From: Johannes Berg johannes.berg@intel.com
[ Upstream commit ebef8ea2ba967026192a26f4529890893919bc57 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 25eaa6a0c6583..c07436e89e599 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));