From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 68F6527F727; Thu, 5 Feb 2026 13:44:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770299082; cv=none; b=CNJvFqm22gZ6Tj/u2Xnx6xT6nAy4FiA/tlXSGwv+GimmKM1a0Zk4JWFgsftc8DJS8+oZGz8fS0H5urE6kYW9N3WFcnHiGI75hO0nEpsz+NPCiJnJ6G+fT9Qc4xlfJ09HUuY37k3gUlk8AsYWwVR3N+hCQVssynf1NtY+fdIdM1Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770299082; c=relaxed/simple; bh=oN2mtMuaL0wRg06xOfWVYtvkom3Wrc7dRFRV+da+k1M=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=FcM+jHP4mmDeZWzarBeMIeQ0wGAlrzp/xnQp3MM1Ftl+hNl+xjrqOQcLOq3XyGIBaG3CC7VE/x9oerw69/zNced10V2I8Dzn/x3MWyTESeJOhovBAEdebEz8tUgV3oidamQBuxRHEHKLOrjq9IWtjL6L4lWvaK5LluCJLGXO3qo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FLxb9xi7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="FLxb9xi7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A732BC4CEF7; Thu, 5 Feb 2026 13:44:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770299082; bh=oN2mtMuaL0wRg06xOfWVYtvkom3Wrc7dRFRV+da+k1M=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=FLxb9xi7xpxwGHRcQ49oia7/YSMbfNHdByXtrqveYFtcJcf18iTZABv4yGzVX5fZD e6hW7jchgeJzSVFqF1/b43yLZhF/bdXuRezcsdIvlyn13/SBa0XHpkzQswqXMDpX+i YDdqIn6C/yYkOufYz4BJEBJqnWVNLLdZrBoO/XgvShsxNnKcau27tDSQ1n/m/tk4l6 jMFzNGHIN1sc9PmcHB+fsKDHm7ZSVOZx7DX0BHp9dBerqyvX6f2E9G9YCNmyijSNi8 vrKEKmV80Em0+uXpwoTwD9kOU/0Wg4JG7wqhsBxfYO9CzxyBRUdUibDUBpdQIuJIy6 oo7fYTYi+PVAA== Message-ID: <90226c5d-4f0a-4a29-8c5f-1b891e724c2b@kernel.org> Date: Thu, 5 Feb 2026 14:44:37 +0100 Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [BUG] rcu detected stall in shmem_file_write_iter To: Zw Tang , "linux-mm@kvack.org" , rcu@vger.kernel.org Cc: "hughd@google.com" , "akpm@linux-foundation.org" , chrisl@kernel.org, kasong@tencent.com, paulmck@kernel.org, frederic@kernel.org, "linux-kernel@vger.kernel.org" References: From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/5/26 13:57, Zw Tang wrote: > Hi, > > I am reporting a reproducible RCU stall observed on Linux 6.19.0-rc7, > triggered by a syzkaller C reproducer. > > The stall is reported while a userspace task is executing the tmpfs > (shmem) write path. The blocked task is a syz-executor process, and the > RCU report consistently shows it running in the shmem write / folio > allocation path for an extended period of time. > > The relevant call trace of the stalled task is: > > shmem_file_write_iter > shmem_write_begin > shmem_get_folio_gfp > __folio_batch_add_and_move > folio_batch_move_lru > lru_add > __mod_zone_page_state > lru_add()->lruvec_add_folio() calls update_lru_size()->__update_lru_size()->__mod_zone_page_state(). On SMP systems we end up in mm/vmstat.c:__mod_zone_page_state(). I don't see anything that could block in there. Livelocking? Or we're actually stuck somewhere else and the __mod_zone_page_state is misleading. Can you try running with lockdep to see if anything pops up? -- Cheers, David