Re: [PATCH v6 1/3] blk-cgroup: Correctly free percpu iostat_cpu in blkg on error exit

[Waiman Long]

On 6/3/22 22:08, Ming Lei wrote:
> On Thu, Jun 02, 2022 at 03:20:18PM -0400, Waiman Long wrote:
> > Commit f73316482977 ("blk-cgroup: reimplement basic IO stats using cgroup
> > rstat") changes block cgroup IO stats to use the rstat APIs. It added
> > a new percpu iostat_cpu field into blkg. The blkg_alloc() was modified
> > to allocate the new percpu iostat_cpu but didn't free it when an error
> > happened. Fix this by freeing the percpu iostat_cpu on error exit.
> >
> > Fixes: f73316482977 ("blk-cgroup: reimplement basic IO stats using cgroup rstat")
> > Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> > Acked-by: Tejun Heo <tj@xxxxxxxxxx>
> > ---
> >   block/blk-cgroup.c | 7 +++++--
> >   1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> > index 40161a3f68d0..acd9b0aa8dc8 100644
> > --- a/block/blk-cgroup.c
> > +++ b/block/blk-cgroup.c
> > @@ -219,11 +219,11 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
> >   		return NULL;
> >   
> >   	if (percpu_ref_init(&blkg->refcnt, blkg_release, 0, gfp_mask))
> > -		goto err_free;
> > +		goto err_free_blkg;
> >   
> >   	blkg->iostat_cpu = alloc_percpu_gfp(struct blkg_iostat_set, gfp_mask);
> >   	if (!blkg->iostat_cpu)
> > -		goto err_free;
> > +		goto err_free_blkg;
> >   
> >   	if (!blk_get_queue(q))
> >   		goto err_free;
> > @@ -259,6 +259,9 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
> >   	return blkg;
> >   
> >   err_free:
> > +	free_percpu(blkg->iostat_cpu);
> > +
> > +err_free_blkg:
> >   	blkg_free(blkg);
> Hi Waiman,
>
> But blkg_free() frees blkg->iostat_cpu via blkg_free_workfn(), so I am
> confused where the leak is in failure path?

Yes, you are right. I have overlooked that. So this patch isn't really 
necessary. Thanks for correcting me.

Cheers,
Longman