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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776160271; bh=50boV389vtA1+fAhY6j7k57/eNUILSasLReQVNKDYe4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=nRrQy0Mme0Zu5CmHdzP0kUS4hRX/b17AcEx5OY8UEXG+t6/Lv/c5bBDJCjZ3XOutK WUGiIJJZ9rEgXUikzo18NL0l4sqDdvC4iHxGFC+LILjeFo6+SGbnn29Gwbd8VCVlDL zjmWudHYcVd0j2qG9oi82PfgptpnLdO5ek6Jf4qvdTZOC++n0SVHLzNAetbhaws2pb DE7V1nzK+8FJjhHH03Qxjoo4TFWGxPTOE4ieYMvcBHZ06A1J7iAJuVejSGioFSCPA5 3D4jbnpPvh7Jq/PSVB1wHKknH0V4Qnc+KNM/P1Tj37q1RGAZpXaQxnSLCcv/SUG4a2 QnXLODj/wCIfg== Message-ID: <5914d296-934a-4662-b1cf-d0f23757df5b@kernel.org> Date: Tue, 14 Apr 2026 11:51:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate_device: fix double unlock and remove dead code To: Zi Yan Cc: Sunny Patel , Andrew Morton , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Balbir Singh References: <20260413130927.13263-1-nueralspacetech@gmail.com> <7579105a-1261-45db-90ba-5e660d202b80@kernel.org> <6073CBA5-2762-4FE4-98F5-27BC92482531@nvidia.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E5050180005 X-Stat-Signature: otiojjdcrtb4r4z573bjez1brybuwdrr X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1776160271-6227 X-HE-Meta: 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 y0BJd8HW dEmhpYukwAetCI/PnpkL+qRYBjWxm5yn0yteqUb8AaFIjUwrgmoVG/owT3YigTgqRUVRmaQS+1hiQLgWspJm1rAEAfQ1basOuCF/U5l4narjT0g+5EfHcDWf2bi05spcYUj3xx4PbRRVdBUaYrdNAuibwZ8SgAXERA2ire6yj6PGegYyL7DSXBta2uNKlM/B5RQxNHZlGIJoh5484Cc+KJr8IbRP9xGPuoN1uUd5fqKL0CEcGCkz5HB99jtpXqxqhEtsh8e7NgTZaGftfmyK5gbT4uw1YZy0H8SUpGi4bIip3Ua4HWwt+fuWS4j1EothYCEPdjoYZ3BWrTXIjXLdNX7ZbhrIDgAe5faJA4q0DTBhMhVo6s86UTxqIrgNCsdImVSKDw+OuvYmoza5gdQlvYdDqnQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/13/26 22:03, Zi Yan wrote: > On 13 Apr 2026, at 15:38, David Hildenbrand (Arm) wrote: > >> On 4/13/26 15:09, Sunny Patel wrote: >>> Fix two bugs in device migration paths: >>> >>> 1) migrate_vma_collect_huge_pmd() calls spin_unlock after >>> softleaf_entry_wait_on_locked(), which already releases the ptl. >>> >>> 2) migrate_vma_insert_huge_pmd_page() has a dead else-if branch and this >>> branch is always unreachable. >>> >> >> Can you move 1) into a separate patch, add a Fixes: tag an CC stable? >> >> I think it is >> >> Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone >> device pages") >> >> 2) will then be a pure cleanup patch. >> >> Thanks! >> >>> Signed-off-by: Sunny Patel >>> --- >>> mm/migrate_device.c | 4 +--- >>> 1 file changed, 1 insertion(+), 3 deletions(-) >>> >>> diff --git a/mm/migrate_device.c b/mm/migrate_device.c >>> index 8079676c8f1f..0e005c26ee88 100644 >>> --- a/mm/migrate_device.c >>> +++ b/mm/migrate_device.c >>> @@ -177,7 +177,6 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start, >>> >>> if (softleaf_is_migration(entry)) { >>> softleaf_entry_wait_on_locked(entry, ptl); >>> - spin_unlock(ptl); >> >> >> Yes, that looks correct to me. >> >>> return -EAGAIN; >>> } >>> >>> @@ -869,8 +868,7 @@ static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate, >>> if (!is_huge_zero_pmd(*pmdp)) >>> goto unlock_abort; >>> flush = true; >>> - } else if (!pmd_none(*pmdp)) >>> - goto unlock_abort; >>> + } >> >> Huh, how did that happen. I hope that it's not a typo and we wanted to >> check for something else. >> > > > Looking at the function and trying to figure this out, but find > VM_WARN_ON_FOLIO(!folio, folio) at the top, where folio is from page_folio(page). > It is either a nop or a zero dereferencing. It should be removed. Heh, VM_WARN_ON_FOLIO(!folio, folio) itself is completely odd. Dump NULL if NULL. Agreed that this should be removed. Or replaced by a VM_WARN_ON_ONCE(page); > > VM_WARN_ON_ONCE(!pmd_none(*pmdp) && !is_huge_zero_pmd(*pmdp)) can be removed > too, since the above ifs takes !pmd_none(*pmdp) && !is_huge_zero_pmd(*pmdp) > to unlock_abort. Right, and if that's an unexpected case, we should warn on that path instead. Like if (WARN_ON_ONCE(!is_huge_zero_pmd(*pmdp))) goto unlock_abort; > > Back to the above code: > > if (!pmd_none(*pmdp)) { > if (!is_huge_zero_pmd(*pmdp)) > goto unlock_abort; > flush = true; > } else if (!pmd_none(*pmdp)) > goto unlock_abort; > > It seems to me that the first if should be removed, since if pmdp is > not pmd_none(), others filled pmd entry before us, so no further > action should be taken, otherwise, the function will overwrite > some valid pmd entry. > > OK, look at migrate_vma_insert_page(), which does PTE level work, > the above code might be intended to do: > > if (pmd_present(*pmdp)) { > if (!is_huge_zero_pmd(*pmdp)) > goto unlock_abort; > flush = true; > } else if (!pmd_none(*pmdp)) > goto unlock_abort; Agreed, that makes more sense. Thanks! -- Cheers, David