CVE-2026-64419

In the Linux kernel, the following vulnerability has been resolved:

mm/shrinker: do not hold RCU lock in shrinker_debugfs_count_show()

Reading the debugfs "count" file of a memcg-aware shrinker can sleep

inside an RCU read-side critical section:

BUG: sleeping function called from invalid context at kernel/cgroup/rstat.c:421

RCU nest depth: 1, expected: 0

css_rstat_flush

mem_cgroup_flush_stats

zswap_shrinker_count

shrinker_debugfs_count_show

shrinker_debugfs_count_show() invokes the ->count_objects() callback under

rcu_read_lock(). The zswap callback flushes memcg stats via

css_rstat_flush(), which may sleep, so it must not run under RCU.

The RCU lock is not needed here. mem_cgroup_iter() takes RCU internally

and returns a memcg holding a css reference (dropped on the next iteration

or by mem_cgroup_iter_break()), so the memcg stays alive without it. The

shrinker is kept alive by the open debugfs file: shrinker_free() removes

the debugfs entries via debugfs_remove_recursive(), which waits for

in-flight readers to drain, before call_rcu(..., shrinker_free_rcu_cb).

The sibling "scan" handler already invokes the sleeping ->scan_objects()

callback with no RCU section.

Drop the rcu_read_lock()/rcu_read_unlock().