[PATCH] Fix __wait_on_atomic_t() to call the action func if the counter != 0

[PATCH] Fix __wait_on_atomic_t() to call the action func if the counter != 0

[David Howells]

Fix __wait_on_atomic_t() so that it calls the action func if the counter != 0
rather than if the counter is 0 so as to be analogous to __wait_on_bit().

Thanks to Yacine who found this by visual inspection.

This will affect FS-Cache in that it will could fail to sleep correctly when
trying to clean up after a netfs cookie is withdrawn.

Reported-by: Yacine Belkadi <yacine.belkadi.1@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Yacine Belkadi <yacine.belkadi.1@gmail.com>
cc: Milosz Tanski <milosz@adfin.com>
cc: Jeff Layton <jlayton@redhat.com>
---

 kernel/wait.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/wait.c b/kernel/wait.c
index ce0daa3..dec68bd 100644
--- a/kernel/wait.c
+++ b/kernel/wait.c
@@ -333,7 +333,8 @@ int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
 		prepare_to_wait(wq, &q->wait, mode);
 		val = q->key.flags;
 		if (atomic_read(val) == 0)
-			ret = (*action)(val);
+			break;
+		ret = (*action)(val);
 	} while (!ret && atomic_read(val) != 0);
 	finish_wait(wq, &q->wait);
 	return ret;

Re: [PATCH] Fix __wait_on_atomic_t() to call the action func if the counter != 0

[Jeff Layton]

On Tue, 23 Jul 2013 16:49:24 +0100
David Howells <dhowells@redhat.com> wrote:

> Fix __wait_on_atomic_t() so that it calls the action func if the counter != 0
> rather than if the counter is 0 so as to be analogous to __wait_on_bit().
> 
> Thanks to Yacine who found this by visual inspection.
> 
> This will affect FS-Cache in that it will could fail to sleep correctly when
> trying to clean up after a netfs cookie is withdrawn.
> 
> Reported-by: Yacine Belkadi <yacine.belkadi.1@gmail.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Yacine Belkadi <yacine.belkadi.1@gmail.com>
> cc: Milosz Tanski <milosz@adfin.com>
> cc: Jeff Layton <jlayton@redhat.com>
> ---
> 
>  kernel/wait.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/wait.c b/kernel/wait.c
> index ce0daa3..dec68bd 100644
> --- a/kernel/wait.c
> +++ b/kernel/wait.c
> @@ -333,7 +333,8 @@ int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
>  		prepare_to_wait(wq, &q->wait, mode);
>  		val = q->key.flags;
>  		if (atomic_read(val) == 0)
> -			ret = (*action)(val);
> +			break;
> +		ret = (*action)(val);
>  	} while (!ret && atomic_read(val) != 0);

nit: can you now eliminate the check for "val" in the while condition?
It doesn't look like it harms anything, but eliminating it would
probably simplify the code slightly...

>  	finish_wait(wq, &q->wait);
>  	return ret;
> 
> --
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-- 
Jeff Layton <jlayton@redhat.com>

Re: [PATCH] Fix __wait_on_atomic_t() to call the action func if the counter != 0

[David Howells]

Jeff Layton <jlayton@redhat.com> wrote:

> > @@ -333,7 +333,8 @@ int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
> >  		prepare_to_wait(wq, &q->wait, mode);
> >  		val = q->key.flags;
> >  		if (atomic_read(val) == 0)
> > -			ret = (*action)(val);
> > +			break;
> > +		ret = (*action)(val);
> >  	} while (!ret && atomic_read(val) != 0);
> 
> nit: can you now eliminate the check for "val" in the while condition?
> It doesn't look like it harms anything, but eliminating it would
> probably simplify the code slightly...

Its presence means that we don't have to call prepare_to_wait() again if val
became 0.

David

Re: [PATCH] Fix __wait_on_atomic_t() to call the action func if the counter != 0

[Jeff Layton]

On Tue, 23 Jul 2013 17:15:02 +0100
David Howells <dhowells@redhat.com> wrote:

> Jeff Layton <jlayton@redhat.com> wrote:
> 
> > > @@ -333,7 +333,8 @@ int __wait_on_atomic_t(wait_queue_head_t *wq, struct wait_bit_queue *q,
> > >  		prepare_to_wait(wq, &q->wait, mode);
> > >  		val = q->key.flags;
> > >  		if (atomic_read(val) == 0)
> > > -			ret = (*action)(val);
> > > +			break;
> > > +		ret = (*action)(val);
> > >  	} while (!ret && atomic_read(val) != 0);
> > 
> > nit: can you now eliminate the check for "val" in the while condition?
> > It doesn't look like it harms anything, but eliminating it would
> > probably simplify the code slightly...
> 
> Its presence means that we don't have to call prepare_to_wait() again if val
> became 0.
> 
> David

Ok, and prepare_to_wait involves taking spinlocks, etc...

Got it!

Reviewed-by: Jeff Layton <jlayton@redhat.com>