From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-io1-f42.google.com (mail-io1-f42.google.com [209.85.166.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 20A5419538D for ; Thu, 31 Oct 2024 14:14:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.166.42 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730384081; cv=none; b=dI0jEtOJyVu35gdRy2m7LHPo1PohyDZzgXiX6UO/55oIJsw+HBiHtVXVvOrWJp99ZQSTl30wEepaiYUFbHCv3gg0RS5FXfj2JaXNuWNj3TciiAjr+Gp4hCFxYTg/RWvDbUgkZ4zVOpkItCLyE9Xp9gy8/26kIfUh9VhM/iXdkiM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730384081; c=relaxed/simple; bh=lzQwurv6QT01hIrIbN9ul9GvZ1dQC+rBxi2Lqi7hNl8=; h=Message-ID:Date:MIME-Version:To:From:Subject:Cc:Content-Type; b=ApUXOQ/T4F7jA/J2bk12URb0A3JYLCNSe7Pz8uw61bf0VY8urElI7mmInrk5slSzqyrERBzRrSIjXjERDbqtmZDQr5HrHHzDoOERqPew1xDRc3IAt+v5Yz6pfdqlgap5hidaJzrK8JJacXlOAHEAAaVn6ux29la2EBY0LZn2O0Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.dk; spf=pass smtp.mailfrom=kernel.dk; dkim=pass (2048-bit key) header.d=kernel-dk.20230601.gappssmtp.com header.i=@kernel-dk.20230601.gappssmtp.com header.b=fCnTxz+x; arc=none smtp.client-ip=209.85.166.42 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.dk Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=kernel.dk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20230601.gappssmtp.com header.i=@kernel-dk.20230601.gappssmtp.com header.b="fCnTxz+x" Received: by mail-io1-f42.google.com with SMTP id ca18e2360f4ac-83aad8586d3so37941839f.1 for ; Thu, 31 Oct 2024 07:14:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20230601.gappssmtp.com; s=20230601; t=1730384075; x=1730988875; darn=vger.kernel.org; h=content-transfer-encoding:cc:subject:from:to:content-language :user-agent:mime-version:date:message-id:from:to:cc:subject:date :message-id:reply-to; bh=SHpERe6g4THQHHunVxX4R+p0LPUBUQPPw/vhfS9/TYM=; b=fCnTxz+x8O0XgJTU0V5PkTEA/d/BRi4Yw3wBDRIOAyTD3Xiu6dcflY8816nWFmkJ3f X5GrS9f6wJrh3vquSr5ZksxokVTj7wqp5ICw/2pbwTRj7iSDb7sGJ6ieAeOfFwyZ9Qqc ptJWc9MXwDSoQpkcpXM/SC8oou2sAOfzccpMACUbV2QG+8fiw0tyQTCz39beQ1IxdEKd 21UxNJsKGT7kmUbUDb8lSGjdCwgPjDrZjjg/3DG7LXeOHp8UtILMYi28RRDOC98tP4J5 0g39GgtyZivYSzk9U1Ut/ywcEIn0wwL2ZypzntOcwpm1i5x8gfy6pIyAW2P2M+MDYPxs znsg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1730384075; x=1730988875; h=content-transfer-encoding:cc:subject:from:to:content-language :user-agent:mime-version:date:message-id:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=SHpERe6g4THQHHunVxX4R+p0LPUBUQPPw/vhfS9/TYM=; b=sPwWATUwuwdNiu3+VLPfKWAvke0JGPfK0fEPBjovUbL6ApAf8JbAjActDw00iFOfhX CnrYdE+nq4gOEeEgM2P9jfdFMwatkz0NrU6mwUu65L01zrNqz6SMyxUQYxpIwwrfyIFO MBGt+j4JVuI7lAMtZUM4WMbTzaGoObQJ8pePa2ah0gLDw1l6Ndm7d7YFIVKADP7r3Io4 gYf4GrHkxyZ96siWi8o3EUgTXH4J3R0RbFFTwd2gkhmaGaPjk2nemTy/UYeQDzY1XMoo ORf9Af1RYHur74YS4hkNK+VtvZlsoKLfW4hupk1GhgljEejHwUH8iPNnW5/44bAYMqUi edBQ== X-Gm-Message-State: AOJu0YyU9Ja4yHpr1RzZnoWWua119s9rdYi01dHizX65tgt7mRJNHsZ4 e9oyJxqXjvJOp8leb6IsdbSCPT2jmyzMech064lHK2nFv+9c4DhdnH23pAE6R+/CPjUI70W3lsh viaM= X-Google-Smtp-Source: AGHT+IGo34DKxudFSUmz7+qg4aqR6wHjjmkDImhyVm9Pg6niSXy20hZcUqrRoJdngPZaoXiQrrS7Hw== X-Received: by 2002:a05:6602:29d0:b0:83a:a746:68a6 with SMTP id ca18e2360f4ac-83b1c43e1a0mr2268593139f.5.1730384075328; Thu, 31 Oct 2024 07:14:35 -0700 (PDT) Received: from [192.168.1.116] ([96.43.243.2]) by smtp.gmail.com with ESMTPSA id ca18e2360f4ac-83b67cd0ab8sm33772539f.49.2024.10.31.07.14.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 31 Oct 2024 07:14:34 -0700 (PDT) Message-ID: <46f67f82-846b-4607-902a-c71e3d2a68c6@kernel.dk> Date: Thu, 31 Oct 2024 08:14:34 -0600 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: en-US To: io-uring From: Jens Axboe Subject: [PATCH] io_uring/rw: fix missing NOWAIT check for O_DIRECT start write Cc: Peter Mann Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit When io_uring starts a write, it'll call kiocb_start_write() to bump the super block rwsem, preventing any freezes from happening while that write is in-flight. The freeze side will grab that rwsem for writing, excluding any new writers from happening and waiting for existing writes to finish. But io_uring unconditionally uses kiocb_start_write(), which will block if someone is currently attempting to freeze the mount point. This causes a deadlock where freeze is waiting for previous writes to complete, but the previous writes cannot complete, as the task that is supposed to complete them is blocked waiting on starting a new write. This results in the following stuck trace showing that dependency with the write blocked starting a new write: task:fio state:D stack:0 pid:886 tgid:886 ppid:876 Call trace: __switch_to+0x1d8/0x348 __schedule+0x8e8/0x2248 schedule+0x110/0x3f0 percpu_rwsem_wait+0x1e8/0x3f8 __percpu_down_read+0xe8/0x500 io_write+0xbb8/0xff8 io_issue_sqe+0x10c/0x1020 io_submit_sqes+0x614/0x2110 __arm64_sys_io_uring_enter+0x524/0x1038 invoke_syscall+0x74/0x268 el0_svc_common.constprop.0+0x160/0x238 do_el0_svc+0x44/0x60 el0_svc+0x44/0xb0 el0t_64_sync_handler+0x118/0x128 el0t_64_sync+0x168/0x170 INFO: task fsfreeze:7364 blocked for more than 15 seconds. Not tainted 6.12.0-rc5-00063-g76aaf945701c #7963 with the attempting freezer stuck trying to grab the rwsem: task:fsfreeze state:D stack:0 pid:7364 tgid:7364 ppid:995 Call trace: __switch_to+0x1d8/0x348 __schedule+0x8e8/0x2248 schedule+0x110/0x3f0 percpu_down_write+0x2b0/0x680 freeze_super+0x248/0x8a8 do_vfs_ioctl+0x149c/0x1b18 __arm64_sys_ioctl+0xd0/0x1a0 invoke_syscall+0x74/0x268 el0_svc_common.constprop.0+0x160/0x238 do_el0_svc+0x44/0x60 el0_svc+0x44/0xb0 el0t_64_sync_handler+0x118/0x128 el0t_64_sync+0x168/0x170 Fix this by having the io_uring side honor IOCB_NOWAIT, and only attempt a blocking grab of the super block rwsem if it isn't set. For normal issue where IOCB_NOWAIT would always be set, this returns -EAGAIN which will have io_uring core issue a blocking attempt of the write. That will in turn also get completions run, ensuring forward progress. Cc: stable@vger.kernel.org # 5.10+ Reported-by: Peter Mann Link: https://lore.kernel.org/io-uring/38c94aec-81c9-4f62-b44e-1d87f5597644@sh.cz Signed-off-by: Jens Axboe --- diff --git a/io_uring/rw.c b/io_uring/rw.c index 354c4e175654..155938f10093 100644 --- a/io_uring/rw.c +++ b/io_uring/rw.c @@ -1014,6 +1014,25 @@ int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags) return IOU_OK; } +static bool io_kiocb_start_write(struct io_kiocb *req, struct kiocb *kiocb) +{ + struct inode *inode; + bool ret; + + if (!(req->flags & REQ_F_ISREG)) + return true; + if (!(kiocb->ki_flags & IOCB_NOWAIT)) { + kiocb_start_write(kiocb); + return true; + } + + inode = file_inode(kiocb->ki_filp); + ret = sb_start_write_trylock(inode->i_sb); + if (ret) + __sb_writers_release(inode->i_sb, SB_FREEZE_WRITE); + return ret; +} + int io_write(struct io_kiocb *req, unsigned int issue_flags) { bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK; @@ -1051,8 +1070,8 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags) if (unlikely(ret)) return ret; - if (req->flags & REQ_F_ISREG) - kiocb_start_write(kiocb); + if (unlikely(!io_kiocb_start_write(req, kiocb))) + return -EAGAIN; kiocb->ki_flags |= IOCB_WRITE; if (likely(req->file->f_op->write_iter)) -- Jens Axboe