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 E6F0F1FB883; Wed, 6 Nov 2024 12:54:44 +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=1730897685; cv=none; b=IVSESM2Y8V8EkjJ+5gEMQK3A+bnjWgG7NzqYXRW3KWxgzd4uttMOPLagSaCibFAqkpmyWRYeiWKFnsRM6adhVcOisOvgq8McYrhlrnL79o9c7st0mBECrEEshBLXLa/w4HNPei3j/OM3eUWdxcDMRnDW6nuP3MkIGjdy+umzXZM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730897685; c=relaxed/simple; bh=YjNjddJDYBVJ2J75LflDE0bJJxrCmmh1HdaeAoYFVW8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=cLsnjCk/s1CkYPUOUCcAtkam+NYqNr2HHw8TU0GtCz+Yn1BlkXkuIqXpr6WIU/xFpvTfh7LlLMY5pz5pUO/lNQ7S6aQs3VpjtLWBzQLxJVz2xKpkzqlPH+Qun+6glzrOKxHQFakCL+eQ1UvXnYTefBYAl5fbFk7zT/hfsGTXp4I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=VYRlR3ho; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="VYRlR3ho" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6EE7CC4CECD; Wed, 6 Nov 2024 12:54:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1730897684; bh=YjNjddJDYBVJ2J75LflDE0bJJxrCmmh1HdaeAoYFVW8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VYRlR3hog7j5ivnqOeKLnZJAOf8Cd6Zme+NF41YA2d9FWCmoOsDJa9VS2cordO3i1 2i7RUkKIGwPkRtAOiBlO8Kv0bqJgP6eOj3QXBOV+P6n4pKB9ujPyax5LBzdGzjSBTO ZX6uMWKFysCcQnz00hpeiTEBqRCin7mr3Chnhc6c= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Peter Mann , Jens Axboe , Sasha Levin Subject: [PATCH 6.6 136/151] io_uring/rw: fix missing NOWAIT check for O_DIRECT start write Date: Wed, 6 Nov 2024 13:05:24 +0100 Message-ID: <20241106120312.598770549@linuxfoundation.org> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20241106120308.841299741@linuxfoundation.org> References: <20241106120308.841299741@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jens Axboe [ Upstream commit 1d60d74e852647255bd8e76f5a22dc42531e4389 ] 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. Since freezing requires CAP_SYS_ADMIN in the first place, this isn't something that can be triggered by a regular user. 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 Signed-off-by: Sasha Levin --- io_uring/rw.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/io_uring/rw.c b/io_uring/rw.c index 0a0c1c9db0f90..e90404c812fa2 100644 --- a/io_uring/rw.c +++ b/io_uring/rw.c @@ -860,6 +860,25 @@ int io_read(struct io_kiocb *req, unsigned int issue_flags) return kiocb_done(req, ret, issue_flags); } +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) { struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw); @@ -913,8 +932,8 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags) 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)) -- 2.43.0