From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753524AbdFQWjx (ORCPT ); Sat, 17 Jun 2017 18:39:53 -0400 Received: from omzsmtpe03.verizonbusiness.com ([199.249.25.208]:14451 "EHLO omzsmtpe03.verizonbusiness.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753181AbdFQWZe (ORCPT ); Sat, 17 Jun 2017 18:25:34 -0400 X-IronPort-Anti-Spam-Filtered: false From: "Levin, Alexander (Sasha Levin)" Cc: Chandan Rajendra , David Sterba , "Levin, Alexander (Sasha Levin)" X-IronPort-AV: E=Sophos;i="5.39,316,1493683200"; d="scan'208";a="372653732" X-Host: viking.odc.vzwcorp.com To: "stable@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: [PATCH for v4.9 LTS 31/86] Btrfs: Fix deadlock between direct IO and fast fsync Thread-Topic: [PATCH for v4.9 LTS 31/86] Btrfs: Fix deadlock between direct IO and fast fsync Thread-Index: AQHS57iB0fhFE5/YokuVIcHPmBZ7yA== Date: Sat, 17 Jun 2017 22:24:38 +0000 Message-ID: <20170617222420.19316-31-alexander.levin@verizon.com> References: <20170617222420.19316-1-alexander.levin@verizon.com> In-Reply-To: <20170617222420.19316-1-alexander.levin@verizon.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-messagesentrepresentingtype: 1 x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.144.60.250] Content-Type: text/plain; charset="iso-8859-1" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id v5HMeBsv023368 From: Chandan Rajendra [ Upstream commit 97dcdea076ecef41ea4aaa23d4397c2f622e4265 ] The following deadlock is seen when executing generic/113 test, ---------------------------------------------------------+---------------------------------------------------- Direct I/O task Fast fsync task ---------------------------------------------------------+---------------------------------------------------- btrfs_direct_IO __blockdev_direct_IO do_blockdev_direct_IO do_direct_IO btrfs_get_blocks_direct while (blocks needs to written) get_more_blocks (first iteration) btrfs_get_blocks_direct btrfs_create_dio_extent down_read(&BTRFS_I(inode) >dio_sem) Create and add extent map and ordered extent up_read(&BTRFS_I(inode) >dio_sem) btrfs_sync_file btrfs_log_dentry_safe btrfs_log_inode_parent btrfs_log_inode btrfs_log_changed_extents down_write(&BTRFS_I(inode) >dio_sem) Collect new extent maps and ordered extents wait for ordered extent completion get_more_blocks (second iteration) btrfs_get_blocks_direct btrfs_create_dio_extent down_read(&BTRFS_I(inode) >dio_sem) -------------------------------------------------------------------------------------------------------------- In the above description, Btrfs direct I/O code path has not yet started submitting bios for file range covered by the initial ordered extent. Meanwhile, The fast fsync task obtains the write semaphore and waits for I/O on the ordered extent to get completed. However, the Direct I/O task is now blocked on obtaining the read semaphore. To resolve the deadlock, this commit modifies the Direct I/O code path to obtain the read semaphore before invoking __blockdev_direct_IO(). The semaphore is then given up after __blockdev_direct_IO() returns. This allows the Direct I/O code to complete I/O on all the ordered extents it creates. Signed-off-by: Chandan Rajendra Reviewed-by: Filipe Manana Signed-off-by: David Sterba Signed-off-by: Sasha Levin --- fs/btrfs/inode.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index bddbae796941..cada3f977baf 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -7235,7 +7235,6 @@ static struct extent_map *btrfs_create_dio_extent(struct inode *inode, struct extent_map *em = NULL; int ret; - down_read(&BTRFS_I(inode)->dio_sem); if (type != BTRFS_ORDERED_NOCOW) { em = create_pinned_em(inode, start, len, orig_start, block_start, block_len, orig_block_len, @@ -7254,7 +7253,6 @@ static struct extent_map *btrfs_create_dio_extent(struct inode *inode, em = ERR_PTR(ret); } out: - up_read(&BTRFS_I(inode)->dio_sem); return em; } @@ -8707,6 +8705,7 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter) dio_data.unsubmitted_oe_range_start = (u64)offset; dio_data.unsubmitted_oe_range_end = (u64)offset; current->journal_info = &dio_data; + down_read(&BTRFS_I(inode)->dio_sem); } else if (test_bit(BTRFS_INODE_READDIO_NEED_LOCK, &BTRFS_I(inode)->runtime_flags)) { inode_dio_end(inode); @@ -8719,6 +8718,7 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb, struct iov_iter *iter) iter, btrfs_get_blocks_direct, NULL, btrfs_submit_direct, flags); if (iov_iter_rw(iter) == WRITE) { + up_read(&BTRFS_I(inode)->dio_sem); current->journal_info = NULL; if (ret < 0 && ret != -EIOCBQUEUED) { if (dio_data.reserve) -- 2.11.0