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vhost_net: fix sleeping with preempt-disabled in vhost_net_busy_poll()

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syzbot reported "sleeping function called from invalid context" in
vhost_net_busy_poll().

Commit 0308813724 ("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/1448435489-5949-4-git-send-email-jasowang@redhat.com

From this perspective, migrate_disable() is sufficient here, so replace
preempt_disable() with migrate_disable(), avoiding sleepable accesses
from a preempt-disabled context.

Fixes: 0308813724 ("vhost_net: basic polling support")
Tested-by: syzbot+6985cb8e543ea90ba8ee@syzkaller.appspotmail.com
Reported-by: syzbot+6985cb8e543ea90ba8ee@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/69e6a414.050a0220.24bfd3.002d.GAE@google.com/T/
Signed-off-by: Kohei Enju <kohei@enjuk.jp>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kohei Enju
2026-04-23 11:53:31 -07:00
committed by Jakub Kicinski
parent 076b8cad77
commit e08a9fac5c
1 changed files with 2 additions and 2 deletions
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drivers/vhost/net.c
+2 -2
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@@ -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);