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    SubjectRe: [PATCH v6 1/3] blk-cgroup: Correctly free percpu iostat_cpu in blkg on error exit
    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@redhat.com>
    > Acked-by: Tejun Heo <tj@kernel.org>
    > ---
    > 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?


    Thanks
    Ming

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