linux-kernel - Re: [PATCH] mm/memory-failure: fix deadlock when hugetlb_optimize

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Date: Wed, 10 Apr 2024 15:52:14 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: Oscar Salvador <osalvador@...e.de>
CC: <akpm@...ux-foundation.org>, <naoya.horiguchi@....com>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/memory-failure: fix deadlock when
 hugetlb_optimize_vmemmap is enabled

On 2024/4/10 0:10, Oscar Salvador wrote:
> On Tue, Apr 09, 2024 at 04:10:22PM +0200, Oscar Salvador wrote:
>> On Sun, Apr 07, 2024 at 04:54:56PM +0800, Miaohe Lin wrote:
>>> In short, below scene breaks the lock dependency chain:
>>>
>>>  memory_failure
>>>   __page_handle_poison
>>>    zone_pcp_disable -- lock(pcp_batch_high_lock)
>>>    dissolve_free_huge_page
>>>     __hugetlb_vmemmap_restore_folio
>>>      static_key_slow_dec
>>>       cpus_read_lock -- rlock(cpu_hotplug_lock)
>>>
>>> Fix this by calling drain_all_pages() instead.
>>>
>>> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
>>
>> Acked-by: Oscar Salvador <osalvador@...e.de>

Thanks.

> 
> On a second though,
> 
> disabling pcp via zone_pcp_disable() was a deterministic approach.
> Now, with drain_all_pages() we drain PCP queues to buddy, but nothing
> guarantees that those pages do not end up in a PCP queue again before we
> the call to take_page_off_budy() if we
> need refilling, right?

AFAICS, iff check_pages_enabled static key is enabled and in hard offline mode,
check_new_pages() will prevent those pages from ending up in a PCP queue again
when refilling PCP list. Because PageHWPoison pages will be taken as 'bad' pages
and skipped when refill PCP list.

> 
> I guess we can live with that because we will let the system know that we
> failed to isolate that page.

We're trying best to isolate that page anyway. :)

Thanks for your thought.
.

> 
>