PCI/DOE: Fix destroy_work_on_stack() race

[ Upstream commit e3a3a09 ]

The following debug object splat was observed in testing:

  ODEBUG: free active (active state 0) object: 0000000097d23782 object type: work_struct hint: doe_statemachine_work+0x0/0x510
  WARNING: CPU: 1 PID: 71 at lib/debugobjects.c:514 debug_print_object+0x7d/0xb0
  ...
  Workqueue: pci 0000:36:00.0 DOE [1 doe_statemachine_work
  RIP: 0010:debug_print_object+0x7d/0xb0
  ...
  Call Trace:
   ? debug_print_object+0x7d/0xb0
   ? __pfx_doe_statemachine_work+0x10/0x10
   debug_object_free.part.0+0x11b/0x150
   doe_statemachine_work+0x45e/0x510
   process_one_work+0x1d4/0x3c0

This occurs because destroy_work_on_stack() was called after signaling
the completion in the calling thread.  This creates a race between
destroy_work_on_stack() and the task->work struct going out of scope in
pci_doe().

Signal the work complete after destroying the work struct.  This is safe
because signal_task_complete() is the final thing the work item does and
the workqueue code is careful not to access the work struct after.

Fixes: abf04be ("PCI/DOE: Fix memory leak with CONFIG_DEBUG_OBJECTS=y")
Link: https://lore.kernel.org/r/20230726-doe-fix-v1-1-af07e614d4dd@intel.com
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/pci/doe.c

@@ -223,8 +223,8 @@ static int pci_doe_recv_resp(struct pci_doe_mb *doe_mb, struct pci_doe_task *tas
 static void signal_task_complete(struct pci_doe_task *task, int rv)
 {
 	task->rv = rv;
-	task->complete(task);
 	destroy_work_on_stack(&task->work);
+	task->complete(task);
 }
 
 static void signal_task_abort(struct pci_doe_task *task, int rv)