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Date: Mon, 02 Aug 2010 14:04:46 +0200
From: Stefan Bader <stefan.bader@...onical.com>
To: Greg KH <gregkh@...e.de>
CC: linux-kernel@...r.kernel.org, stable@...nel.org,
Eric Sandeen <sandeen@...hat.com>, akpm@...ux-foundation.org,
torvalds@...ux-foundation.org, stable-review@...nel.org,
alan@...rguk.ukuu.org.uk
Subject: Re: [Stable-review] [116/165] ext4: dont return to userspace after
freezing the fs with a mutex held
We have reports about this patch breaking lvm snapshhots. Eric, there is a patch
mentioned which is supposed to fix things but its not upstream, yet.
Do you know what happened to that?
-Stefan
PATCH] ext4: fix freeze deadlock under IO
Commit 6b0310fbf087ad6 caused a regression resulting in deadlocks
when freezing a filesystem which had active IO; the vfs_check_frozen
level (SB_FREEZE_WRITE) did not let the freeze-related IO syncing
through. Duh.
Changing the test to FREEZE_TRANS should let the normal freeze
syncing get through the fs, but still block any transactions from
starting once the fs is completely frozen.
I tested this by running fsstress in the background while periodically
snapshotting the fs and running fsck on the result. I ran into
occasional deadlocks, but different ones. I think this is a
fine fix for the problem at hand, and the other deadlocky things
will need more investigation.
Reported-by: Phillip Susi <psusi@....rr.com>
Signed-off-by: Eric Sandeen <sandeen@...hat.com>
---
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 4e8983a..a45ced9 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -241,7 +241,7 @@ handle_t *ext4_journal_start_sb(struct super_block *sb, int
nblocks)
if (sb->s_flags & MS_RDONLY)
return ERR_PTR(-EROFS);
- vfs_check_frozen(sb, SB_FREEZE_WRITE);
+ vfs_check_frozen(sb, SB_FREEZE_TRANS);
/* Special case here: if the journal has aborted behind our
* backs (eg. EIO in the commit thread), then we still need to
* take the FS itself readonly cleanly. */
@@ -3491,7 +3491,7 @@ int ext4_force_commit(struct super_block *sb)
journal = EXT4_SB(sb)->s_journal;
if (journal) {
- vfs_check_frozen(sb, SB_FREEZE_WRITE);
+ vfs_check_frozen(sb, SB_FREEZE_TRANS);
ret = ext4_journal_force_commit(journal);
}
On 07/30/2010 07:15 PM, Greg KH wrote:
> 2.6.32-stable review patch. If anyone has any objections, please let us know.
>
> ------------------
>
> commit 6b0310fbf087ad6e9e3b8392adca97cd77184084 upstream (as of v2.6.34-git13)
>
> ext4_freeze() used jbd2_journal_lock_updates() which takes
> the j_barrier mutex, and then returns to userspace. The
> kernel does not like this:
>
> ================================================
> [ BUG: lock held when returning to user space! ]
> ------------------------------------------------
> lvcreate/1075 is leaving the kernel with locks still held!
> 1 lock held by lvcreate/1075:
> #0: (&journal->j_barrier){+.+...}, at: [<ffffffff811c6214>]
> jbd2_journal_lock_updates+0xe1/0xf0
>
> Use vfs_check_frozen() added to ext4_journal_start_sb() and
> ext4_force_commit() instead.
>
> Addresses-Red-Hat-Bugzilla: #568503
>
> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
> ---
> fs/ext4/super.c | 20 ++++++++++----------
> 1 file changed, 10 insertions(+), 10 deletions(-)
>
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -227,6 +227,7 @@ handle_t *ext4_journal_start_sb(struct s
> if (sb->s_flags & MS_RDONLY)
> return ERR_PTR(-EROFS);
>
> + vfs_check_frozen(sb, SB_FREEZE_WRITE);
> /* Special case here: if the journal has aborted behind our
> * backs (eg. EIO in the commit thread), then we still need to
> * take the FS itself readonly cleanly. */
> @@ -3391,8 +3392,10 @@ int ext4_force_commit(struct super_block
> return 0;
>
> journal = EXT4_SB(sb)->s_journal;
> - if (journal)
> + if (journal) {
> + vfs_check_frozen(sb, SB_FREEZE_WRITE);
> ret = ext4_journal_force_commit(journal);
> + }
>
> return ret;
> }
> @@ -3441,18 +3444,16 @@ static int ext4_freeze(struct super_bloc
> * the journal.
> */
> error = jbd2_journal_flush(journal);
> - if (error < 0) {
> - out:
> - jbd2_journal_unlock_updates(journal);
> - return error;
> - }
> + if (error < 0)
> + goto out;
>
> /* Journal blocked and flushed, clear needs_recovery flag. */
> EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
> error = ext4_commit_super(sb, 1);
> - if (error)
> - goto out;
> - return 0;
> +out:
> + /* we rely on s_frozen to stop further updates */
> + jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
> + return error;
> }
>
> /*
> @@ -3469,7 +3470,6 @@ static int ext4_unfreeze(struct super_bl
> EXT4_SET_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
> ext4_commit_super(sb, 1);
> unlock_super(sb);
> - jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
> return 0;
> }
>
>
>
> _______________________________________________
> Stable-review mailing list
> Stable-review@...ux.kernel.org
> http://linux.kernel.org/mailman/listinfo/stable-review
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