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[2003:cb:c703:7600:a8ea:29ce:7ee3:dd41]) by smtp.gmail.com with ESMTPSA id m21-20020a05600c4f5500b003b4fe03c881sm6809659wmq.48.2022.11.30.08.18.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Nov 2022 08:18:46 -0800 (PST) Message-ID: <65a3a912-3534-6718-2c55-e0d4b5246f1e@redhat.com> Date: Wed, 30 Nov 2022 17:18:45 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.5.0 To: Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: James Houghton , Jann Horn , Andrew Morton , Andrea Arcangeli , Rik van Riel , Nadav Amit , Miaohe Lin , Muchun Song , Mike Kravetz References: <20221129193526.3588187-1-peterx@redhat.com> <20221129193526.3588187-10-peterx@redhat.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH 09/10] mm/hugetlb: Make page_vma_mapped_walk() safe to pmd unshare In-Reply-To: <20221129193526.3588187-10-peterx@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1669825130; a=rsa-sha256; cv=none; b=3ipRiJSOmxON2XEgfwLxWa70e0f+umi9/NhgVbaq9Yau6MOHawcBOYhUudCcQdiLlboXww R9BhSH9HQ10BrTBEMTQcVWotr84QelRghwJJEiAwUMmVBwtRZEu53dDGiT8UiAoRAYONbn rWVGV4mZwL57soy/PM76Otkd+xDSqnw= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=OUeoVNtO; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf04.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1669825130; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=cnZGBkwWgbFX167qaVZmI9S2d5cNmBBPcO+crFwoMks=; b=iSX8YL9i2VLF4RT+Ey7ASXX++jdMCwDiawAyRAuis14yCafPw8FqFwYbfSlKmTLEZA30K5 3K9wTlieXrt5mIUhYPeqXSOCr5cqMDtZQjG8RO1P/I/5piUrNCar+8h3K9Z9iBoF7raUJy 2KPP1oWN9zV1MDNCqG4HtSGW8YFk5CM= X-Rspamd-Queue-Id: 0056E4000D Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=OUeoVNtO; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf04.hostedemail.com: domain of david@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=david@redhat.com X-Rspamd-Server: rspam12 X-Rspam-User: X-Stat-Signature: ik61mdo9a1fdd9pqu4qn4n33skq3c43o X-HE-Tag: 1669825129-89567 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: On 29.11.22 20:35, Peter Xu wrote: > Since page_vma_mapped_walk() walks the pgtable, it needs the vma lock > to make sure the pgtable page will not be freed concurrently. > > Signed-off-by: Peter Xu > --- > include/linux/rmap.h | 4 ++++ > mm/page_vma_mapped.c | 5 ++++- > 2 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/include/linux/rmap.h b/include/linux/rmap.h > index bd3504d11b15..a50d18bb86aa 100644 > --- a/include/linux/rmap.h > +++ b/include/linux/rmap.h > @@ -13,6 +13,7 @@ > #include > #include > #include > +#include > > /* > * The anon_vma heads a list of private "related" vmas, to scan if > @@ -408,6 +409,9 @@ static inline void page_vma_mapped_walk_done(struct page_vma_mapped_walk *pvmw) > pte_unmap(pvmw->pte); > if (pvmw->ptl) > spin_unlock(pvmw->ptl); > + /* This needs to be after unlock of the spinlock */ > + if (is_vm_hugetlb_page(pvmw->vma)) > + hugetlb_vma_unlock_read(pvmw->vma); > } > > bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw); > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > index 93e13fc17d3c..f94ec78b54ff 100644 > --- a/mm/page_vma_mapped.c > +++ b/mm/page_vma_mapped.c > @@ -169,10 +169,13 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > if (pvmw->pte) > return not_found(pvmw); > > + hugetlb_vma_lock_read(vma); > /* when pud is not present, pte will be NULL */ > pvmw->pte = huge_pte_offset(mm, pvmw->address, size); > - if (!pvmw->pte) > + if (!pvmw->pte) { > + hugetlb_vma_unlock_read(vma); > return false; > + } > > pvmw->ptl = huge_pte_lock(hstate, mm, pvmw->pte); > if (!check_pte(pvmw)) Looking at code like mm/damon/paddr.c:__damon_pa_mkold() and reading the doc of page_vma_mapped_walk(), this might be broken. Can't we get page_vma_mapped_walk() called multiple times? Wouldn't we have to remember that we already took the lock to not lock twice, and to see if we really have to unlock in page_vma_mapped_walk_done() ? -- Thanks, David / dhildenb