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Shutemov" , Matthew Wilcox , Andrew Morton , Linux MM , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1654819314; a=rsa-sha256; cv=none; b=n4O0icuNG/UtEXW1xZahdGBdvB5PD4ZbiinLKV6CUgtgKZSB6DDkqZ2dvhR2VUCdCc5IqB pkf6KU/zwUjnCf7CFgRzJdAEllU9gs0ri8D0H2Q2y/L1KPIr9apgDsiTZEv2ETjRmd0CPC NDPkxGxvWG4Q6XhqNGr4/Ftnv1FKcC0= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=gKODhx7X; spf=pass (imf02.hostedemail.com: domain of shy828301@gmail.com designates 209.85.210.178 as permitted sender) smtp.mailfrom=shy828301@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1654819314; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=1O6AEKHlVD9Bngjug6xvCzo7n1uYfU+pNTujv/UlryM=; b=8Bt8VHR3FVpeRfCYiz4h0fyJ6B4dE8CUF+/T6+sJb0L7tJ5O97w2GLStEM0vZZWcEjr167 20QmOwvTRsHvYC7d9tr10gu+RMVCL0zEpfBo4TpESxEM/wn9RSv2fmy/f6jbds3JpJF1Uv +AZmZVAvZboYn8/K+IACYoBDjdCAPo8= X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: E104680085 X-Stat-Signature: a18f39kmsy9j7degi8mjoa6k91yko46k X-Rspam-User: Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=gKODhx7X; spf=pass (imf02.hostedemail.com: domain of shy828301@gmail.com designates 209.85.210.178 as permitted sender) smtp.mailfrom=shy828301@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-HE-Tag: 1654819313-612551 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 Thu, Jun 9, 2022 at 4:24 PM Zach O'Keefe wrote: > > On Mon, Jun 6, 2022 at 2:44 PM Yang Shi wrote: > > > > The hugepage_vma_check() already checked it, so remove the redundant > > check. > > > > Signed-off-by: Yang Shi > > --- > > mm/khugepaged.c | 3 --- > > 1 file changed, 3 deletions(-) > > > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > > index d0f8020164fc..7a5d1c1a1833 100644 > > --- a/mm/khugepaged.c > > +++ b/mm/khugepaged.c > > @@ -966,9 +966,6 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address, > > return SCAN_ADDRESS_RANGE; > > if (!hugepage_vma_check(vma, vma->vm_flags)) > > return SCAN_VMA_CHECK; > > - /* Anon VMA expected */ > > - if (!vma->anon_vma || !vma_is_anonymous(vma)) > > - return SCAN_VMA_CHECK; > > return 0; > > } > > > > -- > > 2.26.3 > > > > > > So, I don't know if this is possible, but I wonder if there is a race here: > > hugepage_vma_revalidate() is called in the anon path when mmap_lock > after dropped + reacquired, and we want to refind / revalidate the > vma, since it might have changed. > > There is the possibility that the memory was unmapped, then remapped > as file or shmem. If so, hugepage_vma_check() could return true > without actually checking vma->anon_vma || !vma_is_anonymous(vma) - > and we probably do want to (re)validate that this is indeed still an > anon vma. Nice catch! Totally possible. I did overlook this. I will drop this patch in the next version or maybe making the comment clearer is a better choice.