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 599D5324B32; Wed, 22 Apr 2026 15:50:45 +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=1776873045; cv=none; b=pwW/aVvU8WM9Uczfh+5N6KDXJZ+8eWAeygx85Sx394M0lUO09uKwyt8CS16/Oi4KQeVcZpSF+YnMXJaEWA+qBfoaUhcjRk+VF+a4kQIpPX1Lpw/M3pWsQJtZayIUriM8WgDwGdU88jGDdvbHN+YLXgaboirhVdy/IaTupKk2Tug= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776873045; c=relaxed/simple; bh=FpsxQZvjVjd9Akt2HBKxJZNBDYIwr4Pi2TKkjE5Tlz4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qJ/1DMz25IAPxFkiHaual8HJ6MynL2jZ0AGjx4o+4EAcgM4UwaSL/tFKK4L9AkL10FnjrTvRByETPuKHj04LaqwXk8ed6iNBatDirAJ3iglI/a/wfLPSXjkCRVKWMbGOpEkaWCp+z0tgGqyMnLyUMgUFDX83ZFwdUMaccqtxmIo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=enPaOMzz; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="enPaOMzz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E0CABC2BCB4; Wed, 22 Apr 2026 15:50:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776873045; bh=FpsxQZvjVjd9Akt2HBKxJZNBDYIwr4Pi2TKkjE5Tlz4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=enPaOMzziCmx6sr2LApjufNywy31WK/vha4S3YkkiF/0etI/sirJrRIEOLwClzd1H O2v51rMmm402y+uRLj8NnGOHQP8WC8l4f4RC913duPj3OS6gbQOEN5OAeIY8LEHr2f fUOx/MPLQdppyJqTQmNX2qLAfqJ6Kpb2sZQyYdi6/IvuUnuTeEM3pJp0XJSBRbfZTP O9+03Xys4uAEOU3bs24NB63O+tX0bvzm4dty3AmY8tjUo1UywPR3ml77bSbN6kUQOa 11CtWaLhvKLrfAzVhEFwhfYCOeKgEK0Xg90Xr32wBioPtJTl56QUBDa/jlgLX98vFE kr+BqycHO6Ehg== Message-ID: <924eb446-10b3-4167-84ff-289efed03388@kernel.org> Date: Wed, 22 Apr 2026 17:50:39 +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: [BUG] WARNING in workingset_activation triggered by KVM page fault path on Linux 7.0.0-08391-g1d51b370a0f8 To: Sean Christopherson Cc: Zw Tang , "linux-mm@kvack.org" , "akpm@linux-foundation.org" , "hannes@cmpxchg.org" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "pbonzini@redhat.com" References: <177d0a41-5267-41f3-bc77-415b756ea4bb@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/22/26 15:01, Sean Christopherson wrote: > On Wed, Apr 22, 2026, David Hildenbrand (Arm) wrote: >> On 4/22/26 04:06, Zw Tang wrote: >>> Hi David, >>> >>> Thanks for pointing this out. >>> >>> You are right. The commit id I sent was incorrect. I mistakenly used the >>> git describe-style suffix g1d51b370a0f8, but the actual git commit is: >>> >>> 1d51b370a0f8f642f4fc84c795fbedac0fcdbbd2 >>> >>> The short commit id is: >>> >>> 1d51b370a0f8 >>> >>> Sorry for the confusion. >>> >>> I am also re-checking whether the kernel image was built from a clean tree >>> and whether there were any local modifications when the crash was reproduced, >>> so that the reported source line numbers match the exact build. >> >> Okay, on that tree include/linux/memcontrol.h:381 points at >> >> lockdep_assert_once(rcu_read_lock_held() || >> lockdep_is_held(&cgroup_mutex)); >> >> lockdep_is_held() would not trigger a warning like that IIRC, but >> >> lockdep_assert_once() does >> >> do { WARN_ON_ONCE(debug_locks && !(cond)); } while (0) >> >> >> So likely we are calling obj_cgroup_memcg() without the RCU read lock held? >> >> >> kvm_release_page_clean()->kvm_set_page_accessed()->mark_page_accessed()->folio_mark_accessed()->workingset_activation() >> >> ... grabs the RCU lock, though, before calling >> >> rcu_read_lock(); >> workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio)); >> rcu_read_unlock(); > > No? Since commit 906c38ff52e9 ("memcg: workingset: remove folio_memcg_rcu usage"), > I see: Yeah, I used git show show 1d51b370a0f8f642f4fc84c795fbedac0fcdbbd2:include/linux/memcontrol.h to look at the file but then explored the other code without a checkout, ugh. > > void workingset_activation(struct folio *folio) > { > /* > * Filter non-memcg pages here, e.g. unmap can call > * mark_page_accessed() on VDSO pages. > */ > if (mem_cgroup_disabled() || folio_memcg_charged(folio)) > workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio)); > } > > But for the life of me, I can't figure out how obj_cgroup_memcg() is being reached, > and I haven't been able to reproduce the splat to add instrumentation (though I > haven't tried very hard). folio_lruvec() does a folio_memcg(folio) that does a obj_cgroup_memcg() for folio_memcg_kmem(). So the page was charged through __memcg_kmem_charge_page() by passing __GFP_ACCOUNT to the kernel. So this is likely not some ordinary folio? -- Cheers, David