On Mon, Apr 08, 2013 at 11:32:15PM +0200, Jan Kara wrote:
> jbd2_journal_extend() first checked whether transaction can accept extending
> handle with more credits and then added credits to t_outstanding_credits.
> This can race with start_this_handle() adding another handle to a transaction
> and thus overbooking a transaction. Make jbd2_journal_extend() use
> atomic_add_return() to close the race.
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Zheng Liu <wenqing.lz@xxxxxxxxxx>
Regards,
- Zheng
> ---
> fs/jbd2/transaction.c | 6 ++++--
> 1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index aee40c9..9639e47 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -434,11 +434,13 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
> }
>
> spin_lock(&transaction->t_handle_lock);
> - wanted = atomic_read(&transaction->t_outstanding_credits) + nblocks;
> + wanted = atomic_add_return(nblocks,
> + &transaction->t_outstanding_credits);
>
> if (wanted > journal->j_max_transaction_buffers) {
> jbd_debug(3, "denied handle %p %d blocks: "
> "transaction too large\n", handle, nblocks);
> + atomic_sub(nblocks, &transaction->t_outstanding_credits);
> goto unlock;
> }
>
> @@ -446,6 +448,7 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
> jbd2_log_space_left(journal)) {
> jbd_debug(3, "denied handle %p %d blocks: "
> "insufficient log space\n", handle, nblocks);
> + atomic_sub(nblocks, &transaction->t_outstanding_credits);
> goto unlock;
> }
>
> @@ -457,7 +460,6 @@ int jbd2_journal_extend(handle_t *handle, int nblocks)
>
> handle->h_buffer_credits += nblocks;
> handle->h_requested_credits += nblocks;
> - atomic_add(nblocks, &transaction->t_outstanding_credits);
> result = 0;
>
> jbd_debug(3, "extended handle %p by %d\n", handle, nblocks);
> --
> 1.7.1
>
> --
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