From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 C832F393DC0 for ; Mon, 30 Mar 2026 20:15:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774901726; cv=none; b=PVG7HUluSfBo+1+OZwqvAoq1/Ad6Ibi2BkmxalupKVhNMnSQJ0VRvfkfMd2eawSsVCWNY/fxjckvzF+7L+AUaNoy6jVSFrrXvvz6u0szc3oOdzJkkENUrDJAAq5m2Te3/BCGkQwqvTkXByzUh33cnxzTnCztTqs2qHZ7mXzjOiU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774901726; c=relaxed/simple; bh=GIdFwH4V271Mu/YGd/0E0a6mBcxaQo79oumlnrXC8oM=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=Fubq/krFOO62qS/xfMOrTJxROdstNx10ZpA3xZKD9RmJM0XMnAsS7Wsvio2P8gSqJffPkxspYwMt8FwUwWzX94yFxxBojMgMfPsnsGfRTprb2Qu3PeJVNczZV/sIx6BxCPbkWjx2h8ihruJh12gRrDYXZgPPKYSpBAR+WI7gFAk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=DXjJrXUQ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="DXjJrXUQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 23289C2BCB0; Mon, 30 Mar 2026 20:15:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1774901726; bh=GIdFwH4V271Mu/YGd/0E0a6mBcxaQo79oumlnrXC8oM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=DXjJrXUQFhraEcid0ADlvzZgeNe5pvalqy/dGOPmBsUe5OqI8MnuhkjVpKerQOhFO u3AaDUOmclDIs3JQP7V8OclSNvaFSZAepXwcODH288IKOKbcAPOGPFDN2LTyNMKytt gsD/AHBc9EHdVGBooD2dysEQ76RdAbO4dnCawfIU= Date: Mon, 30 Mar 2026 13:15:25 -0700 From: Andrew Morton To: Deepanshu Kartikey Cc: muchun.song@linux.dev, osalvador@suse.de, david@kernel.org, mike.kravetz@oracle.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzbot+226c1f947186f8fef796@syzkaller.appspotmail.com Subject: Re: [PATCH] mm/hugetlb: fix hugetlb cgroup rsvd charge/uncharge mismatch Message-Id: <20260330131525.630b8ff8913ade1e0e5c2054@linux-foundation.org> In-Reply-To: <20260328065534.346053-1-kartikey406@gmail.com> References: <20260328065534.346053-1-kartikey406@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sat, 28 Mar 2026 12:25:34 +0530 Deepanshu Kartikey wrote: > In alloc_hugetlb_folio(), a single h_cg pointer is used for both > the rsvd and non-rsvd hugetlb cgroup charges. When map_chg is set, > hugetlb_cgroup_charge_cgroup_rsvd() stores the charged cgroup in > h_cg, but the immediately following hugetlb_cgroup_charge_cgroup() > overwrites h_cg with the non-rsvd cgroup pointer. > > As a result, hugetlb_cgroup_commit_charge_rsvd() stores the wrong > (non-rsvd) cgroup pointer into the folio's rsvd slot. > > When the folio is later freed, free_huge_folio() unconditionally > calls both hugetlb_cgroup_uncharge_folio() and > hugetlb_cgroup_uncharge_folio_rsvd(). The rsvd uncharge reads back > the wrong cgroup from the folio and decrements a counter that was > never charged for that cgroup, causing a page_counter underflow: > > page_counter underflow: -512 nr_pages=512 > WARNING: mm/page_counter.c:61 at page_counter_cancel > > Fix this by introducing a separate h_cg_rsvd pointer exclusively > for the rsvd charge path, keeping the rsvd and non-rsvd charges > fully independent through their charge, commit, and error uncharge > paths. Thanks. > Fixes: 08cf9faf7558 ("hugetlb_cgroup: support noreserve mappings") Merged in 2020! Could reviewers please give consideration to whether we should backport this? > Reported-by: syzbot+226c1f947186f8fef796@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=226c1f947186f8fef796 > Signed-off-by: Deepanshu Kartikey This doesn't seem super-urgent so for now I'll park it in my pile to revisit after 7.1-rc1.