From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:50752 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751112AbdFEOJQ (ORCPT ); Mon, 5 Jun 2017 10:09:16 -0400 Subject: Patch "xfs: use ->b_state to fix buffer I/O accounting release race" has been added to the 4.9-stable tree To: bfoster@redhat.com, darrick.wong@oracle.com, gregkh@linuxfoundation.org, lpechacek@suse.com, nborisov@suse.com Cc: , From: Date: Mon, 05 Jun 2017 16:09:05 +0200 Message-ID: <1496671745207117@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled xfs: use ->b_state to fix buffer I/O accounting release race to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: xfs-use-b_state-to-fix-buffer-i-o-accounting-release-race.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 63db7c815bc0997c29e484d2409684fdd9fcd93b Mon Sep 17 00:00:00 2001 From: Brian Foster Date: Wed, 31 May 2017 08:22:52 -0700 Subject: xfs: use ->b_state to fix buffer I/O accounting release race From: Brian Foster commit 63db7c815bc0997c29e484d2409684fdd9fcd93b upstream. We've had user reports of unmount hangs in xfs_wait_buftarg() that analysis shows is due to btp->bt_io_count == -1. bt_io_count represents the count of in-flight asynchronous buffers and thus should always be >= 0. xfs_wait_buftarg() waits for this value to stabilize to zero in order to ensure that all untracked (with respect to the lru) buffers have completed I/O processing before unmount proceeds to tear down in-core data structures. The value of -1 implies an I/O accounting decrement race. Indeed, the fact that xfs_buf_ioacct_dec() is called from xfs_buf_rele() (where the buffer lock is no longer held) means that bp->b_flags can be updated from an unsafe context. While a user-level reproducer is currently not available, some intrusive hacks to run racing buffer lookups/ioacct/releases from multiple threads was used to successfully manufacture this problem. Existing callers do not expect to acquire the buffer lock from xfs_buf_rele(). Therefore, we can not safely update ->b_flags from this context. It turns out that we already have separate buffer state bits and associated serialization for dealing with buffer LRU state in the form of ->b_state and ->b_lock. Therefore, replace the _XBF_IN_FLIGHT flag with a ->b_state variant, update the I/O accounting wrappers appropriately and make sure they are used with the correct locking. This ensures that buffer in-flight state can be modified at buffer release time without racing with modifications from a buffer lock holder. Fixes: 9c7504aa72b6 ("xfs: track and serialize in-flight async buffers against unmount") Signed-off-by: Brian Foster Reviewed-by: Nikolay Borisov Tested-by: Libor Pechacek Reviewed-by: Darrick J. Wong Signed-off-by: Darrick J. Wong Signed-off-by: Greg Kroah-Hartman --- fs/xfs/xfs_buf.c | 38 ++++++++++++++++++++++++++------------ fs/xfs/xfs_buf.h | 5 ++--- 2 files changed, 28 insertions(+), 15 deletions(-) --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -96,12 +96,16 @@ static inline void xfs_buf_ioacct_inc( struct xfs_buf *bp) { - if (bp->b_flags & (XBF_NO_IOACCT|_XBF_IN_FLIGHT)) + if (bp->b_flags & XBF_NO_IOACCT) return; ASSERT(bp->b_flags & XBF_ASYNC); - bp->b_flags |= _XBF_IN_FLIGHT; - percpu_counter_inc(&bp->b_target->bt_io_count); + spin_lock(&bp->b_lock); + if (!(bp->b_state & XFS_BSTATE_IN_FLIGHT)) { + bp->b_state |= XFS_BSTATE_IN_FLIGHT; + percpu_counter_inc(&bp->b_target->bt_io_count); + } + spin_unlock(&bp->b_lock); } /* @@ -109,14 +113,24 @@ xfs_buf_ioacct_inc( * freed and unaccount from the buftarg. */ static inline void -xfs_buf_ioacct_dec( +__xfs_buf_ioacct_dec( struct xfs_buf *bp) { - if (!(bp->b_flags & _XBF_IN_FLIGHT)) - return; + ASSERT(spin_is_locked(&bp->b_lock)); - bp->b_flags &= ~_XBF_IN_FLIGHT; - percpu_counter_dec(&bp->b_target->bt_io_count); + if (bp->b_state & XFS_BSTATE_IN_FLIGHT) { + bp->b_state &= ~XFS_BSTATE_IN_FLIGHT; + percpu_counter_dec(&bp->b_target->bt_io_count); + } +} + +static inline void +xfs_buf_ioacct_dec( + struct xfs_buf *bp) +{ + spin_lock(&bp->b_lock); + __xfs_buf_ioacct_dec(bp); + spin_unlock(&bp->b_lock); } /* @@ -148,9 +162,9 @@ xfs_buf_stale( * unaccounted (released to LRU) before that occurs. Drop in-flight * status now to preserve accounting consistency. */ - xfs_buf_ioacct_dec(bp); - spin_lock(&bp->b_lock); + __xfs_buf_ioacct_dec(bp); + atomic_set(&bp->b_lru_ref, 0); if (!(bp->b_state & XFS_BSTATE_DISPOSE) && (list_lru_del(&bp->b_target->bt_lru, &bp->b_lru))) @@ -953,12 +967,12 @@ xfs_buf_rele( * ensures the decrement occurs only once per-buf. */ if ((atomic_read(&bp->b_hold) == 1) && !list_empty(&bp->b_lru)) - xfs_buf_ioacct_dec(bp); + __xfs_buf_ioacct_dec(bp); goto out_unlock; } /* the last reference has been dropped ... */ - xfs_buf_ioacct_dec(bp); + __xfs_buf_ioacct_dec(bp); if (!(bp->b_flags & XBF_STALE) && atomic_read(&bp->b_lru_ref)) { /* * If the buffer is added to the LRU take a new reference to the --- a/fs/xfs/xfs_buf.h +++ b/fs/xfs/xfs_buf.h @@ -63,7 +63,6 @@ typedef enum { #define _XBF_KMEM (1 << 21)/* backed by heap memory */ #define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */ #define _XBF_COMPOUND (1 << 23)/* compound buffer */ -#define _XBF_IN_FLIGHT (1 << 25) /* I/O in flight, for accounting purposes */ typedef unsigned int xfs_buf_flags_t; @@ -83,14 +82,14 @@ typedef unsigned int xfs_buf_flags_t; { _XBF_PAGES, "PAGES" }, \ { _XBF_KMEM, "KMEM" }, \ { _XBF_DELWRI_Q, "DELWRI_Q" }, \ - { _XBF_COMPOUND, "COMPOUND" }, \ - { _XBF_IN_FLIGHT, "IN_FLIGHT" } + { _XBF_COMPOUND, "COMPOUND" } /* * Internal state flags. */ #define XFS_BSTATE_DISPOSE (1 << 0) /* buffer being discarded */ +#define XFS_BSTATE_IN_FLIGHT (1 << 1) /* I/O in flight */ /* * The xfs_buftarg contains 2 notions of "sector size" - Patches currently in stable-queue which might be from bfoster@redhat.com are queue-4.9/xfs-fix-missed-holes-in-seek_hole-implementation.patch queue-4.9/xfs-use-dedicated-log-worker-wq-to-avoid-deadlock-with-cil-wq.patch queue-4.9/xfs-rework-the-inline-directory-verifiers.patch queue-4.9/xfs-use-b_state-to-fix-buffer-i-o-accounting-release-race.patch queue-4.9/xfs-verify-inline-directory-data-forks.patch