Re: [PATCH] blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats()

[Tejun Heo <tj@kernel.org>]

On Tue, Jun 06, 2023 at 02:07:24PM -0400, Waiman Long wrote:
> When blkg_alloc() is called to allocate a blkcg_gq structure
> with the associated blkg_iostat_set's, there are 2 fields within
> blkg_iostat_set that requires proper initialization - blkg & sync.
> The former field was introduced by commit 3b8cc6298724 ("blk-cgroup:
> Optimize blkcg_rstat_flush()") while the later one was introduced by
> commit f73316482977 ("blk-cgroup: reimplement basic IO stats using
> cgroup rstat").
> 
> Unfortunately those fields in the blkg_iostat_set's are not properly
> re-initialized when they are cleared in v1's blkcg_reset_stats(). This
> can lead to a kernel panic due to NULL pointer access of the blkg
> pointer. The missing initialization of sync is less problematic and
> can be a problem in a debug kernel due to missing lockdep initialization.
> 
> Fix these problems by re-initializing them after memory clearing.
> 
> Fixes: 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()")
> 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>

Thanks.

-- 
tejun