Patch "reiserfs: Unlock superblock before calling reiserfs_quota_on_mount()" has been added to the 4.7-stable tree

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

reiserfs: Unlock superblock before calling reiserfs_quota_on_mount()

to the 4.7-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:
reiserfs-unlock-superblock-before-calling-reiserfs_quota_on_mount.patch
and it can be found in the queue-4.7 subdirectory.

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

From: Mike Galbraith <[email protected]>
Date: Mon, 13 Aug 2012 15:21:23 +0200
Subject: reiserfs: Unlock superblock before calling reiserfs_quota_on_mount()

From: Mike Galbraith <[email protected]>

commit 420902c9d086848a7548c83e0a49021514bd71b7 upstream.

If we hold the superblock lock while calling reiserfs_quota_on_mount(), we can deadlock our own worker - mount blocks kworker/3:2, sleeps forever more.

crash> ps|grep UN

    715      2   3  ffff880220734d30  UN   0.0       0      0  [kworker/3:2]
   9369   9341   2  ffff88021ffb7560  UN   1.3  493404 123184  Xorg
   9665   9664   3  ffff880225b92ab0  UN   0.0   47368    812  udisks-daemon
  10635  10403   3  ffff880222f22c70  UN   0.0   14904    936  mount

crash> bt ffff880220734d30
PID: 715 TASK: ffff880220734d30 CPU: 3 COMMAND: "kworker/3:2"
#0 [ffff8802244c3c20] schedule at ffffffff8144584b
#1 [ffff8802244c3cc8] __rt_mutex_slowlock at ffffffff814472b3 #2 [ffff8802244c3d28] rt_mutex_slowlock at ffffffff814473f5 #3 [ffff8802244c3dc8] reiserfs_write_lock at ffffffffa05f28fd [reiserfs] #4 [ffff8802244c3de8] flush_async_commits at ffffffffa05ec91d [reiserfs] #5 [ffff8802244c3e08] process_one_work at ffffffff81073726 #6 [ffff8802244c3e68] worker_thread at ffffffff81073eba
#7 [ffff8802244c3ec8] kthread at ffffffff810782e0
#8 [ffff8802244c3f48] kernel_thread_helper at ffffffff81450064
crash> rd ffff8802244c3cc8 10

ffff8802244c3cc8:  ffffffff814472b3 ffff880222f23250   .rD.....P2."....
ffff8802244c3cd8:  0000000000000000 0000000000000286   ................
ffff8802244c3ce8:  ffff8802244c3d30 ffff880220734d80   0=L$.....Ms ....
ffff8802244c3cf8:  ffff880222e8f628 0000000000000000   (.."............
ffff8802244c3d08:  0000000000000000 0000000000000002   ................
crash> struct rt_mutex ffff880222e8f628
struct rt_mutex {
  wait_lock = {
    raw_lock = {
      slock = 65537
    }
  },
  wait_list = {
    node_list = {
      next = 0xffff8802244c3d48,
      prev = 0xffff8802244c3d48
    }

},
owner = 0xffff880222f22c71,
save_state = 0
}
crash> bt 0xffff880222f22c70
PID: 10635 TASK: ffff880222f22c70 CPU: 3 COMMAND: "mount"
#0 [ffff8802216a9868] schedule at ffffffff8144584b
#1 [ffff8802216a9910] schedule_timeout at ffffffff81446865 #2 [ffff8802216a99a0] wait_for_common at ffffffff81445f74
#3 [ffff8802216a9a30] flush_work at ffffffff810712d3
#4 [ffff8802216a9ab0] schedule_on_each_cpu at ffffffff81074463 #5 [ffff8802216a9ae0] invalidate_bdev at ffffffff81178aba
#6 [ffff8802216a9af0] vfs_load_quota_inode at ffffffff811a3632 #7 [ffff8802216a9b50] dquot_quota_on_mount at ffffffff811a375c #8 [ffff8802216a9b80] finish_unfinished at ffffffffa05dd8b0 [reiserfs] #9 [ffff8802216a9cc0] reiserfs_fill_super at ffffffffa05de825 [reiserfs]

    RIP: 00007f7b9303997a  RSP: 00007ffff443c7a8  RFLAGS: 00010202
    RAX: 00000000000000a5  RBX: ffffffff8144ef12  RCX: 00007f7b932e9ee0
    RDX: 00007f7b93d9a400  RSI: 00007f7b93d9a3e0  RDI: 00007f7b93d9a3c0
    RBP: 00007f7b93d9a2c0   R8: 00007f7b93d9a550   R9: 0000000000000001
    R10: ffffffffc0ed040e  R11: 0000000000000202  R12: 000000000000040e
    R13: 0000000000000000  R14: 00000000c0ed040e  R15: 00007ffff443ca20
    ORIG_RAX: 00000000000000a5  CS: 0033  SS: 002b

---
 fs/reiserfs/super.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

@@ -190,7 +190,15 @@ static int remove_save_link_only(struct
 static int reiserfs_quota_on_mount(struct super_block *, int);
 #endif
 
-/* look for uncompleted unlinks and truncates and complete them */
+/*
+ * Look for uncompleted unlinks and truncates and complete them
+ *
+ * Called with superblock write locked.  If quotas are enabled, we have to
+ * release/retake lest we call dquot_quota_on_mount(), proceed to
+ * schedule_on_each_cpu() in invalidate_bdev() and deadlock waiting for the per
+ * cpu worklets to complete flush_async_commits() that in turn wait for the
+ * superblock write lock.
+ */
 static int finish_unfinished(struct super_block *s)
 {
 	INITIALIZE_PATH(path);

@@ -237,7 +245,9 @@ static int finish_unfinished(struct supe
 				quota_enabled[i] = 0;
 				continue;
 			}
+			reiserfs_write_unlock(s);
 			ret = reiserfs_quota_on_mount(s, i);
+			reiserfs_write_lock(s);
 			if (ret < 0)
 				reiserfs_warning(s, "reiserfs-2500",
 						 "cannot turn on journaled "

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

queue-4.7/reiserfs-unlock-superblock-before-calling-reiserfs_quota_on_mount.patch