Re: [PATCH 2/2] btrfs: fix deadlock when doing reservation

[Mitch Harder <mitch.harder@sabayonlinux.org>]

On Thu, Jun 16, 2011 at 9:52 AM, Josef Bacik <josef@redhat.com> wrote:
> On 06/16/2011 10:36 AM, Mitch Harder wrote:
>> 2011/6/15 Josef Bacik <josef@redhat.com>:
>>> On 06/15/2011 06:47 AM, Miao Xie wrote:
>>>> The following deadlock may happen when doing reservation for metad=
ata:
>>>>
>>>> Task0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Flush thread=
 =A0 =A0 =A0 =A0 =A0 =A0Task1
>>>> start_transaction()
>>>> =A0 shrink_delalloc()
>>>> =A0 =A0 writeback_inodes_sb_nr()
>>>> =A0 =A0 =A0 wait for flush thread
>>>> =A0 =A0 =A0 end.
>>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 btrfs_=
writepages()
>>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 co=
w_file_range()
>>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 btrfs_commit_transaction
>>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 wait num_writer =3D=3D 1
>>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 (wait Task0 end
>>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0transaction)
>>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 st=
art_transaction()
>>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 wait trans commit
>>>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 end
>>>>
>>>> Task0 -> Flush thread -> Task1 -> Task0
>>>>
>>>> Fix the above deadlock by doing reservation before the trans handl=
e has
>>>> been joined into the transaction.
>>>>
>>>> Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
>>>
>>> I've already taken care of this in
>>>
>>> [PATCH 1/2] Btrfs: do transaction space reservation before joining =
the
>>> transaction
>>>
>>> Thanks,
>>>
>>> Josef
>>
>> I've been trying to run down an issue with btrfs freezing with the
>> 3.0_rc btrfs patch set. =A0I've found a test case that repeatably
>> freezes up on my system, and have been surveying the patches on the
>> list to see if the issue has already been resolved.
>>
>> I've been successful in addressing the deadlock by applying Miao Xie=
's
>> patches (I've tested with both "[1/2] btrfs: fix wrong reservation
>> when doing delayed inode operations" and "[2/2] btrfs: fix deadlock
>> when doing reservation").
>>
>> I've only been partially successful in running my test case with Jos=
ef
>> Bacik's patches (the deadlock is cleared; however, now I'm running
>> into a premature ENOSPC).
>>
>> When evaluating Josef's patches, I've applied:
>> Btrfs: account for space reservations properly V2
>> Btrfs: fix btrfs_update_reserved_bytes usage
>> [1/2] Btrfs: do transaction space reservation before joining the tra=
nsaction
>> [2/2] Btrfs: serialize flushers in reserve_metadata_bytes
>>
>
> So drop those first 2, they are wrong and why they are giving you ear=
ly
> enospc. =A0The last two are what you want and should fix your deadloc=
k.
> Thanks,
>

Confirmed.

The deadlock is cleared in my test case when applying just the "[1/2]
Btrfs: do transaction space reservation before joining the
transaction" patch and the "[2/2] Btrfs: serialize flushers in
reserve_metadata_bytes" patch.
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" =
in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html