext4_journal_stop(handle);
+		/*
+		 * Caution: If the handle is synchronous,
+		 * ext4_journal_stop() can wait for transaction commit
+		 * to finish which may depend on writeback of pages to
+		 * complete or on page lock to be released.  In that
+		 * case, we have to wait until after after we have
+		 * submitted all the IO, released page locks we hold,
+		 * and dropped io_end reference (for extent conversion
+		 * to be able to complete) before stopping the handle.
+		 */
+		if (!ext4_handle_valid(handle) || handle->h_sync == 0) {
+			ext4_journal_stop(handle);
+			handle = NULL;
+		}
 		/* Submit prepared bio */
 		ext4_io_submit(&mpd.io_submit);
 		/* Unlock pages we didn't use */
 		mpage_release_unused_pages(&mpd, give_up_on_write);
-		/* Drop our io_end reference we got from init */
-		ext4_put_io_end(mpd.io_submit.io_end);
+		/*
+		 * Drop our io_end reference we got from init. We have
+		 * to be careful and use deferred io_end finishing if
+		 * we are still holding the transaction as we can
+		 * release the last reference to io_end which may end
+		 * up doing unwritten extent conversion.
+		 */
+		if (handle) {
+			ext4_put_io_end_defer(mpd.io_submit.io_end);
+			ext4_journal_stop(handle);
+		} else
+			ext4_put_io_end(mpd.io_submit.io_end);
 
 		if (ret == -ENOSPC && sbi->s_journal) {
 			/*

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[PATCH 3.14 00/29] 3.14.76-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:10 +0200
  [PATCH 3.14 16/29] block: fix use-after-free in seq file Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:10 +0200
  [PATCH 3.14 02/29] mm: migrate dirty page without clear_page_dirty_for_io etc Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:10 +0200
  [PATCH 3.14 10/29] KEYS: 64-bit MIPS needs to use compat_sys_keyctl for 32-bit userspace Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:10 +0200
  [PATCH 3.14 09/29] arm: oabi compat: add missing access checks Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:10 +0200
  [PATCH 3.14 12/29] random: strengthen input validation for RNDADDTOENTCNT Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:10 +0200
  [PATCH 3.14 05/29] sctp: Prevent soft lockup when sctp_accept() is called during a timeout event Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:20 +0200
  [PATCH 3.14 25/29] bonding: set carrier off for devices created through netlink Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:20 +0200
  [PATCH 3.14 01/29] USB: fix invalid memory access in hub_activate() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:20 +0200
  [PATCH 3.14 22/29] ext4: fix deadlock during page writeback Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:20 +0200
  [PATCH 3.14 24/29] ext4: short-cut orphan cleanup on error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:20 +0200
  [PATCH 3.14 28/29] [PATCH 1/8] tcp: make challenge acks less predictable Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:20 +0200
  [PATCH 3.14 11/29] apparmor: fix ref count leak when profile sha1 hash is read Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:20 +0200
  [PATCH 3.14 19/29] crypto: gcm - Filter out async ghash if necessary Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-08-14 22:20 +0200
  Re: [PATCH 3.14 00/29] 3.14.76-stable review Guenter Roeck <linux@roeck-us.net> - 2016-08-15 16:50 +0200
  Re: [PATCH 3.14 00/29] 3.14.76-stable review Shuah Khan <shuah.kh@samsung.com> - 2016-08-16 06:10 +0200

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