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[80.187.80.144]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e693c9828sm21809955e9.20.2025.10.02.00.22.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Oct 2025 00:22:48 -0700 (PDT) Message-ID: <4909d194-58b7-4e94-b730-f916100238d3@redhat.com> Date: Thu, 2 Oct 2025 09:22:45 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm: always call rmap_walk() on locked folios To: Lokesh Gidra , Dan Williams , Alistair Popple Cc: akpm@linux-foundation.org, linux-mm@kvack.org, kaleshsingh@google.com, ngeoffray@google.com, jannh@google.com, Lorenzo Stoakes , Harry Yoo , Peter Xu , Suren Baghdasaryan , Barry Song , SeongJae Park References: <20250918055135.2881413-1-lokeshgidra@google.com> <20250918055135.2881413-2-lokeshgidra@google.com> <2c9df5ee-6109-4fa5-b895-ad8e47d34bee@redhat.com> <5549ac3a-20cf-4959-ac53-0a89ed0eadd2@redhat.com> <7305f905-0f81-4268-a3b3-933ac00cdb6a@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 6E4DB140005 X-Stat-Signature: rhm8fj9p9gnp9jryoyu9pyw7gfswmyw3 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1759389774-335431 X-HE-Meta: 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 zeFMNjPd CuAtdltIzVm6eZuGUAkNfLCciZUVCd4JRXrUOirvioh+n2qOvpAFthNosbo2UuRV2DtrJI5BiXQ9gOYkAS1W1m2Zn0O/g2HennSRYn5VwBYrSHWdrb86KSh3MR7B4lNJH7Tv4D2flBuJ5nV818URZzdtEP/VC8mvCVXy/dcLIck3RRo/xYSnZ5dImZXdil2bIQsZ+qnc4wptUSTfiygOVQyvFDHesGqGwPmDxpCbS3mPwJRmEXi80GJvq4qPYFdfcaNyliMGz6Wk6bSbaFAu6AYxIjMRkjBPgo9VnauhCcQhxCwGtur529DUdaqFEu8LZ9p2xqwkPjzM1wyXjxRZy/BE0xlYp9CfPXVC+NkRTGSIvPWxy8rWSnQZphFVzpSt6IRxsIYoyfWJEFw8t01a8z1AIAAbp1F2sjMwI9Aff8t1mGQT3684lggj2IjNHJb1EmiV98/EvawETQfnT4Ka51Trwq72sGhaol5at X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 02.10.25 08:46, Lokesh Gidra wrote: > On Thu, Sep 25, 2025 at 4:07 AM David Hildenbrand wrote: >> >> On 24.09.25 21:17, Lokesh Gidra wrote: >>> On Wed, Sep 24, 2025 at 3:00 AM David Hildenbrand wrote: >>>> >>>>>> >>>>>> Is mf_generic_kill_procs()->collect_procs() problematic? >>>>>> >>>>>> The dax_lock_folio/dax_unlock_folio part confuses me: I think it only >>>>>> locks an entry in the page cache but not the actual folio ("Lock the DAX >>>>>> entry corresponding to a folio")? >>>>> Yeah. The name dax_lock_folio() gives an impression as if the folio is >>>>> locked but it isn't :) >>>> >>>> Sorry for the late reply, I saw you posted v2 in the meantime. >>>> >>>>> >>>>> IIUC, a dax folio can't have an anon_vma (folio->mapping is actually >>>>> an address_space instead of anon_vma), right? >>>> >>>> We have these weird device-private dax folios that are anonymous and >>>> should have the anon_vma set up. >>>> >>>>> So, I thought it wasn't >>>>> required to actually lock the folio in this case. Please let me know >>>>> if you want me to still lock the folio around collect_procs(), or add >>>>> a comment? >>>> >>>> I think we can end up reaching memory_failure_dev_pagemap() with an >>>> anonymous dax folio. >>>> >>>> Not sure if anything would prevent us into calling >>>> >>>> mf_generic_kill_procs()->collect_procs()->collect_procs_anon()->folio_lock_anon_vma_read() >>>> >>> I must be missing something but dax_lock_folio() dereferences >> >> Maybe the code is missing something :) >> >>> folio->mapping (to get to host) without checking for >>> FOLIO_MAPPING_FLAGS presence. If it were an anon folio, wouldn't that >>> be a problem? And then in collect_procs() we obviously check for >>> folio_test_anon() on the same folio before calling >>> collect_procs_anon(). >> >> Right, if we reach dax_lock_folio() with an anon folio we are probably >> already messing things up? Not sure if the "!dax_mapping(mapping)" would >> save us, likely not, because it would be an anon_vma. >> >> Hopefully Dan+Alistair have a clue how this works and if it already >> works as expected with device-private anon folios. >> > Hi David, > > Any suggestion how to make progress? Should I upload v3 with > mf_generic_kill_procs()->collect_procs() in folio-lock critical > section? Staring at mf_generic_kill_procs() once again, we have this switch (pgmap->type) { case MEMORY_DEVICE_PRIVATE: case MEMORY_DEVICE_COHERENT: rc = -ENXIO; goto unlock; ... } IIRC, all anon device folios are MEMORY_DEVICE_PRIVATE, so we should actually not succeed in this function and just abort. We still call dax_lock_folio() earlier, which likely doesn't do the right thing for anon device folios, but that's an existing issue. So regarding your patch I think we're good! -- Cheers David / dhildenb