* [PATCH v2] vhost-vdpa: initialize state before publishing cdev
@ 2026-10-11 10:28 Linfeng Sun via B4 Relay
0 siblings, 0 replies; only message in thread
From: Linfeng Sun via B4 Relay @ 2026-10-11 10:28 UTC (permalink / raw)
To: Michael S. Tsirkin, Jason Wang, Eugenio Pérez, Tiwei Bie
Cc: kvm, virtualization, linux-kernel, Linfeng Sun
From: Linfeng Sun <linfeng.sun.dev@gmail.com>
Initialize the completion and as hash buckets before cdev_device_add()
makes the device accessible.
Fixes: 4c8cf31885f6 ("vhost: introduce vDPA-based backend")
Assisted-by: OpenAI-Codex:GPT-5.6
Signed-off-by: Linfeng Sun <linfeng.sun.dev@gmail.com>
---
I used // because b4 ignores lines starting with #. Please uncomment those
lines before reproducing.
---- reproduce.c ----
// #include <fcntl.h>
// #include <pthread.h>
// #include <stdatomic.h>
// #include <unistd.h>
// #define THREADS 16
static const char *device_path;
static const char *sysfs_path;
static atomic_int stop;
static void *open_close(void *unused)
{
(void)unused;
while (!atomic_load(&stop)) {
int fd;
if (access(sysfs_path, F_OK))
continue;
fd = open(device_path, O_RDWR);
if (fd >= 0)
close(fd);
}
return NULL;
}
int main(int argc, char **argv)
{
pthread_t threads[THREADS];
int i;
if (argc != 3)
return 1;
device_path = argv[1];
sysfs_path = argv[2];
for (i = 0; i < THREADS; i++)
if (pthread_create(&threads[i], NULL, open_close, NULL))
return 1;
sleep(45);
atomic_store(&stop, 1);
for (i = 0; i < THREADS; i++)
pthread_join(threads[i], NULL);
return 0;
}
---- crash ----
[ 23.959139] BUG: unable to handle page fault for address: fffffffffffffff8
[ 23.959859] #PF: supervisor read access in kernel mode
[ 23.960291] #PF: error_code(0x0000) - not-present page
[ 23.960740] PGD 4869067 P4D 4869067 PUD 486b067 PMD 0
[ 23.961718] Oops: Oops: 0000 [#1] SMP NOPTI
[ 23.962395] CPU: 1 UID: 0 PID: 126 Comm: poc Not tainted 7.3.0-rc2+ #1 PREEMPT(full)
[ 23.963059] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 23.963890] RIP: 0010:complete+0x44/0x80
[ 23.964656] Code: 41 d8 01 49 89 c4 8b 03 83 f8 ff 74 05 83 c0 01 89 03 48 8b 53 10 48 8d 43 10 48 39 c2 74 29 48 8b 5b 10 31 d2 be 03 00 00 00 <48> 8b 7b f8 e8 e3 65 fc ff 48 8b 13 48 8b 43 08 48 89 42 08 48 89
[ 23.965679] RSP: 0018:ffffc9000141bc38 EFLAGS: 00000046
[ 23.966109] RAX: ffff888008a678d8 RBX: 0000000000000000 RCX: 0000000000000000
[ 23.966513] RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000000
[ 23.967005] RBP: ffffc9000141bc50 R08: 0000000000000000 R09: 0000000000000000
[ 23.967483] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000246
[ 23.967896] R13: ffff888008a678d0 R14: 0000000000000000 R15: ffffffff83541780
[ 23.968384] FS: 00007dcd511046c0(0000) GS:ffff8880b94b6000(0000) knlGS:0000000000000000
[ 23.968933] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 23.969398] CR2: fffffffffffffff8 CR3: 0000000009a41000 CR4: 00000000000006f0
[ 23.970091] Call Trace:
[ 23.970735] <TASK>
[ 23.971266] vhost_vdpa_release+0x175/0x190
[ 23.971862] ? __pfx_vhost_vdpa_release+0x10/0x10
[ 23.972298] __fput+0x1c2/0x520
[ 23.972692] fput_close_sync+0x6e/0x140
[ 23.973040] __x64_sys_close+0x51/0xd0
[ 23.973362] x64_sys_call+0x2680/0x27e0
[ 23.973655] do_syscall_64+0xbf/0x550
[ 23.973969] ? restore_fpregs_from_fpstate+0xa1/0x110
[ 23.974322] ? switch_fpu_return+0xbd/0x190
[ 23.974630] ? do_syscall_64+0x299/0x550
[ 23.974962] ? putname+0x7f/0xd0
[ 23.975267] ? do_faccessat+0x3fe/0x570
[ 23.975583] ? __sanitizer_cov_trace_cmp4+0x16/0x30
[ 23.975934] ? fpregs_assert_state_consistent+0x7b/0xc0
[ 23.976272] ? do_syscall_64+0xfd/0x550
[ 23.976591] ? __sanitizer_cov_trace_cmp4+0x16/0x30
[ 23.976949] ? fpregs_assert_state_consistent+0x7b/0xc0
[ 23.977304] ? do_syscall_64+0xfd/0x550
[ 23.977611] ? prandom_u32_state+0xd/0x90
[ 23.977933] ? do_syscall_64+0x31/0x550
[ 23.978248] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 23.978644] RIP: 0033:0x41e94c
[ 23.979296] Code: 0f 05 48 3d 00 f0 ff ff 77 3c c3 0f 1f 00 55 48 89 e5 48 83 ec 10 89 7d fc e8 b0 a5 02 00 8b 7d fc 89 c2 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 2c 89 d7 89 45 fc e8 12 a6 02 00 8b 45 fc c9
[ 23.980064] RSP: 002b:00007dcd51104220 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
[ 23.980511] RAX: ffffffffffffffda RBX: 00007dcd51104cdc RCX: 000000000041e94c
[ 23.980887] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
[ 23.981251] RBP: 00007dcd51104230 R08: 0000000000000000 R09: 00007dcd511046c0
[ 23.981604] R10: 0000000000000000 R11: 0000000000000293 R12: 00007dcd511046c0
[ 23.981960] R13: ffffffffffffffb8 R14: 0000000000000000 R15: 00007ffe8c98a0f0
[ 23.982377] </TASK>
[ 23.982597] Modules linked in:
[ 23.983036] CR2: fffffffffffffff8
[ 23.983847] ---[ end trace 0000000000000000 ]---
---
Changes in v2:
- Block opens until probe completes.
- Link to v1: https://patch.msgid.link/20261011-fix-null-pointer-in-vhost_vdpa_release-v1-1-43ebc225f938@gmail.com
To: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowangio@gmail.com>
To: Eugenio Pérez <eperezma@redhat.com>
To: Tiwei Bie <tiwei.bie@intel.com>
Cc: kvm@vger.kernel.org
Cc: virtualization@lists.linux.dev
Cc: linux-kernel@vger.kernel.org
---
drivers/vhost/vdpa.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index ff7d90719171..6cff1ed2004e 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -1655,7 +1655,7 @@ static int vhost_vdpa_probe(struct vdpa_device *vdpa)
return minor;
}
- atomic_set(&v->opened, 0);
+ atomic_set(&v->opened, 1);
spin_lock_init(&v->config_lock);
v->minor = minor;
v->vdpa = vdpa;
@@ -1678,16 +1678,17 @@ static int vhost_vdpa_probe(struct vdpa_device *vdpa)
cdev_init(&v->cdev, &vhost_vdpa_fops);
v->cdev.owner = THIS_MODULE;
+ init_completion(&v->completion);
+ for (i = 0; i < VHOST_VDPA_IOTLB_BUCKETS; i++)
+ INIT_HLIST_HEAD(&v->as[i]);
r = cdev_device_add(&v->cdev, &v->dev);
if (r)
goto err;
- init_completion(&v->completion);
vdpa_set_drvdata(vdpa, v);
- for (i = 0; i < VHOST_VDPA_IOTLB_BUCKETS; i++)
- INIT_HLIST_HEAD(&v->as[i]);
+ atomic_set_release(&v->opened, 0);
return 0;
---
base-commit: c69023b5e16e5ffe9368603dca76d85bd544ee57
change-id: 20261011-fix-null-pointer-in-vhost_vdpa_release-b495fb89aaa8
Best regards,
--
Linfeng Sun <linfeng.sun.dev@gmail.com>
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