linux-kernel - Re: [PATCH v2] mm/page_alloc: Report 1 as zone_batchsize for !CONFIG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <c73056fc-94f1-435a-8418-26506cba9de7@roeck-us.net>
Date: Thu, 18 Dec 2025 07:39:50 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Joshua Hahn <joshua.hahnjy@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Palmer <daniel@...f.com>,
	Brendan Jackman <jackmanb@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Zi Yan <ziy@...dia.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kernel-team@...a.com
Subject: Re: [PATCH v2] mm/page_alloc: Report 1 as zone_batchsize for
 !CONFIG_MMU

On Thu, Dec 18, 2025 at 12:31:59AM -0800, Joshua Hahn wrote:
> Commit 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0")
> moved the error handling (0-handling) of zone_batchsize from its
> callers to inside the function. However, the commit left out the error
> handling for the NOMMU case, leading to deadlocks on NOMMU systems.
> 
> For NOMMU systems, return 1 instead of 0 for zone_batchsize, which restores
> the previous deadlock-free behavior.
> 
> There is no functional difference expected with this patch before commit
> 2783088ef24e, other than the pr_debug in zone_pcp_init now printing out
> 1 instead of 0 for zones in NOMMU systems. Not only is this a pr_debug,
> the difference is purely semantic anyways.
> 
> Fixes: 2783088ef24e ("mm/page_alloc: prevent reporting pcp->batch = 0")
> Reported-by: Daniel Palmer <daniel@...ngy.jp>
> Closes: https://lore.kernel.org/linux-mm/CAFr9PX=_HaM3_xPtTiBn5Gw5-0xcRpawpJ02NStfdr0khF2k7g@mail.gmail.com/
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Closes: https://lore.kernel.org/all/42143500-c380-41fe-815c-696c17241506@roeck-us.net/
> Signed-off-by: Joshua Hahn <joshua.hahnjy@...il.com>

Tested-by: Guenter Roeck <linux@...ck-us.net>

Guenter