syzbot reported "sleeping function called from invalid context" in
vhost_net_busy_poll().
Commit 030881372460 ("vhost_net: basic polling support") introduced a
busy-poll loop and preempt_{disable,enable}() around it, where each
iteration calls a sleepable function inside the loop.
The purpose of disabling preemption was to keep local_clock()-based
timeout accounting on a single CPU, rather than as a requirement of
busy-poll itself:
https://lore.kernel.org/netdev/[email protected]/T/#u
Changes from RFC V1:
...
- Disable preemption during busy looping to make sure local_clock()
was correctly used.
>From this perspective, migrate_disable() is sufficient here, so replace
preempt_disable() with migrate_disable(), avoiding sleepable accesses
from a preempt-disabled context.
Fixes: 030881372460 ("vhost_net: basic polling support")
Tested-by: [email protected]
Reported-by: [email protected]
Closes:
https://lore.kernel.org/all/[email protected]/T/
Signed-off-by: Kohei Enju <[email protected]>
---
drivers/vhost/net.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 80965181920c..c6536cad9c4f 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -560,7 +560,7 @@ static void vhost_net_busy_poll(struct vhost_net *net,
busyloop_timeout = poll_rx ? rvq->busyloop_timeout:
tvq->busyloop_timeout;
- preempt_disable();
+ migrate_disable();
endtime = busy_clock() + busyloop_timeout;
while (vhost_can_busy_poll(endtime)) {
@@ -577,7 +577,7 @@ static void vhost_net_busy_poll(struct vhost_net *net,
cpu_relax();
}
- preempt_enable();
+ migrate_enable();
if (poll_rx || sock_has_rx_data(sock))
vhost_net_busy_poll_try_queue(net, vq);
--
2.51.0
