On Tue, Jul 27, 2021 at 01:04:49PM -1000, Tejun Heo wrote:

0fa294fb1985 ("cgroup: Replace cgroup_rstat_mutex with a spinlock") added
cgroup_rstat_flush_irqsafe() allowing flushing to happen from the irq
context. However, rstat paths use u64_stats_sync to synchronize access to
64bit stat counters on 32bit machines. u64_stats_sync is implemented using
seq_lock and trying to read from an irq context can lead to A-A deadlock if
the irq happens to interrupt the stat update.

Fix it by using the irqsafe variants - u64_stats_update_begin_irqsave() and
u64_stats_update_end_irqrestore() - in the update paths. Note that none of
this matters on 64bit machines. All these are just for 32bit SMP setups.

Signed-off-by: Tejun Heo <redacted>
Reported-by: Rik van Riel <redacted>

Applying this to cgroup/for-5.14-fixes with stable tag added.

Thanks.

-- 
tejun