Patch "blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats()" has been added to the 6.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats()

to the 6.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     blk-cgroup-reinit-blkg_iostat_set-after-clearing-in-.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 82689b7bb25bd2b9aab7f1c15825afca13cf107f
Author: Waiman Long <longman@xxxxxxxxxx>
Date:   Tue Jun 6 14:07:24 2023 -0400

    blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats()
    
    [ 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@xxxxxxxxxx>
    Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
    Acked-by: Tejun Heo <tj@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230606180724.2455066-1-longman@xxxxxxxxxx
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 5215bc7af5514..aaf9903ad7b2f 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -624,8 +624,13 @@ 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];