On 07/14/2011 10:56 PM, liubo wrote:
> On 07/15/2011 01:26 AM, Josef Bacik wrote:
>> Hit this nice little deadlock. What happens is this
>>
>> __btrfs_end_transaction with throttle set, --use_count so it equals 0
>> btrfs_commit_transaction
>> <somebody else actually manages to start the commit>
>> btrfs_end_transaction --use_count so now its -1 <== BAD
>> we just return and wait on the transaction
>>
>> This is bad because we just return after our use_count is -1 and don't let go
>> of our num_writer count on the transaction, so the guy committing the
>> transaction just sits there forever. Fix this by inc'ing our use_count if we're
>> going to call commit_transaction so that if we call btrfs_end_transaction it's
>> valid. Thanks,
>>
>> Signed-off-by: Josef Bacik <josef@xxxxxxxxxx>
>> ---
>> fs/btrfs/transaction.c | 13 ++++++++++---
>> 1 files changed, 10 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
>> index 654755b..00b81fb5 100644
>> --- a/fs/btrfs/transaction.c
>> +++ b/fs/btrfs/transaction.c
>> @@ -497,10 +497,17 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
>> }
>>
>> if (lock && cur_trans->blocked && !cur_trans->in_commit) {
>> - if (throttle)
>> + if (throttle) {
>> + /*
>> + * We may race with somebody else here so end up having
>> + * to call end_transaction on ourselves again, so inc
>> + * our use_count.
>> + */
>> + trans->use_count++;
>> return btrfs_commit_transaction(trans, root);
>> - else
>> + } else {
>> wake_up_process(info->transaction_kthread);
>> + }
>> }
>>
>> WARN_ON(cur_trans != info->running_transaction);
>> @@ -1225,7 +1232,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
>> if (cur_trans->in_commit) {
>> spin_unlock(&cur_trans->commit_lock);
>> atomic_inc(&cur_trans->use_count);
>> - btrfs_end_transaction(trans, root);
>> + __btrfs_end_transaction(trans, root, 0, 1);
>>
>
> Looks good.
>
> BTW, btrfs_end_transaction(trans, root) is just __btrfs_end_transaction(trans, root, 0, 1).
>
Oops you're right, I saw the 1 for lock and thought it was for throttle.
Thanks,
Josef
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