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 2118244AB62; Tue, 21 Jul 2026 21:49:34 +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=1784670575; cv=none; b=CH6pXOJcq8QOX3LawyFiSuA0cNGPWcBW7y2Owj382ylPorzOu+tHVWK00dyO1Ly+rvysixtw9EPfUKI8dhebDooZGC0pQ8FTPvD00ha7KsLP78lhZeAO2kgHjP0MqXE32GIx3DuCwZ2DL/m8k8hGuJ/EAftl2+gyhmf5ccZsvIY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784670575; c=relaxed/simple; bh=2uH/c8ZcXcvu2KexFWwtP+QYuUwJE50e45WORf74OjM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SPucwcNWvqRPvc9wX1So71XKnq/2lpkbZvAJZRwTiUbd98Q+nlhtSz+5aEkIJnbQo8NaX3anqJSLNDAdU2lRlmD7o48c/MWEeX9VzVm/sP6pbkrh/vTvcpAHo/NsR4JVfaWU5xA7V38LnePzl7RGNVTCenuk6lvYdHk+Epwa+5o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=2EFx0d5S; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="2EFx0d5S" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7B57E1F00A3A; Tue, 21 Jul 2026 21:49:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784670573; bh=KcUvXt0HEnBKN4RncwVBcAoYxOpWH5CsXBQ6ldaJIYE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=2EFx0d5SDSc2d7gTbfXMJ1IBMANRFw3KKcwtzkp8QDluuyyvFw9D7uV12yzLNN/NT ilRhfTOJtASVkybDtJVMQSDKwlBJutVhVxhEiY85hhhkYaljlm1Hwv5WM6xVZVAQ3R bc4w/JPzbrlEP8nnOry/WjJasjnevrK2MIoz5MK0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Shakeel Butt , Zenghui Yu , Nhat Pham , SeongJae Park , Qi Zheng , Muchun Song , Roman Gushchin , Dave Chinner , Andrew Morton , Sasha Levin Subject: [PATCH 6.1 0977/1067] mm/shrinker: do not hold RCU lock in shrinker_debugfs_count_show() Date: Tue, 21 Jul 2026 17:26:18 +0200 Message-ID: <20260721152446.406628669@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260721152424.521567757@linuxfoundation.org> References: <20260721152424.521567757@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Shakeel Butt [ Upstream commit b902890c62d200b3509cb5e09cf1e0a66553c128 ] 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 Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- mm/shrinker_debug.c | 4 ---- 1 file changed, 4 deletions(-) --- a/mm/shrinker_debug.c +++ b/mm/shrinker_debug.c @@ -55,8 +55,6 @@ 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); @@ -86,8 +84,6 @@ 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; }