linux-kernel - Re: [PATCH] mm: migrate: restore the nmask after successfully allocating on the target node

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Message-ID: <80bbb67e8d524aad97fecc99d1eebd52@inspur.com>
Date: Tue, 1 Apr 2025 01:06:32 +0000
From: Simon Wang (王传国) <wangchuanguo@...pur.com>
To: Oscar Salvador <osalvador@...e.de>
CC: "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mhiramat@...nel.org" <mhiramat@...nel.org>, "linux-mm@...ck.org"
	<linux-mm@...ck.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: migrate: restore the nmask after successfully
 allocating on the  target node



> 
> On Wed, Mar 26, 2025 at 11:12:18AM +0800, wangchuanguo wrote:
> > If memory is successfully allocated on the target node and the
> > function directly returns without value restore for nmask, non-first
> > migration operations in migrate_pages() by again label may ignore the
> > nmask settings, thereby allowing new memory allocations for migration
> > on any node.
> >
> > Signed-off-by: wangchuanguo <wangchuanguo@...pur.com>
> 
> Unless I am missing something this looks reasonable, but I whonder why
> nobody noticed it before.
> It is a path that should be pretty exercised.
> 
> 
> --
> Oscar Salvador
> SUSE Labs
I tested it, and even when the nmask is set to all zeros, memory allocation still occurs on other nodes. 
I suspect this is because the bug expands the range of eligible nodes for memory allocation instead of causing allocation failures, which is why it has gone unnoticed.