DEBUG_RWSEMS warning from thaw_super()

Commit Message

Oleg Nesterov May 13, 2018, 4:04 p.m. UTC

On 05/13, Amir Goldstein wrote:
>
> Since kernel v4.17-rc1 and DEBUG_RWSEMS, I see the
> warning below after filesystem freeze/thaw.
>
> This is a case where one process acquires a bunch of rwsem
> and another process releases them.
>
> To convey this use case to lockdep, freeze_super() calls
> lockdep_sb_freeze_release() on exit and thaw_super()
> calls lockdep_sb_freeze_acquire() on entry.

This was already discussed, but I forgot the result...

So once again, why we can't simply update percpu_rwsem_acquire() ?
Or we can check CONFIG_RWSEM_SPIN_ON_OWNER to match percpu_rwsem_release(),
but CONFIG_DEBUG_RWSEMS explains the purpose better.

Oleg.

Comments

Jan Kara May 14, 2018, 9:50 a.m. UTC | #1

On Sun 13-05-18 18:04:04, Oleg Nesterov wrote:
> On 05/13, Amir Goldstein wrote:
> >
> > Since kernel v4.17-rc1 and DEBUG_RWSEMS, I see the
> > warning below after filesystem freeze/thaw.
> >
> > This is a case where one process acquires a bunch of rwsem
> > and another process releases them.
> >
> > To convey this use case to lockdep, freeze_super() calls
> > lockdep_sb_freeze_release() on exit and thaw_super()
> > calls lockdep_sb_freeze_acquire() on entry.
> 
> This was already discussed, but I forgot the result...
> 
> So once again, why we can't simply update percpu_rwsem_acquire() ?
> Or we can check CONFIG_RWSEM_SPIN_ON_OWNER to match percpu_rwsem_release(),
> but CONFIG_DEBUG_RWSEMS explains the purpose better.

Yeah, what you suggests seems reasonable to me. So feel free to add:

Acked-by: Jan Kara <[e-mail]>
	
								Honza

> --- x/include/linux/percpu-rwsem.h
> +++ x/include/linux/percpu-rwsem.h
> @@ -141,6 +141,10 @@ static inline void percpu_rwsem_acquire(
>  					bool read, unsigned long ip)
>  {
>  	lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
> +#ifdef CONFIG_DEBUG_RWSEMS
> +	if (!read)
> +		sem->rw_sem.owner = current;
> +#endif
>  }
>  
>  #endif
>

Patch

--- x/include/linux/percpu-rwsem.h
+++ x/include/linux/percpu-rwsem.h
@@ -141,6 +141,10 @@  static inline void percpu_rwsem_acquire(
 					bool read, unsigned long ip)
 {
 	lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
+#ifdef CONFIG_DEBUG_RWSEMS
+	if (!read)
+		sem->rw_sem.owner = current;
+#endif
 }
 
 #endif