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virtio_random(8): avoid deadlock at shutdown time

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FreeBSD 13+ running as virtual guest may load virtio_random(8) driver
by means of devd(8) unless the driver is blacklisted or disabled
via device.hints(5). Currently, the driver may prevent
the system from rebooting or shutting down correctly.

This change deactivates virtio_random at very late stage
during system shutdown sequence to avoid deadlock
that results in kernel hang.

PR:		253175
Tested by:	tom
MFC after:	3 days
This commit is contained in:
Eugene Grosbein 2022-03-16 11:41:51 +07:00
parent ed5d608911
commit adbf7727b3
1 changed files with 35 additions and 0 deletions
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35
sys/dev/virtio/random/virtio_random.c
View File

@ -32,6 +32,8 @@
__FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/types.h>
#include <sys/eventhandler.h>
#include <sys/kernel.h>
#include <sys/malloc.h>
#include <sys/module.h>
@ -52,6 +54,8 @@ struct vtrnd_softc {
device_t vtrnd_dev;
uint64_t vtrnd_features;
struct virtqueue *vtrnd_vq;
eventhandler_tag eh;
bool inactive;
};
static int vtrnd_modevent(module_t, int, void *);
@ -59,6 +63,7 @@ static int vtrnd_modevent(module_t, int, void *);
static int vtrnd_probe(device_t);
static int vtrnd_attach(device_t);
static int vtrnd_detach(device_t);
static int vtrnd_shutdown(device_t);
static int vtrnd_negotiate_features(struct vtrnd_softc *);
static int vtrnd_setup_features(struct vtrnd_softc *);
@ -86,6 +91,7 @@ static device_method_t vtrnd_methods[] = {
DEVMETHOD(device_probe, vtrnd_probe),
DEVMETHOD(device_attach, vtrnd_attach),
DEVMETHOD(device_detach, vtrnd_detach),
DEVMETHOD(device_shutdown, vtrnd_shutdown),
DEVMETHOD_END
};
@ -160,6 +166,16 @@ vtrnd_attach(device_t dev)
error = EEXIST;
goto fail;
}
sc->eh = EVENTHANDLER_REGISTER(shutdown_post_sync,
vtrnd_shutdown, dev, SHUTDOWN_PRI_LAST + 1); /* ??? */
if (sc->eh == NULL) {
device_printf(dev, "Shutdown event registration failed\n");
error = ENXIO;
goto fail;
}
sc->inactive = false;
random_source_register(&random_vtrnd);
fail:
@ -179,11 +195,27 @@ vtrnd_detach(device_t dev)
atomic_load_explicit(&g_vtrnd_softc, memory_order_acquire) == sc,
("only one global instance at a time"));
sc->inactive = true;
if (sc->eh != NULL) {
EVENTHANDLER_DEREGISTER(shutdown_post_sync, sc->eh);
sc->eh = NULL;
}
random_source_deregister(&random_vtrnd);
atomic_store_explicit(&g_vtrnd_softc, NULL, memory_order_release);
return (0);
}
static int
vtrnd_shutdown(device_t dev)
{
struct vtrnd_softc *sc;
sc = device_get_softc(dev);
sc->inactive = true;
return(0);
}
static int
vtrnd_negotiate_features(struct vtrnd_softc *sc)
{
@ -235,6 +267,9 @@ vtrnd_harvest(struct vtrnd_softc *sc, void *buf, size_t *sz)
_Static_assert(sizeof(value) < PAGE_SIZE, "sglist assumption");
if (sc->inactive)
return (EDEADLK);
sglist_init(&sg, 1, segs);
error = sglist_append(&sg, value, *sz);
if (error != 0)