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nvmf/vfio_user: mitigate cq full race

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Linux host nvme driver processes all pending cqe's in one batch along with
completing backing blk_mq req's and later rings cq_doorbell once for all
processed cqes.
As blk_mq req's are completed there is room for more submissions
before ringing cq_doorbell.

This may race with vfio_user cq_is_full() which uses cq_doorbell to make final
decision and as host has not updated cq_doorbell we fail with cq_full error.

To mitigate this only process commands from sq which have free cq slot.

Signed-off-by: Swapnil Ingle <swapnil.ingle@nutanix.com>
Change-Id: I0cefb41df8099eb71de25923d05a9fcb28e4d124
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/16788
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Community-CI: Mellanox Build Bot
This commit is contained in:
Swapnil Ingle 2023-02-08 09:16:40 +01:00 committed by Tomasz Zawadzki
parent 8613654074
commit 23b518a013
1 changed files with 49 additions and 1 deletions
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50
lib/nvmf/vfio_user.c
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@ -2507,13 +2507,34 @@ consume_cmd(struct nvmf_vfio_user_ctrlr *ctrlr, struct nvmf_vfio_user_sq *sq,
return handle_cmd_req(ctrlr, cmd, sq); return handle_cmd_req(ctrlr, cmd, sq);
} }
static uint32_t
cq_free_slots(struct nvmf_vfio_user_cq *cq)
{
uint32_t free_slots;
assert(cq != NULL);
if (cq->tail == cq->last_head) {
free_slots = cq->size;
} else if (cq->tail > cq->last_head) {
free_slots = cq->size - (cq->tail - cq->last_head);
} else {
free_slots = cq->last_head - cq->tail;
}
assert(free_slots > 0);
return free_slots - 1;
}
/* Returns the number of commands processed, or a negative value on error. */ /* Returns the number of commands processed, or a negative value on error. */
static int static int
handle_sq_tdbl_write(struct nvmf_vfio_user_ctrlr *ctrlr, const uint32_t new_tail, handle_sq_tdbl_write(struct nvmf_vfio_user_ctrlr *ctrlr, const uint32_t new_tail,
struct nvmf_vfio_user_sq *sq) struct nvmf_vfio_user_sq *sq)
{ {
struct spdk_nvme_cmd *queue; struct spdk_nvme_cmd *queue;
struct nvmf_vfio_user_cq *cq = ctrlr->cqs[sq->cqid];
int count = 0; int count = 0;
uint32_t free_cq_slots;
assert(ctrlr != NULL); assert(ctrlr != NULL);
assert(sq != NULL); assert(sq != NULL);
@ -2526,11 +2547,38 @@ handle_sq_tdbl_write(struct nvmf_vfio_user_ctrlr *ctrlr, const uint32_t new_tail
sq->need_rearm = true; sq->need_rearm = true;
} }
free_cq_slots = cq_free_slots(cq);
queue = q_addr(&sq->mapping); queue = q_addr(&sq->mapping);
while (*sq_headp(sq) != new_tail) { while (*sq_headp(sq) != new_tail) {
int err; int err;
struct spdk_nvme_cmd *cmd = &queue[*sq_headp(sq)]; struct spdk_nvme_cmd *cmd;
/*
* Linux host nvme driver can submit cmd's more than free cq slots
* available. So process only those who have cq slots available.
*/
if (free_cq_slots-- == 0) {
cq->last_head = *cq_dbl_headp(cq);
free_cq_slots = cq_free_slots(cq);
if (free_cq_slots > 0) {
continue;
}
/*
* If there are no free cq slots then kick interrupt FD to loop
* again to process remaining sq cmds.
* In case of polling mode we will process remaining sq cmds during
* next polling interation.
* sq head is advanced only for consumed commands.
*/
if (in_interrupt_mode(ctrlr->transport)) {
eventfd_write(ctrlr->intr_fd, 1);
}
break;
}
cmd = &queue[*sq_headp(sq)];
count++; count++;
/* /*