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>
---
block/blk-cgroup.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 90c2efc3767f..48084321e3e0 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -636,8 +636,13 @@ 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];
--
2.31.1
