* [PATCH 0/2] um: time-travel=ext fixes
@ 2020-09-10 9:29 Johannes Berg
2020-09-10 9:29 ` [PATCH 1/2] um: time-travel: fix IRQ handling in time_travel_handle_message() Johannes Berg
2020-09-10 9:29 ` [PATCH 2/2] um: time-travel: return the sequence number in ACK messages Johannes Berg
0 siblings, 2 replies; 3+ messages in thread
From: Johannes Berg @ 2020-09-10 9:29 UTC (permalink / raw)
To: linux-um
Hi,
I had been noticing some hangs in my simulations, and finally had
enough time (and a machine that they reproduce on easily - it's a
timing thing) to debug, so two small fixes for this.
johannes
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^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH 1/2] um: time-travel: fix IRQ handling in time_travel_handle_message()
2020-09-10 9:29 [PATCH 0/2] um: time-travel=ext fixes Johannes Berg
@ 2020-09-10 9:29 ` Johannes Berg
2020-09-10 9:29 ` [PATCH 2/2] um: time-travel: return the sequence number in ACK messages Johannes Berg
1 sibling, 0 replies; 3+ messages in thread
From: Johannes Berg @ 2020-09-10 9:29 UTC (permalink / raw)
To: linux-um; +Cc: Johannes Berg
From: Johannes Berg <johannes.berg@intel.com>
As the comment here indicates, we need to do the polling in the
idle loop without blocking interrupts, since interrupts can be
vhost-user messages that we must process even while in our idle
loop.
I don't know why I explained one thing and implemented another,
but we have indeed observed random hangs due to this, depending
on the timing of the messages.
Fixes: 88ce64249233 ("um: Implement time-travel=ext")
Change-Id: Ic74385f3d36466cc01cc8487fc54affe0fdf7f26
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
arch/um/kernel/time.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c
index 25eaa6a0c658..c07436e89e59 100644
--- a/arch/um/kernel/time.c
+++ b/arch/um/kernel/time.c
@@ -70,13 +70,17 @@ static void time_travel_handle_message(struct um_timetravel_msg *msg,
* read of the message and write of the ACK.
*/
if (mode != TTMH_READ) {
+ bool disabled = irqs_disabled();
+
+ BUG_ON(mode == TTMH_IDLE && !disabled);
+
+ if (disabled)
+ local_irq_enable();
while (os_poll(1, &time_travel_ext_fd) != 0) {
- if (mode == TTMH_IDLE) {
- BUG_ON(!irqs_disabled());
- local_irq_enable();
- local_irq_disable();
- }
+ /* nothing */
}
+ if (disabled)
+ local_irq_disable();
}
ret = os_read_file(time_travel_ext_fd, msg, sizeof(*msg));
--
2.26.2
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^ permalink raw reply related [flat|nested] 3+ messages in thread
* [PATCH 2/2] um: time-travel: return the sequence number in ACK messages
2020-09-10 9:29 [PATCH 0/2] um: time-travel=ext fixes Johannes Berg
2020-09-10 9:29 ` [PATCH 1/2] um: time-travel: fix IRQ handling in time_travel_handle_message() Johannes Berg
@ 2020-09-10 9:29 ` Johannes Berg
1 sibling, 0 replies; 3+ messages in thread
From: Johannes Berg @ 2020-09-10 9:29 UTC (permalink / raw)
To: linux-um; +Cc: Johannes Berg
From: Johannes Berg <johannes.berg@intel.com>
For external time travel, the protocol says to return the
incoming sequence number in the ACK message to aid debugging,
so do that.
Change-Id: Ib2bcca1371247b2f8643f35fb85ca5051addd8cc
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
arch/um/kernel/time.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c
index c07436e89e59..3d109ff3309b 100644
--- a/arch/um/kernel/time.c
+++ b/arch/um/kernel/time.c
@@ -106,6 +106,7 @@ static void time_travel_handle_message(struct um_timetravel_msg *msg,
break;
}
+ resp.seq = msg->seq;
os_write_file(time_travel_ext_fd, &resp, sizeof(resp));
}
--
2.26.2
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