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

[Dan Williams <dan.j.williams@intel.com>]

Bjorn Helgaas wrote:
> On Wed, Jul 26, 2023 at 11:29:42AM -0700, Ira Weiny wrote:
> > 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@wunner.de>
> > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
> 
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> Dan, let me know if you'd rather have me take this.

I have nothing else in the DOE area at this time, so I would be happy if
you took it. It is self contained to drivers/pci/.

Much appreciated.

Acked-by: Dan Williams <dan.j.williams@intel.com>