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SubjectRe: [PATCH] CIFS: silence lockdep splat in cifs_relock_file()
2017-05-03 8:17 GMT-07:00 Rabin Vincent <rabin.vincent@axis.com>:
> From: Rabin Vincent <rabinv@axis.com>
>
> 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>
> ---
> fs/cifs/file.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 21d4045..64b590b 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -582,7 +582,7 @@ cifs_relock_file(struct cifsFileInfo *cfile)
> 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);
> --
> 2.1.4
>
> --
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Acked-by: Pavel Shilovsky <pshilov@microsoft.com>

Best regards,
Pavel Shilovsky

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