Patch "CIFS: silence lockdep splat in cifs_relock_file()" has been added to the 3.18-stable tree

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

CIFS: silence lockdep splat in cifs_relock_file()

to the 3.18-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:
cifs-silence-lockdep-splat-in-cifs_relock_file.patch
and it can be found in the queue-3.18 subdirectory.

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

From: Rabin Vincent <[email protected]>
Date: Wed, 3 May 2017 17:17:21 +0200
Subject: CIFS: silence lockdep splat in cifs_relock_file()

From: Rabin Vincent <[email protected]>

[ Upstream commit 560d388950ceda5e7c7cdef7f3d9a8ff297bbf9d ]

cifs_relock_file() can perform a down_write() on the inode's lock_sem even though it was already performed in cifs_strict_readv(). Lockdep complains about this. AFAICS, there is no problem here, and lockdep just needs to be told that this nesting is OK.

=============================================
[ INFO: possible recursive locking detected ] 4.11.0+ #20 Not tainted
---------------------------------------------
cat/701 is trying to acquire lock:
(&cifsi->lock_sem){++++.+}, at: cifs_reopen_file+0x7a7/0xc00

but task is already holding lock:
(&cifsi->lock_sem){++++.+}, at: cifs_strict_readv+0x177/0x310

other info that might help us debug this:

  Possible unsafe locking scenario:

        CPU0
        ----

lock(&cifsi->lock_sem);
lock(&cifsi->lock_sem);

*** DEADLOCK ***

May be due to missing lock nesting notation

1 lock held by cat/701:
#0: (&cifsi->lock_sem){++++.+}, at: cifs_strict_readv+0x177/0x310

 stack backtrace:
 CPU: 0 PID: 701 Comm: cat Not tainted 4.11.0+ #20
 Call Trace:
  dump_stack+0x85/0xc2
  __lock_acquire+0x17dd/0x2260
  ? trace_hardirqs_on_thunk+0x1a/0x1c
  ? preempt_schedule_irq+0x6b/0x80
  lock_acquire+0xcc/0x260
  ? lock_acquire+0xcc/0x260
  ? cifs_reopen_file+0x7a7/0xc00
  down_read+0x2d/0x70
  ? cifs_reopen_file+0x7a7/0xc00
  cifs_reopen_file+0x7a7/0xc00
  ? printk+0x43/0x4b
  cifs_readpage_worker+0x327/0x8a0
  cifs_readpage+0x8c/0x2a0
  generic_file_read_iter+0x692/0xd00
  cifs_strict_readv+0x29f/0x310
  generic_file_splice_read+0x11c/0x1c0
  do_splice_to+0xa5/0xc0
  splice_direct_to_actor+0xfa/0x350
  ? generic_pipe_buf_nosteal+0x10/0x10
  do_splice_direct+0xb5/0xe0
  do_sendfile+0x278/0x3a0
  SyS_sendfile64+0xc4/0xe0
  entry_SYSCALL_64_fastpath+0x1f/0xbe

---
 fs/cifs/file.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -583,7 +583,7 @@ cifs_relock_file(struct cifsFileInfo *cf
 	struct cifs_tcon *tcon = tlink_tcon(cfile->tlink);
 	int rc = 0;
 
-	down_read(&cinode->lock_sem);
+	down_read_nested(&cinode->lock_sem, SINGLE_DEPTH_NESTING);
 	if (cinode->can_cache_brlcks) {
 		/* can cache locks - no need to relock */
 		up_read(&cinode->lock_sem);

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

queue-3.18/cifs-silence-lockdep-splat-in-cifs_relock_file.patch