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 F39A5185924; Fri, 15 Nov 2024 06:56:55 +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=1731653816; cv=none; b=uC8CFRMCnTm91U9YqID8xT0NWpk1w5eVoVhRuxDpxfPMuorodI9HwFUpM/bWHCQyAKNZ5GoYRZE6dZZS9O1g4BWws2PLYQg0KXnIzGxfCiveQ3d+uR1DzpqS/64Ymx3r4d3NErhJEnZFH6FbzhcomceZfEiNe5cIioPQ7yoNYxY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731653816; c=relaxed/simple; bh=mSpIRO81547JWc5qohTwwtwLGOTwGylDqEqC8KiIHSw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=r24h19C0hl99On3lYoH1JIAc2mlPp2GSAd9FPG8UgF7Et+Y7hh6aL5v848xTWu0L2kX6QOzsi4KKh0l8ojWEYzBUYQHx7PA58js3TqWdOwMOXbqFN/c3vVDZdLiwyGFrz4SEqSW6EYjDtJjRTqWXG4MA2Gt/rt2DF43j1BXcSvg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=dsLJHgvg; 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="dsLJHgvg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 71A10C4CECF; Fri, 15 Nov 2024 06:56:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1731653815; bh=mSpIRO81547JWc5qohTwwtwLGOTwGylDqEqC8KiIHSw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dsLJHgvgj+/mmRVfL13DmdJqQ392FHmQQ1JFo1qg0vkNyBAjoCdLqmgHbDTNShctz vOrSkTiJdh+FcOG/MZ9QW7o5IavFIErTFwdfOGqiIHSC92ZuXQ8HJKRu5t8Hduua/m KIsIIBkL0GGqpFA8UKkun3Sl3rREbbekAbigz9ss= 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 5.10 44/82] io_uring/rw: fix missing NOWAIT check for O_DIRECT start write Date: Fri, 15 Nov 2024 07:38:21 +0100 Message-ID: <20241115063727.146110254@linuxfoundation.org> X-Mailer: git-send-email 2.47.0 In-Reply-To: <20241115063725.561151311@linuxfoundation.org> References: <20241115063725.561151311@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 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jens Axboe Commit 1d60d74e852647255bd8e76f5a22dc42531e4389 upstream. 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/io_uring.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index a6afdea5cfd8e..57c51e9638753 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -3719,6 +3719,25 @@ static int io_write_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) return io_prep_rw(req, sqe, WRITE); } +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; +} + static int io_write(struct io_kiocb *req, unsigned int issue_flags) { struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs; @@ -3765,8 +3784,8 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags) if (unlikely(ret)) goto out_free; - if (req->flags & REQ_F_ISREG) - kiocb_start_write(kiocb); + if (unlikely(!io_kiocb_start_write(req, kiocb))) + goto copy_iov; kiocb->ki_flags |= IOCB_WRITE; if (req->file->f_op->write_iter) -- 2.43.0