linux-kernel - Re: [PATCH] CIFS: silence lockdep splat in cifs_relock

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Message-ID: <CAH2r5muYaCXXhbROUHEe=w1xdzLXFCVASBXv3c20RZgvBU69mw@mail.gmail.com>
Date:   Tue, 9 May 2017 20:38:57 -0500
From:   Steve French <smfrench@...il.com>
To:     Pavel Shilovsky <pshilovsky@...ba.org>
Cc:     Rabin Vincent <rabin.vincent@...s.com>,
        Steve French <sfrench@...ba.org>,
        linux-cifs <linux-cifs@...r.kernel.org>,
        samba-technical <samba-technical@...ts.samba.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jeff Layton <jlayton@...hat.com>,
        Rabin Vincent <rabinv@...s.com>
Subject: Re: [PATCH] CIFS: silence lockdep splat in cifs_relock_file()

merged into cifs-2.6.git for-next

thx

On Tue, May 9, 2017 at 8:34 PM, Pavel Shilovsky <pshilovsky@...ba.org> wrote:
> 2017-05-03 8:17 GMT-07:00 Rabin Vincent <rabin.vincent@...s.com>:
>> From: Rabin Vincent <rabinv@...s.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@...s.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@...rosoft.com>
>
> Best regards,
> Pavel Shilovsky
> --
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-- 
Thanks,

Steve