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um: time-travel: Fix IRQ handling in time_travel_handle_message()

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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")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
This commit is contained in:
Johannes Berg 2020-09-10 11:31:12 +02:00 committed by Richard Weinberger
parent 730586ff7f
commit ebef8ea2ba
1 changed files with 9 additions and 5 deletions
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14
arch/um/kernel/time.c
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@ -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));