From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-178.mta0.migadu.com (out-178.mta0.migadu.com [91.218.175.178]) (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 2C43335898 for ; Sun, 26 Apr 2026 15:58:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777219089; cv=none; b=aadeuwQGUTv2jTQq4fac300ll5pGrSD5Tkb7/GbUV8ZmJEDJVGsHHtgLBcWlh18cBQp8WsZfz9hxhU0AC+jRHizNuaoyToE4zhA8PFRWQc6Ptg1u7h3w3R3ZxAzfMQvBmS3tZNEebgi06WUNyTEtd1zivdM18P1Oprfd7YhWvnk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777219089; c=relaxed/simple; bh=LliZn59Ks38xfDPQ3rXvfu+6hjM8F9PxxFsd0w502/w=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Dz+R/CnpvSOX8D4X7UgdfQeXmmfR52STx3h0xfN9UpFymmQERqccv8N8QRAkDQKTfWviNz6GfKI0KfFeYjTgvSk/zptyeyDdrc7CTTUDZPq7fB9br49uME/ErkzSwplDtffhle9FXQVu+SxgpNdMh6iKI4jZ7GZ/d/KKZZe/1Qg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=YkviZMLb; arc=none smtp.client-ip=91.218.175.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="YkviZMLb" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1777219085; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=4F6gB/xx6VdA5bb9zTaCkR+ngYQ60IUg/PkZ8TsJ+TM=; b=YkviZMLbpQYaBN4JXqzO6Mdl1Ofdh94oik7QKN6ZWiWGSp+wJ1bysFJSq9yhwtyv4trYg3 ALCtLJykxXf13/wWsTKyd3QQa5UvDRhVOJtSIQfZ6Y0Tc9oG2dWl6Ow2AQJoBDgifaHmUd t4bTDETusCI3JuxGQGprT54gSw5Jnis= Date: Sun, 26 Apr 2026 23:57:42 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [syzbot] [mm?] WARNING: bad unlock balance in do_wp_page To: Andrew Morton , shakeel.butt@linux.dev, syzbot Cc: Liam.Howlett@oracle.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, surenb@google.com, syzkaller-bugs@googlegroups.com, vbabka@kernel.org, Muchun Song References: <69edca15.170a0220.38e3f1.0000.GAE@google.com> <20260426034938.db29d74982a8eb8463f8cf3a@linux-foundation.org> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: <20260426034938.db29d74982a8eb8463f8cf3a@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT Hi Andrew, On 4/26/26 6:49 PM, Andrew Morton wrote: > On Sun, 26 Apr 2026 01:17:25 -0700 syzbot wrote: > >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: 6596a02b2078 Merge tag 'drm-next-2026-04-22' of https://gi.. >> git tree: upstream >> console output: https://syzkaller.appspot.com/x/log.txt?x=12483702580000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=24c8da4692f901cb >> dashboard link: https://syzkaller.appspot.com/bug?extid=7d60b33a8a546263da7c >> compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44 >> userspace arch: i386 >> >> Unfortunately, I don't have any reproducer for this issue yet. > > argh, that dreaded sentence. > > Thanks. > > Something's definitely amiss. This is at least the fifth report of > rcu_read_lock() imbalance post-7.0. Others: > > https://lore.kernel.org/69eab803.a00a0220.17a17.004a.GAE@google.com > https://lore.kernel.org/69eab803.a00a0220.17a17.004b.GAE@google.com > https://lore.kernel.org/69eafb0e.a00a0220.9259.0031.GAE@google.com > https://lore.kernel.org/69ebcbe2.a00a0220.7773.0005.GAE@google.com All the kernel configs mentioned above include 'CONFIG_MEMCG_V1=y'. Theoretically, a rebind_subsystems() can lead a rcu unbalance, see my previous discussion with Shakeel for details: https://lore.kernel.org/all/358c60e1-fa91-40a1-9e00-84c93340c04e@linux.dev/ However, in a production environment, this is practically impossible. So Shakeel and I chose to wait for a reproducer at the time. :( > > In some cases we released it too often, in other cases we failed to > release it. > > The first one is slightly more useful in that it tells us that the > not-released rcu_read_lock() was taken in folio_lruvec_lock_irqsave(). I double-checked some callers of folio_lruvec_lock_irqsave() (such as folios_put_refs()), but didn't find anything suspicious. :( > > Muchun & Qi: you played with that rcu locking in 31b54a5e8916. Can you > please double-check that we didn't miss something?