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AFNElJ9QvX91dUezn6vU8xu2qsQVfRqoSQuMDLNXZ3ewWmnGSzBsWedBQGD8jnYmnpfZAXLrbnUTsFsakQ==@kvack.org X-Gm-Message-State: AOJu0Yyy8y61ivFAB/NdQyy0fQ1DRfnaNNgNz2lOm6oFtDZ42IvQfTWT X+C70G+hh4NK9gRlxlFykp6PqZKAa8rAj42pMbk2lrgPLEReNKmHmi7gOxWZqbGTA/sDWbqzS+T Xl9AjFQ== X-Received: from plsp12.prod.google.com ([2002:a17:902:bd0c:b0:2b2:4270:9f7c]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:3dad:b0:2b4:5dff:310f with SMTP id d9443c01a7336-2b5f9fcf868mr138652695ad.34.1776862911351; Wed, 22 Apr 2026 06:01:51 -0700 (PDT) Date: Wed, 22 Apr 2026 06:01:44 -0700 In-Reply-To: <177d0a41-5267-41f3-bc77-415b756ea4bb@kernel.org> Mime-Version: 1.0 References: <177d0a41-5267-41f3-bc77-415b756ea4bb@kernel.org> Message-ID: Subject: Re: [BUG] WARNING in workingset_activation triggered by KVM page fault path on Linux 7.0.0-08391-g1d51b370a0f8 From: Sean Christopherson To: "David Hildenbrand (Arm)" 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" Content-Type: text/plain; charset="us-ascii" X-Stat-Signature: n9bm5agngnrmuxjuxee1wjbwzmxxgs97 X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 0B1591A0018 X-HE-Tag: 1776862912-586716 X-HE-Meta: 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 RB9DX6Ko 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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: 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). > The folio_memcg_charged() only checks folio->memcg_data. > > So something does not quite add up here? > > -- > Cheers, > > David