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From: Qi Zheng In-Reply-To: <20260610232048.62930-1-shakeel.butt@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 5FE1E18000B X-Rspam-User: X-Stat-Signature: kjf765mmuaasz69arop4pihjroa4ocms X-Rspamd-Server: rspam09 X-HE-Tag: 1781148653-430821 X-HE-Meta: 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 26b2bWOJ wM+63NPYhVmuDBf/gV7nbVF5T+EXb6aMCslIqWaGL+d/1NQMm5kAzzu3sjgpwprtj9bR7/nbKdAkuPduMOanmylkNYqd+rBZdT9LwvelO3AFIVw9QaaprZC/n8T7JMLfZ+WhyeEh807QWQELVUkDKoAK0/GJoeiQqRO3soEPiWaAQLgoygXUEGyQ77SSz2dq+1wh5WRgBgfz++5K+kGXrMy1xPpxu+X8R5DJtxpIVsW++LJ0o5HnPkSIWteYlGAdE/KpGsV6In6vo2nP2MFignKk2VvNDXRdR/ykYr8dSZPdHLbc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/11/26 7:20 AM, Shakeel Butt wrote: > 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(). > > Fixes: 5035ebc644ae ("mm: shrinkers: introduce debugfs interface for memory shrinkers") > Reported-by: Zenghui Yu > Closes: https://lore.kernel.org/all/c052a064-cddb-494f-a0d8-f8a10b4b1c4d@linux.dev/ > Suggested-by: Nhat Pham > Signed-off-by: Shakeel Butt > --- > mm/shrinker_debug.c | 4 ---- > 1 file changed, 4 deletions(-) > LGTM, so: Reviewed-by: Qi Zheng Thanks!