linux-kernel - Re: [PATCH] staging: lustre: lustre/ldlm: Fixed sparse warnings

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Date:   Fri, 16 Sep 2016 00:03:44 +0530
From:   nayeem <itachi.opsrc@...il.com>
To:     "Dilger, Andreas" <andreas.dilger@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>
CC:     "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Drokin, Oleg" <oleg.drokin@...el.com>,
        James Simmons <jsimmons@...radead.org>,
        Lustre Development List <lustre-devel@...ts.lustre.org>
Subject: Re: [PATCH] staging: lustre: lustre/ldlm: Fixed sparse warnings

On Wednesday 14 September 2016 10:44 AM, Dilger, Andreas wrote:
> On Sep 12, 2016, at 04:27, Greg KH <gregkh@...uxfoundation.org> wrote:
>>
>> On Fri, Sep 09, 2016 at 08:50:35PM +0530, Nayeemahmed Badebade wrote:
>>> Added __acquires / __releases sparse locking annotations
>>> to lock_res_and_lock and unlock_res_and_lock functions in
>>> l_lock.c, to fix below sparse warnings:
>>>
>>> l_lock.c:47:22: warning: context imbalance in 'lock_res_and_lock' - wrong count at exit
>>> l_lock.c:62:6: warning: context imbalance in 'unlock_res_and_lock' - unexpected unlock
>>>
>>> Signed-off-by: Nayeemahmed Badebade <itachi.opsrc@...il.com>
>>> ---
>>> drivers/staging/lustre/lustre/ldlm/l_lock.c | 4 ++++
>>> 1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/staging/lustre/lustre/ldlm/l_lock.c b/drivers/staging/lustre/lustre/ldlm/l_lock.c
>>> index ea8840c..c4b9612 100644
>>> --- a/drivers/staging/lustre/lustre/ldlm/l_lock.c
>>> +++ b/drivers/staging/lustre/lustre/ldlm/l_lock.c
>>> @@ -45,6 +45,8 @@
>>>   * being an atomic operation.
>>>   */
>>> struct ldlm_resource *lock_res_and_lock(struct ldlm_lock *lock)
>>> +				__acquires(&lock->l_lock)
>>> +				__acquires(lock->l_resource)
>>
>> Hm, these are tricky, I don't want to take this type of change without
>> an ack from the lustre developers...
>
> The "__acquires(&lock->l_lock)" line here looks correct, along with the
> corresponding "__releases(&lock->l_lock)" at unlock_res_and_lock().
>
> The problem, however, is that "l_resource" is not a lock, but rather a
> struct.  The call to "lock_res(lock->l_resource)" is actually locking
> "lr_lock" internally.
>
> It would be better to add "__acquires(&res->lr_lock)" at lock_res() and
> "__releases(&res->lr_lock)" at unlock_res().  That will also forestall
> any other warnings about an imbalance with lock_res()/unlock_res() or
> their callsites.
>
> Cheers, Andreas
>

Hi Andreas,

Thank you for your review comments. I did the change according to your 
comments and the diff is attached to mail. But this change doesn't seem 
to fix the sparse warning.
With this change when i compile the code "make C=2 
./drivers/staging/lustre/lustre/", sparse warning still comes:
{{{
   CHECK   drivers/staging/lustre/lustre/ptlrpc/../../lustre/ldlm/l_lock.c
drivers/staging/lustre/lustre/ptlrpc/../../lustre/ldlm/l_lock.c:47:22: 
warning: context imbalance in 'lock_res_and_lock' - wrong count at exit
drivers/staging/lustre/lustre/ptlrpc/../../lustre/ldlm/l_lock.c:62:6: 
warning: context imbalance in 'unlock_res_and_lock' - unexpected unlock
   CC [M]  drivers/staging/lustre/lustre/ptlrpc/../../lustre/ldlm/l_lock.o
}}}

Would it be a good idea to add "__acquires(&lock->l_resource->lr_lock)" 
& "__acquires(&lock->l_lock)" at lock_res_and_lock() and 
"__releases(&lock->l_resource->lr_lock)" & "__releases(&lock->l_lock)" 
at unlock_res_and_lock() ?
Because with that change the sparse warning is fixed.
{{{
   CHECK   drivers/staging/lustre/lustre/ptlrpc/../../lustre/ldlm/l_lock.c
   CC [M]  drivers/staging/lustre/lustre/ptlrpc/../../lustre/ldlm/l_lock.o
}}}
Could you please confirm this.

Regards,
Nayeem

View attachment "sparse-warnings-fix-patch-v2.patch" of type "text/x-patch" (1402 bytes)