Miao Xie
2012-Mar-22 03:13 UTC
[RFC PATCH 2/2] Btrfs: fix deadlock on umount by umount_prepare interface
The reason the deadlock is that:
Task Btrfs-cleaner
umount()
down_write(&s->s_umount)
close_ctree()
wait for the end of
btrfs-cleaner
start_transaction
reserve space
shrink_delalloc()
writeback_inodes_sb_nr_if_idle()
down_read(&sb->s_umount)
So, the deadlock has happened.
The safest way to fix this problem is to close the btrfs-cleaner before
the umount is ready to continue. Since we have introduced umount_prepare
interface into vfs before, we can fix this problem by it.
Reported-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
---
fs/btrfs/disk-io.c | 15 ---------------
fs/btrfs/super.c | 22 ++++++++++++++++++++++
2 files changed, 22 insertions(+), 15 deletions(-)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 534266f..34ebd6e 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -3017,21 +3017,6 @@ int close_ctree(struct btrfs_root *root)
struct btrfs_fs_info *fs_info = root->fs_info;
int ret;
- fs_info->closing = 1;
- smp_mb();
-
- /* pause restriper - we want to resume on mount */
- btrfs_pause_balance(root->fs_info);
-
- btrfs_scrub_cancel(root);
-
- /* wait for any defraggers to finish */
- wait_event(fs_info->transaction_wait,
- (atomic_read(&fs_info->defrag_running) == 0));
-
- /* clear out the rbtree of defraggable inodes */
- btrfs_run_defrag_inodes(fs_info);
-
/*
* Here come 2 situations when btrfs is broken to flip readonly:
*
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 3ce97b2..24ed903 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -145,6 +145,27 @@ void __btrfs_std_error(struct btrfs_fs_info *fs_info, const
char *function,
btrfs_handle_error(fs_info);
}
+static void btrfs_umount_prepare(struct super_block *sb)
+{
+ struct btrfs_root *root = btrfs_sb(sb)->tree_root;
+ struct btrfs_fs_info *fs_info = root->fs_info;
+
+ fs_info->closing = 1;
+ smp_mb();
+
+ /* pause restriper - we want to resume on mount */
+ btrfs_pause_balance(root->fs_info);
+
+ btrfs_scrub_cancel(root);
+
+ /* wait for any defraggers to finish */
+ wait_event(fs_info->transaction_wait,
+ (atomic_read(&fs_info->defrag_running) == 0));
+
+ /* clear out the rbtree of defraggable inodes */
+ btrfs_run_defrag_inodes(fs_info);
+}
+
static void btrfs_put_super(struct super_block *sb)
{
(void)close_ctree(btrfs_sb(sb)->tree_root);
@@ -1312,6 +1333,7 @@ static void btrfs_fs_dirty_inode(struct inode *inode, int
flags)
static const struct super_operations btrfs_super_ops = {
.drop_inode = btrfs_drop_inode,
.evict_inode = btrfs_evict_inode,
+ .umount_prepare = btrfs_umount_prepare,
.put_super = btrfs_put_super,
.sync_fs = btrfs_sync_fs,
.show_options = btrfs_show_options,
--
1.7.6.5
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Dave Chinner
2012-Mar-22 04:39 UTC
Re: [RFC PATCH 2/2] Btrfs: fix deadlock on umount by umount_prepare interface
On Thu, Mar 22, 2012 at 11:13:17AM +0800, Miao Xie wrote:> The reason the deadlock is that: > Task Btrfs-cleaner > umount() > down_write(&s->s_umount) > close_ctree() > wait for the end of > btrfs-cleaner > start_transaction > reserve space > shrink_delalloc() > writeback_inodes_sb_nr_if_idle() > down_read(&sb->s_umount) > So, the deadlock has happened.Every time a deadlock involving writeback_inodes_sb...if_idle() comes up, I give the same response. If the s_umount is write locked, then the sb is not idle. IOWs, writeback_inodes_sb...if_idle() should be doing down_read_trylock(), not down_read(). Cheers, Dave. -- Dave Chinner david@fromorbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Miao Xie
2012-Mar-22 05:25 UTC
Re: [RFC PATCH 2/2] Btrfs: fix deadlock on umount by umount_prepare interface
On Thu, 22 Mar 2012 15:39:36 +1100, Dave Chinner wrote:> On Thu, Mar 22, 2012 at 11:13:17AM +0800, Miao Xie wrote: >> The reason the deadlock is that: >> Task Btrfs-cleaner >> umount() >> down_write(&s->s_umount) >> close_ctree() >> wait for the end of >> btrfs-cleaner >> start_transaction >> reserve space >> shrink_delalloc() >> writeback_inodes_sb_nr_if_idle() >> down_read(&sb->s_umount) >> So, the deadlock has happened. > > Every time a deadlock involving writeback_inodes_sb...if_idle() > comes up, I give the same response. If the s_umount is write locked, > then the sb is not idle. IOWs, writeback_inodes_sb...if_idle() > should be doing down_read_trylock(), not down_read().Someone did this work several months ago, but those patches have not been applied until now, so... https://lkml.org/lkml/2011/12/8/264 Thanks Miao -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Dave Chinner
2012-Mar-22 06:29 UTC
Re: [RFC PATCH 2/2] Btrfs: fix deadlock on umount by umount_prepare interface
On Thu, Mar 22, 2012 at 01:25:26PM +0800, Miao Xie wrote:> On Thu, 22 Mar 2012 15:39:36 +1100, Dave Chinner wrote: > > On Thu, Mar 22, 2012 at 11:13:17AM +0800, Miao Xie wrote: > >> The reason the deadlock is that: > >> Task Btrfs-cleaner > >> umount() > >> down_write(&s->s_umount) > >> close_ctree() > >> wait for the end of > >> btrfs-cleaner > >> start_transaction > >> reserve space > >> shrink_delalloc() > >> writeback_inodes_sb_nr_if_idle() > >> down_read(&sb->s_umount) > >> So, the deadlock has happened. > > > > Every time a deadlock involving writeback_inodes_sb...if_idle() > > comes up, I give the same response. If the s_umount is write locked, > > then the sb is not idle. IOWs, writeback_inodes_sb...if_idle() > > should be doing down_read_trylock(), not down_read(). > > Someone did this work several months ago, but those patches have not been > applied until now, so...... work to get them into the current/next release. Cheers, Dave. -- Dave Chinner david@fromorbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html