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[PATCH] CIFS: silence lockdep splat in cifs_relock_file()

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  [PATCH] CIFS: silence lockdep splat in cifs_relock_file() Rabin Vincent <rabin.vincent@axis.com> - 2017-05-03 17:20 +0200
    Re: [PATCH] CIFS: silence lockdep splat in cifs_relock_file() Steve French <smfrench@gmail.com> - 2017-05-10 03:40 +0200
    Re: [PATCH] CIFS: silence lockdep splat in cifs_relock_file() Pavel Shilovsky <pshilovsky@samba.org> - 2017-05-10 03:40 +0200

#1635070 — [PATCH] CIFS: silence lockdep splat in cifs_relock_file()

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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#1638486

merged into cifs-2.6.git for-next

thx

On Tue, May 9, 2017 at 8:34 PM, Pavel Shilovsky <pshilovsky@samba.org> wrote:
> 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
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-cifs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
> Acked-by: Pavel Shilovsky <pshilov@microsoft.com>
>
> Best regards,
> Pavel Shilovsky
> --
> To unsubscribe from this list: send the line "unsubscribe linux-cifs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html



-- 
Thanks,

Steve

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#1638487

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
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-cifs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Acked-by: Pavel Shilovsky <pshilov@microsoft.com>

Best regards,
Pavel Shilovsky

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