From: Jan Kara Date: Tue, 4 Jun 2013 16:22:15 +0000 (-0400) Subject: jbd2: fix race in t_outstanding_credits update in jbd2_journal_extend() X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=fe1e8db598b259eafdffbe3dd5fe849cd2ad97d5;p=linux-beck.git jbd2: fix race in t_outstanding_credits update in jbd2_journal_extend() 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. Reviewed-by: Zheng Liu Signed-off-by: Jan Kara Signed-off-by: "Theodore Ts'o" --- diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c index f9cd43190b43..f14288b04042 100644 --- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -433,11 +433,13 @@ 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; } @@ -445,6 +447,7 @@ 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; } @@ -456,7 +459,6 @@ 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);