net: mana: Fix double destroy_workqueue on service rescan PCI path

While testing corner cases in the driver, a use-after-free crash
was found on the service rescan PCI path.

When mana_serv_reset() calls mana_gd_suspend(), mana_gd_cleanup()
destroys gc->service_wq. If the subsequent mana_gd_resume() fails
with -ETIMEDOUT or -EPROTO, the code falls through to
mana_serv_rescan() which triggers pci_stop_and_remove_bus_device().
This invokes the PCI .remove callback (mana_gd_remove), which calls
mana_gd_cleanup() a second time, attempting to destroy the already-
freed workqueue. Fix this by NULL-checking gc->service_wq in
mana_gd_cleanup() and setting it to NULL after destruction.

Call stack of issue for reference:
[Sat Feb 21 18:53:48 2026] Call Trace:
[Sat Feb 21 18:53:48 2026]  <TASK>
[Sat Feb 21 18:53:48 2026]  mana_gd_cleanup+0x33/0x70 [mana]
[Sat Feb 21 18:53:48 2026]  mana_gd_remove+0x3a/0xc0 [mana]
[Sat Feb 21 18:53:48 2026]  pci_device_remove+0x41/0xb0
[Sat Feb 21 18:53:48 2026]  device_remove+0x46/0x70
[Sat Feb 21 18:53:48 2026]  device_release_driver_internal+0x1e3/0x250
[Sat Feb 21 18:53:48 2026]  device_release_driver+0x12/0x20
[Sat Feb 21 18:53:48 2026]  pci_stop_bus_device+0x6a/0x90
[Sat Feb 21 18:53:48 2026]  pci_stop_and_remove_bus_device+0x13/0x30
[Sat Feb 21 18:53:48 2026]  mana_do_service+0x180/0x290 [mana]
[Sat Feb 21 18:53:48 2026]  mana_serv_func+0x24/0x50 [mana]
[Sat Feb 21 18:53:48 2026]  process_one_work+0x190/0x3d0
[Sat Feb 21 18:53:48 2026]  worker_thread+0x16e/0x2e0
[Sat Feb 21 18:53:48 2026]  kthread+0xf7/0x130
[Sat Feb 21 18:53:48 2026]  ? __pfx_worker_thread+0x10/0x10
[Sat Feb 21 18:53:48 2026]  ? __pfx_kthread+0x10/0x10
[Sat Feb 21 18:53:48 2026]  ret_from_fork+0x269/0x350
[Sat Feb 21 18:53:48 2026]  ? __pfx_kthread+0x10/0x10
[Sat Feb 21 18:53:48 2026]  ret_from_fork_asm+0x1a/0x30
[Sat Feb 21 18:53:48 2026]  </TASK>

Fixes: 505cc26 ("net: mana: Add support for auxiliary device servicing events")
Reviewed-by: Haiyang Zhang <[email protected]>
Signed-off-by: Dipayaan Roy <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Link: https://patch.msgid.link/aZ2bzL64NagfyHpg@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net
Signed-off-by: Jakub Kicinski <[email protected]>

Author: Dipayaan Roy

drivers/net/ethernet/microsoft/mana/gdma_main.c

@@ -1946,7 +1946,10 @@ static void mana_gd_cleanup(struct pci_dev *pdev)
 
 	mana_gd_remove_irqs(pdev);
 
-	destroy_workqueue(gc->service_wq);
+	if (gc->service_wq) {
+		destroy_workqueue(gc->service_wq);
+		gc->service_wq = NULL;
+	}
 	dev_dbg(&pdev->dev, "mana gdma cleanup successful\n");
 }
 

drivers/net/ethernet/microsoft/mana/mana_en.c

@@ -3762,7 +3762,9 @@ void mana_rdma_remove(struct gdma_dev *gd)
 	}
 
 	WRITE_ONCE(gd->rdma_teardown, true);
-	flush_workqueue(gc->service_wq);
+
+	if (gc->service_wq)
+		flush_workqueue(gc->service_wq);
 
 	if (gd->adev)
 		remove_adev(gd);