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 B9377400973; Thu, 16 Jul 2026 14:08:45 +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=1784210926; cv=none; b=VRUlS8rlNUP2YY8Mjz+j+Xz1JJkrBTotVruWUDHreIpFaYsnAc00OyHGoZ2jnKYn1vILgTXpOPK4xbIhNx2kTfO1SVCKDSPeKNm6fVUQ8hXnFdob1wJxaBY46npvbCZEn6hAJD5/zgqUISe/HKXKbz51TvgWqi42jq+5yLBzydE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784210926; c=relaxed/simple; bh=+0MUKvzNn0IutEZkt7l1yR9ZANE+eP4WE/wRcxlo9gM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ElvUIukTPPtkrYqxbiU4BWzbqR7DW61g00EXQ1h7xQz6/HOq2JLwmLSSrv6RyzFW1TBfpWUv8KLVGMM1TP4xwxhHXe/yTJBpw7MXcj0IqfcSmwARw78jhel0Gr/7O2bRldEWjEskGn4O0+CFu0nqqDD8juSPWqsma8JydvK+aCM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=QIN4tbyW; 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="QIN4tbyW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 325281F000E9; Thu, 16 Jul 2026 14:08:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784210925; bh=S3kJA8+8OPfsrlRJnMMkay6w6fcr72fV4U52WrHmfXc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=QIN4tbyWNnJhTbpvvPxERK2KaugdCJVv4zZIGOMuHBsVXN0NEsYMIu1MUeRoH6Ct+ ehhgJ0fbbHLd6691ljzm9IOgCSq8M2v2ciNdCCq02ABnE8fbGUxJf1byZeNaQklHUy annk81GIqieNbd+SLMGfCqX8/vh/mC7A0AkZSzjU= 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 Subject: [PATCH 6.18 189/480] mm/shrinker: do not hold RCU lock in shrinker_debugfs_count_show() Date: Thu, 16 Jul 2026 15:28:56 +0200 Message-ID: <20260716133048.815924698@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260716133044.672218725@linuxfoundation.org> References: <20260716133044.672218725@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 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Shakeel Butt commit b902890c62d200b3509cb5e09cf1e0a66553c128 upstream. 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: Greg Kroah-Hartman --- mm/shrinker_debug.c | 4 ---- 1 file changed, 4 deletions(-) --- a/mm/shrinker_debug.c +++ b/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; }