From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E49A53DA7D2 for ; Thu, 27 Aug 2026 08:17:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787818634; cv=none; b=nD3rat+KefIUaHtl11hV0RAgwPhiO0xnwoRMqoY3UzrrFvDNltOfKf8H+AvtmPpeGdPcgJ/4y0XWSSNLIpq/iD0dp6m42RjnfWEcldHmHTjK14CC5WMqGGqtsR2HcN+U/I2gHU2rr5Axo82HyIAzgMQJ/7NkPflfIcZ6uhtXQt4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787818634; c=relaxed/simple; bh=3v1/IdLNCsT/qBsISOCiyBli6VQz9iDJt7iwfW00B1s=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=J8VQzARaX5Nvi8LSkdI/nAho9W+lotSos/TAD8RHqWbgQFLkUrz7uTKXtXTP4IdBi3DGq4p/0tZNxhcCbz/xtlcwPPW/drzk+obktcW+dwCJ6LLhDWMIjCaoBMnwK4lR6f5SKk0PMZ0+Zbr1P7kfe41RLb+rSP1QDuxvW3Ga/Ro= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Kb3+VZf0; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Kb3+VZf0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EDC0E1F000E9; Thu, 27 Aug 2026 08:17:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787818632; bh=IoV2JLyDthha8SRAUynv+MIxi6zER3ywHmEQ0B1FVZU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Kb3+VZf0uc9hFIhgW8al0piOdE/JqGk3Kq7nxZ23oY2lo8kbzImiw7RY3gKQyIGf3 egGYVWXHOgMkrPimJ7z4RryeJxr4bUze9but/U8U/wUqhRY+4unAJQvzCq76Kj6ccI uTmYJ8ZuSp6Epwm425ch7SAH0A6cGcNQQOsRNVz3lYc9YZs2A9AFohonNK07ozVTSU W7VHt53CL/qm2315HgfsuzMC8jtrtR/WjkPBguh8Wk3GrcqRN3ww0VbKniXISd5wRE ENaQF9nrIOUZ+QO2fI2NsvHb4YveXmDwiTs0i9lbnAm0NSXByY8bwviHpGiztS6Y1Z SAG803NYX3JDA== Message-ID: <62ba2ed2-d030-49d8-8872-d714ca0df8f2@kernel.org> Date: Thu, 27 Aug 2026 10:17:08 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/vmstat: annotate data race for per-cpu pageset fields To: Hui Zhu , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Hui Zhu References: <20260827070546.1336383-1-hui.zhu@linux.dev> From: "Vlastimil Babka (SUSE)" Content-Language: en-US In-Reply-To: <20260827070546.1336383-1-hui.zhu@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/27/26 9:05 AM, Hui Zhu wrote: > From: Hui Zhu > > zoneinfo_show_print() reads pcp->count, pcp->high, pcp->batch, > pcp->high_min, pcp->high_max and the per-cpu stat_threshold while > holding only zone->lock, which does not synchronize these fields. > The writers are the page allocation and free fast paths under > pcp->lock, decay_pcp_high() which updates pcp->high without any > lock, pageset_update() which writes batch/high_min/high_max with > WRITE_ONCE(), and refresh_zone_stat_thresholds() which writes > stat_threshold locklessly. > > The race is benign: the values are only printed to /proc/zoneinfo, > they are naturally aligned integers, and pageset_update() already > documents that users of batch/high_min/high_max must cope with the > fields changing asynchronously. Annotate the reads with data_race(), > following commit af1c31acc853 ("mm/vmstat: annotate data race for > zone->free_area[order].nr_free"). > > Found by KCSAN testing on an older kernel; the same race still > exists on mainline. No functional change intended. > > BUG: KCSAN: data-race in zoneinfo_show_print+0x355/0x520 root/klinux/mm/vmstat.c:1774 > race at unknown origin, with read to 0xffff8e1835410808 of 4 bytes by task 22653 on cpu 12: > zoneinfo_show_print+0x355/0x520 root/klinux/mm/vmstat.c:1774 > walk_zones_in_node root/klinux/mm/vmstat.c:1496 [inline] > zoneinfo_show+0x41/0x70 root/klinux/mm/vmstat.c:1806 > seq_read_iter+0x30c/0x970 root/klinux/fs/seq_file.c:230 > proc_reg_read_iter+0x10c/0x170 root/klinux/fs/proc/inode.c:305 > copy_splice_read+0x2a1/0x4e0 root/klinux/fs/splice.c:365 > do_splice_read root/klinux/fs/splice.c:985 [inline] > do_splice_read+0x139/0x1a0 root/klinux/fs/splice.c:959 > splice_direct_to_actor+0x16b/0x540 root/klinux/fs/splice.c:1089 > do_splice_direct_actor root/klinux/fs/splice.c:1207 [inline] > do_splice_direct+0x10a/0x180 root/klinux/fs/splice.c:1233 > do_sendfile+0x6ea/0x7e0 root/klinux/fs/read_write.c:1363 > __do_sys_sendfile64 root/klinux/fs/read_write.c:1424 [inline] > __se_sys_sendfile64 root/klinux/fs/read_write.c:1410 [inline] > __x64_sys_sendfile64+0x117/0x130 root/klinux/fs/read_write.c:1410 > x64_sys_call+0x1cc7/0x1ee0 root/klinux/./arch/x86/include/generated/asm/syscalls_64.h:41 > do_syscall_x64 root/klinux/arch/x86/entry/common.c:46 [inline] > do_syscall_64+0x75/0x2c0 root/klinux/arch/x86/entry/common.c:76 > entry_SYSCALL_64_after_hwframe+0x76/0xe0 > value changed: 0x000001b2 -> 0x000001b1 > Reported by Kernel Concurrency Sanitizer on: > CPU: 12 PID: 22653 Comm: syz-executor.12 Not tainted 6.6.140+ #672 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 > > Signed-off-by: Hui Zhu Acked-by: Vlastimil Babka (SUSE) > --- > mm/vmstat.c | 17 +++++++++++------ > 1 file changed, 11 insertions(+), 6 deletions(-) > > diff --git a/mm/vmstat.c b/mm/vmstat.c > index cb57714539fb..a3e809c57f29 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -1837,6 +1837,11 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat, > struct per_cpu_zonestat __maybe_unused *pzstats; > > pcp = per_cpu_ptr(zone->per_cpu_pageset, i); > + /* > + * Access to the per-cpu pageset fields is lockless as they > + * are used only for printing purposes. Use data_race to > + * avoid KCSAN warning. > + */ > seq_printf(m, > "\n cpu: %i" > "\n count: %i" > @@ -1845,15 +1850,15 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat, > "\n high_min: %i" > "\n high_max: %i", > i, > - pcp->count, > - pcp->high, > - pcp->batch, > - pcp->high_min, > - pcp->high_max); > + data_race(pcp->count), > + data_race(pcp->high), > + data_race(pcp->batch), > + data_race(pcp->high_min), > + data_race(pcp->high_max)); > #ifdef CONFIG_SMP > pzstats = per_cpu_ptr(zone->per_cpu_zonestats, i); > seq_printf(m, "\n vm stats threshold: %d", > - pzstats->stat_threshold); > + data_race(pzstats->stat_threshold)); > #endif > } > seq_printf(m,