linux-kernel - Re: [syzbot] [mm?] INFO: rcu detected stall in purge_vmap

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Message-ID: <CADhLXY7-56WHoQcQAiwFHf2y80WBd+1G7veU9EoZCKXuFXXPhA@mail.gmail.com>
Date: Mon, 12 Jan 2026 20:20:45 +0530
From: Deepanshu Kartikey <kartikey406@...il.com>
To: Hillf Danton <hdanton@...a.com>
Cc: syzbot <syzbot+d8d4c31d40f868eaea30@...kaller.appspotmail.com>, 
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	syzkaller-bugs@...glegroups.com, urezki@...il.com
Subject: Re: [syzbot] [mm?] INFO: rcu detected stall in purge_vmap_node

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