From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DB18DC433DF for ; Mon, 15 Jun 2020 17:46:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BA5102078A for ; Mon, 15 Jun 2020 17:46:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592243166; bh=U+ToLZUScU7hhZBhe8QFVGjR/yW7bRP2jaPQ3IEQcyQ=; h=From:To:Subject:Date:List-ID:From; b=wY4MPoB1GcJxD22OcIAbkfTn/IC6K0quP13wPzSd1SD2ZvuaI2ju8xYMbB8gffaak ECYMxoaRs7TyRU2jBnd+/js4bunZQPqbgRvCNNYVUFXKtOKFtWwqVZYVERH2MSKHjs 0jF5+GIykzZPJdGmXK0ynqlVD11pcOzw3WodGMvg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731277AbgFORqF (ORCPT ); Mon, 15 Jun 2020 13:46:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:52404 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731270AbgFORqE (ORCPT ); Mon, 15 Jun 2020 13:46:04 -0400 Received: from debian8.Home (bl8-197-74.dsl.telepac.pt [85.241.197.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 15DB32078A for ; Mon, 15 Jun 2020 17:46:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592243164; bh=U+ToLZUScU7hhZBhe8QFVGjR/yW7bRP2jaPQ3IEQcyQ=; h=From:To:Subject:Date:From; b=Iyllm2UFrXofTsZAzMtMqiPSmVEX5KxKDg8zERBmBNZ/A5UMtBBE5jvD8O9mEfAxc i+5K7czzdeGQd0nkKC7i4SZkhSp+CpCRmmIFaYagYzDp5S3YvN6Ri0Q6nEsw75+7N5 k5p95IEYJEnAQGhLZr/OYEesmIHgsY8iF6gZc0B8= From: fdmanana@kernel.org To: linux-btrfs@vger.kernel.org Subject: [PATCH 1/4] Btrfs: fix hang on snapshot creation after RWF_NOWAIT write Date: Mon, 15 Jun 2020 18:46:01 +0100 Message-Id: <20200615174601.14559-1-fdmanana@kernel.org> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org From: Filipe Manana If we do a successful RWF_NOWAIT write we end up locking the snapshot lock of the inode, through a call to check_can_nocow(), but we never unlock it. This means the next attempt to create a snapshot on the subvolume will hang forever. Trivial reproducer: $ mkfs.btrfs -f /dev/sdb $ mount /dev/sdb /mnt $ touch /mnt/foobar $ chattr +C /mnt/foobar $ xfs_io -d -c "pwrite -S 0xab 0 64K" /mnt/foobar $ xfs_io -d -c "pwrite -N -V 1 -S 0xfe 0 64K" /mnt/foobar $ btrfs subvolume snapshot -r /mnt /mnt/snap --> hangs Fix this by unlocking the snapshot lock if check_can_nocow() returned success. Fixes: edf064e7c6fec3 ("btrfs: nowait aio support") CC: stable@vger.kernel.org # 4.13+ Signed-off-by: Filipe Manana --- fs/btrfs/file.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 2c14312b05e8..04faa04fccd1 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -1914,6 +1914,8 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb, inode_unlock(inode); return -EAGAIN; } + /* check_can_nocow() locks the snapshot lock on success */ + btrfs_drew_write_unlock(&root->snapshot_lock); } current->backing_dev_info = inode_to_bdi(inode); -- 2.26.2