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Koen Kooi
bb34e69f3d
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net> Signed-off-by: Denys Dmytriyenko <denys@ti.com>
120 lines
4.9 KiB
Diff
120 lines
4.9 KiB
Diff
From 4eb9698d0d2e5fb6c0cd910ed3e86154b4d1ea92 Mon Sep 17 00:00:00 2001
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From: Jeff Moyer <jmoyer@redhat.com>
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Date: Mon, 5 Mar 2012 10:29:52 -0500
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Subject: [PATCH 110/147] ext4: fix race between sync and completed io work
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commit 491caa43639abcffaa645fbab372a7ef4ce2975c upstream.
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The following command line will leave the aio-stress process unkillable
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on an ext4 file system (in my case, mounted on /mnt/test):
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aio-stress -t 20 -s 10 -O -S -o 2 -I 1000 /mnt/test/aiostress.3561.4 /mnt/test/aiostress.3561.4.20 /mnt/test/aiostress.3561.4.19 /mnt/test/aiostress.3561.4.18 /mnt/test/aiostress.3561.4.17 /mnt/test/aiostress.3561.4.16 /mnt/test/aiostress.3561.4.15 /mnt/test/aiostress.3561.4.14 /mnt/test/aiostress.3561.4.13 /mnt/test/aiostress.3561.4.12 /mnt/test/aiostress.3561.4.11 /mnt/test/aiostress.3561.4.10 /mnt/test/aiostress.3561.4.9 /mnt/test/aiostress.3561.4.8 /mnt/test/aiostress.3561.4.7 /mnt/test/aiostress.3561.4.6 /mnt/test/aiostress.3561.4.5 /mnt/test/aiostress.3561.4.4 /mnt/test/aiostress.3561.4.3 /mnt/test/aiostress.3561.4.2
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This is using the aio-stress program from the xfstests test suite.
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That particular command line tells aio-stress to do random writes to
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20 files from 20 threads (one thread per file). The files are NOT
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preallocated, so you will get writes to random offsets within the
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file, thus creating holes and extending i_size. It also opens the
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file with O_DIRECT and O_SYNC.
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On to the problem. When an I/O requires unwritten extent conversion,
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it is queued onto the completed_io_list for the ext4 inode. Two code
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paths will pull work items from this list. The first is the
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ext4_end_io_work routine, and the second is ext4_flush_completed_IO,
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which is called via the fsync path (and O_SYNC handling, as well).
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There are two issues I've found in these code paths. First, if the
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fsync path beats the work routine to a particular I/O, the work
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routine will free the io_end structure! It does not take into account
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the fact that the io_end may still be in use by the fsync path. I've
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fixed this issue by adding yet another IO_END flag, indicating that
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the io_end is being processed by the fsync path.
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The second problem is that the work routine will make an assignment to
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io->flag outside of the lock. I have witnessed this result in a hang
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at umount. Moving the flag setting inside the lock resolved that
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problem.
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The problem was introduced by commit b82e384c7b ("ext4: optimize
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locking for end_io extent conversion"), which first appeared in 3.2.
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As such, the fix should be backported to that release (probably along
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with the unwritten extent conversion race fix).
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Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
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Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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fs/ext4/ext4.h | 1 +
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fs/ext4/fsync.c | 2 ++
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fs/ext4/page-io.c | 9 +++++++--
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3 files changed, 10 insertions(+), 2 deletions(-)
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diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
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index 655d942..dbae4d9 100644
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--- a/fs/ext4/ext4.h
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+++ b/fs/ext4/ext4.h
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@@ -185,6 +185,7 @@ struct mpage_da_data {
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#define EXT4_IO_END_ERROR 0x0002
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#define EXT4_IO_END_QUEUED 0x0004
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#define EXT4_IO_END_DIRECT 0x0008
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+#define EXT4_IO_END_IN_FSYNC 0x0010
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struct ext4_io_page {
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struct page *p_page;
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diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
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index 00a2cb7..bb6c7d8 100644
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--- a/fs/ext4/fsync.c
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+++ b/fs/ext4/fsync.c
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@@ -89,6 +89,7 @@ int ext4_flush_completed_IO(struct inode *inode)
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io = list_entry(ei->i_completed_io_list.next,
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ext4_io_end_t, list);
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list_del_init(&io->list);
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+ io->flag |= EXT4_IO_END_IN_FSYNC;
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/*
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* Calling ext4_end_io_nolock() to convert completed
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* IO to written.
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@@ -108,6 +109,7 @@ int ext4_flush_completed_IO(struct inode *inode)
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if (ret < 0)
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ret2 = ret;
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spin_lock_irqsave(&ei->i_completed_io_lock, flags);
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+ io->flag &= ~EXT4_IO_END_IN_FSYNC;
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}
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spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
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return (ret2 < 0) ? ret2 : 0;
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diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
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index 924298a..24feb1c 100644
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--- a/fs/ext4/page-io.c
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+++ b/fs/ext4/page-io.c
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@@ -130,12 +130,18 @@ static void ext4_end_io_work(struct work_struct *work)
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unsigned long flags;
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spin_lock_irqsave(&ei->i_completed_io_lock, flags);
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+ if (io->flag & EXT4_IO_END_IN_FSYNC)
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+ goto requeue;
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if (list_empty(&io->list)) {
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spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
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goto free;
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}
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if (!mutex_trylock(&inode->i_mutex)) {
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+ bool was_queued;
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+requeue:
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+ was_queued = !!(io->flag & EXT4_IO_END_QUEUED);
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+ io->flag |= EXT4_IO_END_QUEUED;
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spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
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/*
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* Requeue the work instead of waiting so that the work
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@@ -148,9 +154,8 @@ static void ext4_end_io_work(struct work_struct *work)
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* yield the cpu if it sees an end_io request that has already
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* been requeued.
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*/
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- if (io->flag & EXT4_IO_END_QUEUED)
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+ if (was_queued)
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yield();
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- io->flag |= EXT4_IO_END_QUEUED;
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return;
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}
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list_del_init(&io->list);
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--
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1.7.9.4
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