From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BCAE5370ADF; Sun, 21 Jun 2026 18:40:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782067215; cv=none; b=jnbsR11D7I9Wp+3QxJtYmCjRDOCDUCc/zhWouPpoKxU6gh02DGVqtfd3jLSC8GhODZyRabUOODq8xZT9Mea2mpkp2SaToEYkZuf70HZwQ0IvXD5PUfEnkW+F4X/v+z4V2KzPDzXntrtWs9E/dVptIBEHNzT73oX62+2/nJPwas8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782067215; c=relaxed/simple; bh=IEgGdovKG21OV1fSQ2QTQm07EyaUK+ccec7eDASXCE4=; h=Date:To:From:Subject:Message-Id; b=J6ooSeXloHqunqwzYomQ9sHi2wboxLlCKRT0EkWiDN2AzyqxClqetbxD4KWmU9o7HUe9P1UpTdfTQKi61f48bkq8pnTv4p8XyiBnLX/bMZhuAEjXiVg5cg/xPotTEvNSIiy40HVVFapTVpkHrTY9MNr+kmGKjmhK1qVLQlsT0KA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=QOXdGh2v; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="QOXdGh2v" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 91B151F000E9; Sun, 21 Jun 2026 18:40:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1782067214; bh=nWNLucxAyNs/BZ5OD5atVidWYyrarN7q8s8k0BiGrpI=; h=Date:To:From:Subject; b=QOXdGh2vxk1bnn4b9YOUtT5PrTnO1aNfPP2jXgt8TlGaNqikXTSQroGLt8V4SSFth q1aP+vHNaT9zSCUMUN1U9tCBp6maPmg2a//s+87ZC8fbV8FLNBro1sbDtHtMY5qRIi r9E00iM+8UxnhjA6X8GR4qBmR3Z1mi44iz6HE7no= Date: Sun, 21 Jun 2026 11:40:14 -0700 To: mm-commits@vger.kernel.org,zenghui.yu@linux.dev,stable@vger.kernel.org,sj@kernel.org,roman.gushchin@linux.dev,qi.zheng@linux.dev,nphamcs@gmail.com,muchun.song@linux.dev,david@fromorbit.com,shakeel.butt@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-stable] mm-shrinker-do-not-hold-rcu-lock-in-shrinker_debugfs_count_show.patch removed from -mm tree Message-Id: <20260621184014.91B151F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm/shrinker: do not hold RCU lock in shrinker_debugfs_count_show() has been removed from the -mm tree. Its filename was mm-shrinker-do-not-hold-rcu-lock-in-shrinker_debugfs_count_show.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Shakeel Butt Subject: mm/shrinker: do not hold RCU lock in shrinker_debugfs_count_show() Date: Wed, 10 Jun 2026 16:20:48 -0700 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(). Link: https://lore.kernel.org/20260610232048.62930-1-shakeel.butt@linux.dev Fixes: 5035ebc644ae ("mm: shrinkers: introduce debugfs interface for memory shrinkers") Signed-off-by: Shakeel Butt Reported-by: Zenghui Yu Closes: https://lore.kernel.org/all/c052a064-cddb-494f-a0d8-f8a10b4b1c4d@linux.dev/ Suggested-by: Nhat Pham Reviewed-by: SeongJae Park Reviewed-by: Qi Zheng Tested-by: Zenghui Yu (Huawei) Reviewed-by: Nhat Pham Acked-by: Muchun Song Reviewed-by: Roman Gushchin Cc: Dave Chinner Cc: Signed-off-by: Andrew Morton --- mm/shrinker_debug.c | 4 ---- 1 file changed, 4 deletions(-) --- a/mm/shrinker_debug.c~mm-shrinker-do-not-hold-rcu-lock-in-shrinker_debugfs_count_show +++ a/mm/shrinker_debug.c @@ -57,8 +57,6 @@ static int shrinker_debugfs_count_show(s if (!count_per_node) return -ENOMEM; - rcu_read_lock(); - memcg_aware = shrinker->flags & SHRINKER_MEMCG_AWARE; memcg = mem_cgroup_iter(NULL, NULL, NULL); @@ -88,8 +86,6 @@ static int shrinker_debugfs_count_show(s } } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL); - rcu_read_unlock(); - kfree(count_per_node); return ret; } _ Patches currently in -mm which might be from shakeel.butt@linux.dev are