[PATCH] PCI/DOE: Fix destroy_work_on_stack() race

[Ira Weiny]

The following debug object splat was observed in testing.

  [   14.061937] ------------[ cut here ]------------
  [   14.063899] ODEBUG: free active (active state 0) object: 0000000097d23782 object type: work_struct hint: doe_statemachine_work+0x0/0x510
  [   14.067480] WARNING: CPU: 1 PID: 71 at lib/debugobjects.c:514 debug_print_object+0x7d/0xb0
  ...
  [   14.080951] Workqueue: pci 0000:36:00.0 DOE [1 doe_statemachine_work
  [   14.083485] RIP: 0010:debug_print_object+0x7d/0xb0
  ...
  [   14.116231] Call Trace:
  [   14.117652]  <TASK>
  [   14.118958]  ? debug_print_object+0x7d/0xb0
  [   14.120782]  ? __warn+0x7d/0x130
  [   14.122399]  ? debug_print_object+0x7d/0xb0
  [   14.123746]  ? report_bug+0x18d/0x1c0
  [   14.125025]  ? handle_bug+0x3c/0x80
  [   14.126506]  ? exc_invalid_op+0x13/0x60
  [   14.127796]  ? asm_exc_invalid_op+0x16/0x20
  [   14.129380]  ? debug_print_object+0x7d/0xb0
  [   14.130688]  ? debug_print_object+0x7d/0xb0
  [   14.131997]  ? __pfx_doe_statemachine_work+0x10/0x10
  [   14.133597]  debug_object_free.part.0+0x11b/0x150
  [   14.134940]  doe_statemachine_work+0x45e/0x510
  [   14.136348]  process_one_work+0x1d4/0x3c0
  ...
  [   14.161484]  </TASK>
  [   14.162434] ---[ end trace 0000000000000000 ]---

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 of scope in the
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: abf04be0e707 ("PCI/DOE: Fix memory leak with CONFIG_DEBUG_OBJECTS=y")
Cc: Lukas Wunner <lukas@xxxxxxxxx>
Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
---
 drivers/pci/doe.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c
index 1b97a5ab71a9..e3aab5edaf70 100644
--- a/drivers/pci/doe.c
+++ b/drivers/pci/doe.c
@@ -293,8 +293,8 @@ 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)

---
base-commit: 20ea1e7d13c1b544fe67c4a8dc3943bb1ab33e6f
change-id: 20230726-doe-fix-f57943f9ea82

Best regards,
-- 
Ira Weiny <ira.weiny@xxxxxxxxx>