From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta1.migadu.com (out-181.mta1.migadu.com [95.215.58.181]) (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 7D2242E5429 for ; Fri, 10 Jul 2026 06:51:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783666294; cv=none; b=DyMpM/7fPeLPJEnnu1kruof+ao5Uh8XqP6DZXJQ1Z9bmJdkciqfqexEnJgujbnAdDC/KipAY6jPjqGcfhhSU6VEh8NvApVFGtOFUS/4nvtjCJwvMqd2ZnCOX3zu/AHH3gOd16DgObCVPQ1xo04YNyjd+qH621L3d3rxurdr3BGk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783666294; c=relaxed/simple; bh=hWXnGgtW/6TX3TjEYrSBWQIAGUGSi6vL0QwwBkF7Wh8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hVoitG1eibArx1FEZNU1LBIrJd5JJI/ARWw42Wrcpw0JRF1dNDga+rccC8z+8VP0rPADcu3WNEII8LW/f4rmqQl6NFKsbpFlzeOoFoNnWXn4RgEoOIBwevC9hqBzzBG5BUJPwe+FElwM/1OynoFSzS/FW/r8Vm7rwWo6ATrPrkY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=nivqoX0M; arc=none smtp.client-ip=95.215.58.181 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="nivqoX0M" Message-ID: <4d8e0125-0630-4070-95cd-acec3d626329@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783666290; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=p+EOd49UJOd0Hs2rJAZdYLRfuniqnHdpSf3dvb6ZXso=; b=nivqoX0MCv2W6gMLb6RZcwdDAmRwpMKJJwxNzTU4O8nRQJWfkA3q/hfildPz5E+//ji5oz 9H3wNOmjwHpyu4rslf5Ynxrla3pvDiE7qeQghvjQDPLNE8fT/k3LKDsECgz/iAM8Kn1XmR Yb/rTzZTugw4Xlb3vdZ+1c/cUe+YMfs= Date: Fri, 10 Jul 2026 14:51:11 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v5 9/9] mm/page_owner: use memcg_data snapshot instead of PageMemcgKmem() to avoid TOCTOU VM_BUG_ON To: Zi Yan , Vlastimil Babka Cc: Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260701061101.344679-1-ye.liu@linux.dev> <20260701061101.344679-10-ye.liu@linux.dev> <0E890CCC-818A-47DE-9D1C-9EEF98CC758D@nvidia.com> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Ye Liu In-Reply-To: <0E890CCC-818A-47DE-9D1C-9EEF98CC758D@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 在 2026/7/2 10:02, Zi Yan 写道: > On 1 Jul 2026, at 2:10, Ye Liu wrote: > >> print_page_owner_memcg() takes a snapshot of page->memcg_data via >> READ_ONCE at the top of the function and guards against tail pages >> and NULL memcg_data. However, at the end it calls PageMemcgKmem(page) >> which internally calls folio_memcg_kmem() — and that function re-reads >> folio->memcg_data and page->compound_head locklessly, wrapping both >> in VM_BUG_ON assertions: >> >> VM_BUG_ON_PGFLAGS(PageTail(&folio->page), &folio->page); >> VM_BUG_ON_FOLIO(folio->memcg_data & MEMCG_DATA_OBJEXTS, folio); >> >> If the page is concurrently freed and reallocated as a THP tail page >> or a slab page between the initial guards and this final call, the >> VM_BUG_ON assertions can fire on debug builds (CONFIG_DEBUG_VM=y), >> causing a kernel panic. >> >> Fix by reusing the memcg_data snapshot already taken at function entry >> instead of calling PageMemcgKmem(), which is semantically equivalent: >> PageMemcgKmem()->folio_memcg_kmem()->folio->memcg_data & MEMCG_DATA_KMEM. >> This avoids both the TOCTOU window and the assertions entirely. >> >> Signed-off-by: Ye Liu >> --- >> mm/page_owner.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> > LGTM. > > Reviewed-by: Zi Yan Hi,Zi,Vlastimil This patch still has warnings (see sashiko link[1]). I've made the following modifications, or do you have any better suggestions? [1]:https://sashiko.dev/#/patchset/20260701061101.344679-1-ye.liu@linux.dev diff --git a/mm/page_owner.c b/mm/page_owner.c index 2e3880053a34..e18512a49e38 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -540,6 +540,7 @@ static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret, struct page *page) { unsigned long memcg_data; + struct obj_cgroup *objcg; struct mem_cgroup *memcg; bool online; char name[80]; @@ -549,11 +550,14 @@ static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret, if (!memcg_data || PageTail(page)) goto out_unlock; - if (memcg_data & MEMCG_DATA_OBJEXTS) + if (memcg_data & MEMCG_DATA_OBJEXTS) { ret += scnprintf(kbuf + ret, count - ret, "Slab cache page\n"); + goto out_unlock; + } - memcg = page_memcg_check(page); + objcg = (void *)(memcg_data & ~OBJEXTS_FLAGS_MASK); + memcg = objcg ? obj_cgroup_memcg(objcg) : NULL; if (!memcg) goto out_unlock; @@ -561,7 +565,7 @@ static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret, cgroup_name(memcg->css.cgroup, name, sizeof(name)); ret += scnprintf(kbuf + ret, count - ret, "Charged %sto %smemcg %s\n", - PageMemcgKmem(page) ? "(via objcg) " : "", + (memcg_data & MEMCG_DATA_KMEM) ? "(via objcg) " : "", online ? "" : "offline ", name); out_unlock: > > Best Regards, > Yan, Zi -- Thanks, Ye Liu