[PATCH] vdpa/mlx5: Fix crash on shutdown for when no ndev exists

[Dragos Tatulea]

The ndev was accessed on shutdown without a check if it actually exists.
This triggered the crash pasted below. This patch simply adds a check
before using ndev.

 BUG: kernel NULL pointer dereference, address: 0000000000000300
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0
 Oops: 0000 [#1] SMP
 CPU: 0 PID: 1 Comm: systemd-shutdow Not tainted 6.5.0-rc2_for_upstream_min_debug_2023_07_17_15_05 #1
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
 RIP: 0010:mlx5v_shutdown+0xe/0x50 [mlx5_vdpa]
 RSP: 0018:ffff8881003bfdc0 EFLAGS: 00010286
 RAX: ffff888103befba0 RBX: ffff888109d28008 RCX: 0000000000000017
 RDX: 0000000000000001 RSI: 0000000000000212 RDI: ffff888109d28000
 RBP: 0000000000000000 R08: 0000000d3a3a3882 R09: 0000000000000001
 R10: 0000000000000000 R11: 0000000000000000 R12: ffff888109d28000
 R13: ffff888109d28080 R14: 00000000fee1dead R15: 0000000000000000
 FS:  00007f4969e0be40(0000) GS:ffff88852c800000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000300 CR3: 00000001051cd006 CR4: 0000000000370eb0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 Call Trace:
  <TASK>
  ? __die+0x20/0x60
  ? page_fault_oops+0x14c/0x3c0
  ? exc_page_fault+0x75/0x140
  ? asm_exc_page_fault+0x22/0x30
  ? mlx5v_shutdown+0xe/0x50 [mlx5_vdpa]
  device_shutdown+0x13e/0x1e0
  kernel_restart+0x36/0x90
  __do_sys_reboot+0x141/0x210
  ? vfs_writev+0xcd/0x140
  ? handle_mm_fault+0x161/0x260
  ? do_writev+0x6b/0x110
  do_syscall_64+0x3d/0x90
  entry_SYSCALL_64_after_hwframe+0x46/0xb0
 RIP: 0033:0x7f496990fb56
 RSP: 002b:00007fffc7bdde88 EFLAGS: 00000206 ORIG_RAX: 00000000000000a9
 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f496990fb56
 RDX: 0000000001234567 RSI: 0000000028121969 RDI: fffffffffee1dead
 RBP: 00007fffc7bde1d0 R08: 0000000000000000 R09: 0000000000000000
 R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
 R13: 00007fffc7bddf10 R14: 0000000000000000 R15: 00007fffc7bde2b8
  </TASK>
 CR2: 0000000000000300
 ---[ end trace 0000000000000000 ]---

Fixes: bc9a2b3e686e ("vdpa/mlx5: Support interrupt bypassing")
Signed-off-by: Dragos Tatulea <dtatulea@xxxxxxxxxx>
---
 drivers/vdpa/mlx5/net/mlx5_vnet.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index 9138ef2fb2c8..e2e7ebd71798 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -3556,7 +3556,8 @@ static void mlx5v_shutdown(struct auxiliary_device *auxdev)
 	mgtdev = auxiliary_get_drvdata(auxdev);
 	ndev = mgtdev->ndev;
 
-	free_irqs(ndev);
+	if (ndev)
+		free_irqs(ndev);
 }
 
 static const struct auxiliary_device_id mlx5v_id_table[] = {
-- 
2.41.0