On 29-06-21, 09:11, Dave Jiang wrote: > Konstantin observed that when descriptors are submitted, the descriptor is > added to the pending list after the submission. This creates a race window > with the slight possibility that the descriptor can complete before it > gets added to the pending list and this window would cause the completion > handler to miss processing the descriptor. > > To address the issue, the addition of the descriptor to the pending list > must be done before it gets submitted to the hardware. However, submitting > to swq with ENQCMDS instruction can cause a failure with the condition of > either wq is full or wq is not "active". > > With the descriptor allocation being the gate to the wq capacity, it is not > possible to hit a retry with ENQCMDS submission to the swq. The only > possible failure can happen is when wq is no longer "active" due to hw > error and therefore we are moving towards taking down the portal. Given > this is a rare condition and there's no longer concern over I/O > performance, the driver can walk the completion lists in order to retrieve > and abort the descriptor. > > The error path will set the descriptor to aborted status. It will take the > work list lock to prevent further processing of worklist. It will do a > delete_all on the pending llist to retrieve all descriptors on the pending > llist. The delete_all action does not require a lock. It will walk through > the acquired llist to find the aborted descriptor while add all remaining > descriptors to the work list since it holds the lock. If it does not find > the aborted descriptor on the llist, it will walk through the work > list. And if it still does not find the descriptor, then it means the > interrupt handler has removed the desc from the llist but is pending on > the work list lock and will process it once the error path releases the > lock. This fails to apply on fixes branch, pls rebase -- ~Vinod
