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 DF76B1DF97B; Wed, 6 Nov 2024 02:12:16 +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=1730859137; cv=none; b=roI79DguZzSEaErRDk8x+JTxtCnKqo225hIjiwsnud5cujIIDNN9FVqcQu3RsAlHTvoeI29t/XEGYm9y4YRWqqsC0vzgvRuBT6Dv7295AoejHYlsoah97S9qsmSX/0uFQyx6jtaJnA608OBWAhuuobiRgoYwzU0EnstA4kiU59Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1730859137; c=relaxed/simple; bh=W651HOHjGzMDsCgtNU4gYW/D1n71pQWGsOS7ffSj49I=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=a6br6Fspc+sZS/vUQd0vI/RKM5McOPwK3lr9NcNQDzf6GiNlFwO4IGWMUbRmdc/BfF6gxVRqEH3aie1++2zV3+YBer5eqEgpnjQHE2xfnyWXqZaac4Mfrm7/A37jolFAQmIqDNbYlMfjeN4Y3UiWXMb5asPNqw7yVI0DIg8SscI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=KOkMC0BF; 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="KOkMC0BF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 082B7C4CECF; Wed, 6 Nov 2024 02:12:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1730859136; bh=W651HOHjGzMDsCgtNU4gYW/D1n71pQWGsOS7ffSj49I=; h=From:To:Cc:Subject:Date:From; b=KOkMC0BFa78Sq+EZxLDfcW34TmRYjowgDmeAL0kLIC5zwesvehau0FzOxfRolgeXG decXlwavcVeTmPWsnwnMBzPswFNbkUJ4lCfqQLHAkkcWmgS+cFnC2l54xRV7Ju8VZy 7sj+nEGJe+IqUv+8WgBQ4MFaz9IPpVNyJIydTqB6sULi1xoJOpyU5bapmK+VqBYp65 uRPVMzrCLe3eMtwx1HqS51H21OValeRLSrOAKu038xT9m1bdQVGdHZM9w1PoYSwY2Z L6eEDROrv5tIUCGSHF+zdxEeaIr2PLdzTu6YTHHM38acMj5nAQ1yglGWoyCriDItLx 8xmYHaA2V8Jgw== From: Sasha Levin To: stable@vger.kernel.org, axboe@kernel.dk Cc: Peter Mann , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org Subject: FAILED: Patch "io_uring/rw: fix missing NOWAIT check for O_DIRECT start write" failed to apply to v5.15-stable tree Date: Tue, 5 Nov 2024 21:12:14 -0500 Message-ID: <20241106021214.182779-1-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Hint: ignore X-stable: review Content-Transfer-Encoding: 8bit The patch below does not apply to the v5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From 1d60d74e852647255bd8e76f5a22dc42531e4389 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Thu, 31 Oct 2024 08:05:44 -0600 Subject: [PATCH] io_uring/rw: fix missing NOWAIT check for O_DIRECT start write 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 --- 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 354c4e175654c..155938f100931 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)) -- 2.43.0