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SubjectRe: [PATCH] ibmvfc: fix command state accounting and stale response detection
Tyrel Datwyler <tyreld@linux.ibm.com> a écrit :

> Prior to commit 1f4a4a19508d ("scsi: ibmvfc: Complete commands outside
> the host/queue lock") responses to commands were completed sequentially
> with the host lock held such that a command had a basic binary state of
> active or free. It was therefore a simple affair of ensuring the
> assocaiated ibmvfc_event to a VIOS response was valid by testing that it
> was not already free. The lock relexation work to complete commands
> outside the lock inadverdently made it a trinary command state such that
> a command is either in flight, received and being completed, or
> completed and now free. This breaks the stale command detection logic as
> a command may be still marked active and been placed on the delayed
> completion list when a second stale response for the same command
> arrives. This can lead to double completions and list corruption. This
> issue was exposed by a recent VIOS regression were a missing memory
> barrier could occasionally result in the ibmvfc client receiveing a
> duplicate response for the same command.
>
> Fix the issue by introducing the atomic ibmvfc_event.active to track the
> trinary state of a command. The state is explicitly set to 1 when a
> command is successfully sent. The CRQ response handlers use
> atomic_dec_if_positive() to test for stale responses and correctly
> transition to the completion state when a active command is received.
> Finally, atomic_dec_and_test() is used to sanity check transistions
> when commands are freed as a result of a completion, or moved to the
> purge list as a result of error handling or adapter reset.
>
> Cc: stable@vger.kernel.org
> Fixes: 1f4a4a19508d ("scsi: ibmvfc: Complete commands outside the
> host/queue lock")
> Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
> ---
> drivers/scsi/ibmvscsi/ibmvfc.c | 19 +++++++++++++++++--
> drivers/scsi/ibmvscsi/ibmvfc.h | 1 +
> 2 files changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/scsi/ibmvscsi/ibmvfc.c b/drivers/scsi/ibmvscsi/ibmvfc.c
> index bee1bec49c09..935b01ee44b7 100644
> --- a/drivers/scsi/ibmvscsi/ibmvfc.c
> +++ b/drivers/scsi/ibmvscsi/ibmvfc.c
> @@ -807,6 +807,13 @@ static int ibmvfc_init_event_pool(struct
> ibmvfc_host *vhost,
> for (i = 0; i < size; ++i) {
> struct ibmvfc_event *evt = &pool->events[i];
>
> + /*
> + * evt->active states
> + * 1 = in flight
> + * 0 = being completed
> + * -1 = free/freed
> + */
> + atomic_set(&evt->active, -1);
> atomic_set(&evt->free, 1);
> evt->crq.valid = 0x80;
> evt->crq.ioba = cpu_to_be64(pool->iu_token + (sizeof(*evt->xfer_iu) * i));
> @@ -1017,6 +1024,7 @@ static void ibmvfc_free_event(struct ibmvfc_event *evt)
>
> BUG_ON(!ibmvfc_valid_event(pool, evt));
> BUG_ON(atomic_inc_return(&evt->free) != 1);
> + BUG_ON(atomic_dec_and_test(&evt->active));

Avoid new BUG_ONs. See
https://www.kernel.org/doc/html/latest/process/deprecated.html

>
> spin_lock_irqsave(&evt->queue->l_lock, flags);
> list_add_tail(&evt->queue_list, &evt->queue->free);
> @@ -1072,6 +1080,12 @@ static void ibmvfc_complete_purge(struct
> list_head *purge_list)
> **/
> static void ibmvfc_fail_request(struct ibmvfc_event *evt, int error_code)
> {
> + /*
> + * Anything we are failing should still be active. Otherwise, it
> + * implies we already got a response for the command and are doing
> + * something bad like double completing it.
> + */
> + BUG_ON(!atomic_dec_and_test(&evt->active));

Same


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