From: Waiman Long longman@redhat.com
[ Upstream commit 3d2af77e31ade05ff7ccc3658c3635ec1bea0979 ]
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 Reviewed-by: Ming Lei ming.lei@redhat.com Acked-by: Tejun Heo tj@kernel.org Link: https://lore.kernel.org/r/20230606180724.2455066-1-longman@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- block/blk-cgroup.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index ad0cd992a6519..c50da8b3af029 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -585,8 +585,13 @@ static int blkcg_reset_stats(struct cgroup_subsys_state *css, struct blkg_iostat_set *bis = per_cpu_ptr(blkg->iostat_cpu, cpu); memset(bis, 0, sizeof(*bis)); + + /* Re-initialize the cleared blkg_iostat_set */ + u64_stats_init(&bis->sync); + bis->blkg = blkg; } memset(&blkg->iostat, 0, sizeof(blkg->iostat)); + u64_stats_init(&blkg->iostat.sync);
for (i = 0; i < BLKCG_MAX_POLS; i++) { struct blkcg_policy *pol = blkcg_policy[i];