linux-kernel - [PATCH] mm/page_alloc: make percpu_pagelist_high

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>] [day] [month] [year] [list]

Message-ID: <20251201060009.1420792-1-aboorvad@linux.ibm.com>
Date: Mon,  1 Dec 2025 11:30:09 +0530
From: Aboorva Devarajan <aboorvad@...ux.ibm.com>
To: akpm@...ux-foundation.org, vbabka@...e.cz, surenb@...gle.com,
        mhocko@...e.com, jackmanb@...gle.com, hannes@...xchg.org,
        ziy@...dia.com
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, aboorvad@...ux.ibm.com
Subject: [PATCH] mm/page_alloc: make percpu_pagelist_high_fraction reads lock-free

When page isolation loops indefinitely during memory offline, reading
/proc/sys/vm/percpu_pagelist_high_fraction blocks on pcp_batch_high_lock,
causing hung task warnings.

Make procfs reads lock-free since percpu_pagelist_high_fraction is a simple
integer with naturally atomic reads, writers still serialize via the mutex.

This prevents hung task warnings when reading the procfs file during
long-running memory offline operations.

Signed-off-by: Aboorva Devarajan <aboorvad@...ux.ibm.com>
---
 mm/page_alloc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ed82ee55e66a..7c8d773ed4af 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6611,11 +6611,14 @@ static int percpu_pagelist_high_fraction_sysctl_handler(const struct ctl_table *
 	int old_percpu_pagelist_high_fraction;
 	int ret;
 
+	if (!write)
+		return proc_dointvec_minmax(table, write, buffer, length, ppos);
+
 	mutex_lock(&pcp_batch_high_lock);
 	old_percpu_pagelist_high_fraction = percpu_pagelist_high_fraction;
 
 	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
-	if (!write || ret < 0)
+	if (ret < 0)
 		goto out;
 
 	/* Sanity checking to avoid pcp imbalance */
-- 
2.50.1