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

[nayeem]

On Wednesday 14 September 2016 10:44 AM, Dilger, Andreas wrote:
> On Sep 12, 2016, at 04:27, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxx>
> > > ---
> > > 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

diff --git a/drivers/staging/lustre/lustre/include/lustre_dlm.h b/drivers/staging/lustre/lustre/include/lustre_dlm.h
index 1ec4231..2ae463a 100644
--- a/drivers/staging/lustre/lustre/include/lustre_dlm.h
+++ b/drivers/staging/lustre/lustre/include/lustre_dlm.h
@@ -1293,6 +1293,7 @@ enum lock_res_type {
 
 /** Lock resource. */
 static inline void lock_res(struct ldlm_resource *res)
+			__acquires(&res->lr_lock)
 {
 	spin_lock(&res->lr_lock);
 }
@@ -1306,6 +1307,7 @@ static inline void lock_res_nested(struct ldlm_resource *res,
 
 /** Unlock resource. */
 static inline void unlock_res(struct ldlm_resource *res)
+			__releases(&res->lr_lock)
 {
 	spin_unlock(&res->lr_lock);
 }
diff --git a/drivers/staging/lustre/lustre/ldlm/l_lock.c b/drivers/staging/lustre/lustre/ldlm/l_lock.c
index ea8840c..a887d9f 100644
--- a/drivers/staging/lustre/lustre/ldlm/l_lock.c
+++ b/drivers/staging/lustre/lustre/ldlm/l_lock.c
@@ -45,6 +45,7 @@
  * being an atomic operation.
  */
 struct ldlm_resource *lock_res_and_lock(struct ldlm_lock *lock)
+				__acquires(&lock->l_lock)
 {
 	spin_lock(&lock->l_lock);
 
@@ -59,6 +60,7 @@ EXPORT_SYMBOL(lock_res_and_lock);
  * Unlock a lock and its resource previously locked with lock_res_and_lock
  */
 void unlock_res_and_lock(struct ldlm_lock *lock)
+		__releases(&lock->l_lock)
 {
 	/* on server-side resource of lock doesn't change */
 	ldlm_clear_res_locked(lock);