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 D6D2228DF34; Tue, 10 Jun 2025 11:09:42 +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=1749553782; cv=none; b=a9fzPS6XkZD/6vL89PplYmhl9oks+swiSACsvqW8rXsE6pCcWgDU2wdP8cpPv/j2YNpKsoX+k6uhmdD3wv/cE1uAKeDx/VeQ6Zj3p855l8eRj06vlDxTLrwo+gCCPN1h0Jr1BNuCnueNRiI/kaX/zF48c/jfyT8Br4ag6s8B3K0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749553782; c=relaxed/simple; bh=tgyH2Rx7rWrKVsHxuyQmZZSHD4p6E22uAdONWEt6Li4=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=jXqBeaA2u/L+pH8zt6vozWJoHfzpUyDtCDyEQDJyJQG4vFEkd+Rc6oB418Z4DTBp6tnTimG1SqZ/cBUTwlKfH7+aNtNXMLonPTyN9vAdrOnfJ54YVh4yxZ4IFob42RIdH7MW70O3O3KP2nzs52lDIYuEvmRop+1PGna9m8CcVkk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=aKhfh38o; 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="aKhfh38o" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C313FC4CEED; Tue, 10 Jun 2025 11:09:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1749553782; bh=tgyH2Rx7rWrKVsHxuyQmZZSHD4p6E22uAdONWEt6Li4=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=aKhfh38oQd97iKW2PyfcNkxUVqC1XbpqpBGggaZn4tJl7Vgq9FABd/Wtm6YORDG7m q3A7Ktoqh83RvCgCI0IHau3A/xW/pExU0FtRlLSBOYtNVxJonwMxSrGu51qJ7Um1HO 0tKz1PjY2QLOcOIvaOnxWmCmtkfFzbxN/51XZn+utdF3K5Q45zxdEuGidQGCl5ARO4 VK+d+zT3ZQ7saiKvs2N1f93dS9k1GwNmN2Vl2nYCtOAjejBYKTFVOWaA4rpPKCHouy 7H9Uq8V6zQbcE1Lj/ICu8S3pq0e01pV4QWsJ8/Hjl4Z7WiSeO/ugZCnveY5LRd7X2a r6cHadTHB8Msg== Message-ID: <208bd615061231c035a5633b29190925f271bd4b.camel@kernel.org> Subject: Re: [PATCH v2 1/5] nfsd: prevent callback tasks running concurrently From: Jeff Layton To: ChenXiaoSong Cc: Olga Kornievskaia , Li Lingfeng , Dai Ngo , Neil Brown , Chuck Lever , Tom Talpey , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Date: Tue, 10 Jun 2025 07:09:40 -0400 In-Reply-To: <23651194C61FBB9C+e2ddd3f5-f51f-44c0-8800-d2abb08a2447@chenxiaosong.com> References: <20250220-nfsd-callback-v2-0-6a57f46e1c3a@kernel.org> <20250220-nfsd-callback-v2-1-6a57f46e1c3a@kernel.org> <23651194C61FBB9C+e2ddd3f5-f51f-44c0-8800-d2abb08a2447@chenxiaosong.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw 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Evolution 3.56.2 (3.56.2-1.fc42) Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Tue, 2025-06-10 at 16:49 +0800, ChenXiaoSong wrote: > =E5=9C=A8 2025/2/21 00:47, Jeff Layton =E5=86=99=E9=81=93: > > Most of the nfsd4_run_cb() callers are converted to use this new flag o= r > > the nfsd4_try_run_cb() wrapper. The main exception is the callback > > channel probe, which has its own synchronization. > >=20 >=20 > Hi Jeff: >=20 > We had a null-ptr-deref in nfsd4_probe_callback(): >=20 > [24225.738349] Unable to handle kernel NULL pointer dereference at=20 > virtual address 0000000000000000 > ... > [24225.803480] Call trace: > [24225.804639] __queue_work+0xb4/0x558 > [24225.805949] queue_work_on+0x88/0x90 > [24225.807306] nfsd4_probe_callback+0x4c/0x58 [nfsd] > [24225.808896] nfsd4_probe_callback_sync+0x20/0x38 [nfsd] > [24225.808909] nfsd4_init_conn.isra.57+0x8c/0xa8 [nfsd] > [24225.815204] nfsd4_create_session+0x5b8/0x718 [nfsd] > [24225.817711] nfsd4_proc_compound+0x4c0/0x710 [nfsd] > [24225.819329] nfsd_dispatch+0x104/0x248 [nfsd] > [24225.820742] svc_process_common+0x348/0x808 [sunrpc] > [24225.822294] svc_process+0xb0/0xc8 [sunrpc] > [24225.823760] nfsd+0xf0/0x160 [nfsd] > [24225.825006] kthread+0x134/0x138 > [24225.826336] ret_from_fork+0x10/0x18 >=20 > Is this patch or patchset can fix this issue? And I'm having trouble=20 > understanding the commit message "callback channel probe has its own=20 > synchronization", I'd appreciate it if you could explain in more detail. >=20 Synchronization was probably too strong a word. I remember looking over this code and convincing myself that the probe callback wasn't subject to the same races as the others, but I think that was mostly because the outcome of those races was not harmful. Note that the probe itself can actually be run at the start of a completely unrelated callback to the same client. So you hit a NULL pointer in __queue_work()? The work_struct is embedded in the nfs4_client so that would probably imply that that the nfs4_client struct was corrupt? You may want to get a vmcore and analyze it if you can reproduce this. --=20 Jeff Layton