>>>>> Stephen C Tweedie (SCT) writes:
>> + /* return credit back to the handle if it was really spent */
>> + if (credits)
>> + handle->h_buffer_credits++;
>> + jh->b_tcount--;
>> + if (jh->b_tcount == 0) {
>> + /*
>> + * this was last reference to the block from the current
>> + * transaction and we'd like to return credit to the
>> + * whole transaction -bzzz
>> + */
>> + if (!credits)
>> + handle->h_buffer_credits++;
SCT> I think there's a problem here.
SCT> What if:
SCT> Process A gets write access, and is the first to do so (*credits=1)
SCT> Processes B gets write access (*credits=0)
SCT> B modifies the buffer and finishes
SCT> A looks again, sees B's modifications, and releases the buffer because
SCT> it's no use any more.
SCT> Now, B's release didn't return credits. The bh is part of the
SCT> transaction and was not released.
hmmm. that's a good catch. so, with this patch A increments h_buffer_credits
and this one will go to the t_outstanding_credits while the buffer is still
part of the transaction. indeed, an imbalance.
probably something like the following would be enough?
+ /* return credit back to the handle if it was really spent */
+ if (credits) {
+ handle->h_buffer_credits++;
+ spin_lock(&handle->h_transaction->t_handle_lock);
+ handle->h_transaction->t_outstanding_credits++;
+ spin_lock(&handle->h_transaction->t_handle_lock);
+ }
thanks, Alex
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