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Subject[PATCH 4.4 020/190] CIFS: silence lockdep splat in cifs_relock_file()
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Rabin Vincent <rabinv@axis.com>


[ 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

Signed-off-by: Rabin Vincent <rabinv@axis.com>
Acked-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/cifs/file.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -589,7 +589,7 @@ 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);

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