From: Uday Shankar ushankar@purestorage.com
[ Upstream commit 774a9636514764ddc0d072ae0d1d1c01a47e6ddd ]
When a command completes, we set a flag which will skip sending a keep alive at the next run of nvme_keep_alive_work when TBKAS is on. However, if the command was submitted long ago, it's possible that the controller may have also restarted its keep alive timer (as a result of receiving the command) long ago. The following trace demonstrates the issue, assuming TBKAS is on and KATO = 8 for simplicity:
1. t = 0: submit I/O commands A, B, C, D, E 2. t = 0.5: commands A, B, C, D, E reach controller, restart its keep alive timer 3. t = 1: A completes 4. t = 2: run nvme_keep_alive_work, see recent completion, do nothing 5. t = 3: B completes 6. t = 4: run nvme_keep_alive_work, see recent completion, do nothing 7. t = 5: C completes 8. t = 6: run nvme_keep_alive_work, see recent completion, do nothing 9. t = 7: D completes 10. t = 8: run nvme_keep_alive_work, see recent completion, do nothing 11. t = 9: E completes
At this point, 8.5 seconds have passed without restarting the controller's keep alive timer, so the controller will detect a keep alive timeout.
Fix this by checking the IO start time when deciding to defer sending a keep alive command. Only set comp_seen if the command started after the most recent run of nvme_keep_alive_work. With this change, the completions of B, C, and D will not set comp_seen and the run of nvme_keep_alive_work at t = 4 will send a keep alive.
Reported-by: Costa Sapuntzakis costa@purestorage.com Reported-by: Randy Jennings randyj@purestorage.com Signed-off-by: Uday Shankar ushankar@purestorage.com Reviewed-by: Hannes Reinecke hare@suse.de Reviewed-by: Sagi Grimberg sagi@grimberg.me Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Keith Busch kbusch@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/nvme/host/core.c | 14 +++++++++++++- drivers/nvme/host/nvme.h | 1 + 2 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c index 50a83306bea7b..06dd1c0780bfc 100644 --- a/drivers/nvme/host/core.c +++ b/drivers/nvme/host/core.c @@ -395,7 +395,16 @@ void nvme_complete_rq(struct request *req) trace_nvme_complete_rq(req); nvme_cleanup_cmd(req);
- if (ctrl->kas) + /* + * Completions of long-running commands should not be able to + * defer sending of periodic keep alives, since the controller + * may have completed processing such commands a long time ago + * (arbitrarily close to command submission time). + * req->deadline - req->timeout is the command submission time + * in jiffies. + */ + if (ctrl->kas && + req->deadline - req->timeout >= ctrl->ka_last_check_time) ctrl->comp_seen = true;
switch (nvme_decide_disposition(req)) { @@ -1235,6 +1244,7 @@ static enum rq_end_io_ret nvme_keep_alive_end_io(struct request *rq, return RQ_END_IO_NONE; }
+ ctrl->ka_last_check_time = jiffies; ctrl->comp_seen = false; spin_lock_irqsave(&ctrl->lock, flags); if (ctrl->state == NVME_CTRL_LIVE || @@ -1253,6 +1263,8 @@ static void nvme_keep_alive_work(struct work_struct *work) bool comp_seen = ctrl->comp_seen; struct request *rq;
+ ctrl->ka_last_check_time = jiffies; + if ((ctrl->ctratt & NVME_CTRL_ATTR_TBKAS) && comp_seen) { dev_dbg(ctrl->device, "reschedule traffic based keep-alive timer\n"); diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h index 01d90424af534..ce668268b2c32 100644 --- a/drivers/nvme/host/nvme.h +++ b/drivers/nvme/host/nvme.h @@ -318,6 +318,7 @@ struct nvme_ctrl { struct delayed_work ka_work; struct delayed_work failfast_work; struct nvme_command ka_cmd; + unsigned long ka_last_check_time; struct work_struct fw_act_work; unsigned long events;