Re: [syzbot] [mm?] INFO: rcu detected stall in purge_vmap_node

[Deepanshu Kartikey]

On Mon, Jan 13, 2026 at 07:08:XX, Hillf Danton wrote:
> Given the test result of your patch, can you specify the root cause
> of the stall reported, Deepanshu?

Hi Hillf,

Thank you for the question. Looking at the stall in the test log, this is
occurring in a different code path from what my patch addresses:

My patch fixes:
  kasan_release_vmalloc_node+0x1ba/0xad0 mm/vmalloc.c:2299
  purge_vmap_node+0x1ba/0xad0

New stall location:
  __reset_page_owner+0x84/0x1a0
  __free_frozen_pages+0x7df/0x1170
  vfree+0x1fd/0xb50
  cleanup_vm_area_work+0x4c/0x100

The root cause pattern is similar (CONFIG_PAGE_OWNER stack unwinding under
RCU read lock), but manifesting in the page freeing path rather than the
KASAN shadow cleanup path.

My patch specifically addresses the unbounded loop in
kasan_release_vmalloc_node()
where we iterate through large purge_lists. The new stall appears to be in
__reset_page_owner() during page freeing, which would need a separate fix in
that code path.

Should I focus on submitting v2 of my vmalloc fix, or would you prefer I
investigate the page_owner stall as well?

Best regards,
Deepanshu