This is a note to let you know that I've just added the patch titled
nvme: check IO start time when deciding to defer KA
to the 6.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
nvme-check-io-start-time-when-deciding-to-defer-ka.patch
and it can be found in the queue-6.3 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 4b8656ba98c919c219e0469f55c78e42b5f1b498
Author: Uday Shankar <ushankar@xxxxxxxxxxxxxxx>
Date: Thu May 25 12:22:03 2023 -0600
nvme: check IO start time when deciding to defer KA
[ 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@xxxxxxxxxxxxxxx>
Reported-by: Randy Jennings <randyj@xxxxxxxxxxxxxxx>
Signed-off-by: Uday Shankar <ushankar@xxxxxxxxxxxxxxx>
Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
Reviewed-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Keith Busch <kbusch@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 3838a6622c34b..d87b8dfda622a 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -397,7 +397,16 @@ 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)) {
@@ -1200,6 +1209,7 @@ 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 ||
@@ -1218,6 +1228,8 @@ 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 2dd52739236e1..8657811f8b887 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -328,6 +328,7 @@ 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;
