linux-kernel - Re: [PATCH] mm: fix a race scenario in folio_isolate

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Date: Fri, 15 Mar 2024 12:46:29 +0000
From: Matthew Wilcox <willy@...radead.org>
To: "zhaoyang.huang" <zhaoyang.huang@...soc.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Zhaoyang Huang <huangzhaoyang@...il.com>, steve.kang@...soc.com
Subject: Re: [PATCH] mm: fix a race scenario in folio_isolate_lru

On Thu, Mar 14, 2024 at 04:39:21PM +0800, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> 
> Panic[1] reported which is caused by lruvec->list break. Fix the race
> between folio_isolate_lru and release_pages.
> 
> race condition:
> release_pages could meet a non-refered folio which escaped from being
> deleted from LRU but add to another list_head

I don't think the bug is in folio_isolate_lru() but rather in its
caller.

 * Context:
 *
 * (1) Must be called with an elevated refcount on the folio. This is a
 *     fundamental difference from isolate_lru_folios() (which is called
 *     without a stable reference).

So when release_pages() runs, it must not see a refcount decremented to
zero, because the caller of folio_isolate_lru() is supposed to hold one.

Your stack trace is for the thread which is calling release_pages(), not
the one calling folio_isolate_lru(), so I can't help you debug further.