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From: Stefan Bader on 2 Aug 2010 08:10
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(a)cfl.rr.com>
Signed-off-by: Eric Sandeen <sandeen(a)redhat.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(a)redhat.com>
> Signed-off-by: "Theodore Ts'o" <tytso(a)mit.edu>
> Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.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(a)linux.kernel.org
> http://linux.kernel.org/mailman/listinfo/stable-review

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From: Eric Sandeen on 2 Aug 2010 13:10
On 08/02/2010 07:04 AM, Stefan Bader wrote:
> 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?

right, patch below is needed to fix things.

Ted just acked it on the list recently; Greg, I'd either drop 116/165
for now, or include the patch below which should be upstream soon...

-Eric

> -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(a)cfl.rr.com>
> Signed-off-by: Eric Sandeen <sandeen(a)redhat.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(a)redhat.com>
>> Signed-off-by: "Theodore Ts'o" <tytso(a)mit.edu>
>> Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.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(a)linux.kernel.org
>> http://linux.kernel.org/mailman/listinfo/stable-review
>

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