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 5A3553B3899 for ; Tue, 25 Aug 2026 06:12:18 +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=1787638339; cv=none; b=XsEtRdFDuYQNaheWAfFr4S0bJSVi8Zno2nEhOPvU6IGawzJQrUpaMRRNAKdD5k8MSvgbbWsdBCds9aUhnZnzW8BnelYMuDTIGY5HjGOSw+JHBjOtuzsQbMKF299K7Z9yF871M0/uCV4yiCKPhZu1dS95bOKWhbiGHnQpWdk7xzk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787638339; c=relaxed/simple; bh=8mNetr/+3wPybXK6X1dkM5oO+P0Dsq3ZEgYaYQ3AHo0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=XhaeZbi2gEKnkQ/sx0E8gBgEOTkGS6uQvHP0Wtaq6/5epB8NyQY93x2U8WCBOUBKKrZMxznvfy7Kwx2jVmx9Uc2ABxGCybkaoxBQA9B6Fs6CUEIRH7cF3jZ11/NgKiVLZ9sUqit6Pf6clxaSY1da5DB8XCTaZ12+p6lJE66cCsQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HAZBHk89; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="HAZBHk89" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 87EB91F00A3A; Tue, 25 Aug 2026 06:12:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787638338; bh=QLkYwJhSrppDaC75EDNyyo/yPnnKezeIKJ2EQPyFq8E=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=HAZBHk89ukFLiZ7HwDBBYlp7iwmWcm5nDfb7ev9uvLuc90LOR5Gyk53GtB4XRWU8U Ud/KyhMuqHQlCAJgsE3nfZI0xPVniyBLc8x/lwnL4ewGL1crxzfAWJpLRtKUNVw4el qTaOflJ2XJToZPwuh4yhyAS5JRAvw1pFPWMvlSm0oUzfTC1CAgi0JaarWWpTT9b1wF A8udn3pTnvX0rx7waalmFnBH9EyeJfGiH4bmpkaWcmDqm3zaEA4zw5AvR0nAAYzsyj 7RiaSpdEIaIM6V9PNT1VHaaXJZVouUXY8Je0cY2ZUWdHWNm5Y2A7b/hG4sjH4QIgbD jQvXPCsOErgMA== Message-ID: <041af2b5-9136-4027-b35a-72e5044c63ab@kernel.org> Date: Tue, 25 Aug 2026 08:12:09 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/shrinker: do not hold RCU lock in shrinker_debugfs_count_show() To: Nick Huang , Shakeel Butt Cc: Andrew Morton , Dave Chinner , Roman Gushchin , Muchun Song , Qi Zheng , Meta kernel team , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Zenghui Yu , Nhat Pham References: <20260610232048.62930-1-shakeel.butt@linux.dev> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 24/08/2026 15:42, Nick Huang wrote: > On Wed, Jun 10, 2026 at 04:20:48PM -0700, 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(-) >> >> diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c >> index affa64437302..cda4e86428c8 100644 >> --- a/mm/shrinker_debug.c >> +++ b/mm/shrinker_debug.c >> @@ -57,8 +57,6 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v) >> 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(struct seq_file *m, void *v) >> } >> } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL); >> >> - rcu_read_unlock(); >> - >> kfree(count_per_node); >> return ret; >> } >> -- >> 2.53.0-Meta >> > Reviewed-by: Nick Huang Sorry, but what exactly did you review here? In the past you were sending AI slop: https://lore.kernel.org/all/aeNGbNyPxJssnkbO@lucifer/ Not even properly following the process. https://lore.kernel.org/all/20260724143408.175870-1-sef1548@gmail.com/ https://lore.kernel.org/all/?q=f%3Asef1548%40gmail.com Why suddenly reviewing MM patches? Best regards, Krzysztof