From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AIpwx48+xcVTCuz/yhzky/IId2rr0Pbdx+0zOkSwQPLdLPu+7LXRPk3LuIudGc7eoVvc5lKCb/5A ARC-Seal: i=1; a=rsa-sha256; t=1522168287; cv=none; d=google.com; s=arc-20160816; b=aRqVWjQeCis6En1fob9dKXVwgqNoRzDfpclqUJkrQm8MK+BAR2bOVVU5bdMld1xPfU VWIJiX4/IFA5Ajgwwbv3hOMhQrjO2m9m6HG9FPYY/aXTnPd8R97fXe5UDLzKA7LK6Qjd Y6UOgj77jSWcb0RG4UIjoyCUrMHJFF4YWlhO5hoqS3deOdHR7nZlYaSvfDOXe2uZr+yr Cy0LGd5T2ZNQ977tslh3T8dV4LoMJKYQ22ohPSGfSlAEAC7SnpPDJ+mf7LaiYTzOdnd+ D0a8NLsVOPRvAMRIBa6gznOZ/iKcnMNZ8CN4kfd60mk+gmarE/+S4fr2gbs9VdFUxx9K j1qw== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:user-agent:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=szdFIIAPTHsoGMIfcOCasvH1pBfu+QUJMST0B1mHOms=; b=rzn1yWoQ8CrZCBlzx1L59xNiRI20JGYxTHQRoipYh5Bx8u1WYZ8MzOmEyZHFohPO6/ /LgO4xcS/0H7jAJP048Vrm/1sABwO1bz/5JYtkMsikL8j0/ceeQr7NAgVrS3q6z/7Der FrffmtqrjtfKyJpIIrN5earZWD6aVhrWWmQcKBWOrCV0Np30cLafWNf0zzcyF8KyGjtM 13J77RuP1OHIv46OwMCWTJIHhAe+gYG3tZjCmRqzFEdyX+iplW6F1pKxtOc+ZxO3mB6t ZDzwD8SISP5nUWkhd+FXYXKxvxDfC/64rM8xv4yR7dPxuq+V/hU7ERWmvNzKKz6XclMn X+9w== ARC-Authentication-Results: i=1; mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.61.202 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.61.202 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Kirill A. Shutemov" , Laura Abbott , Jerome Marchand , Vlastimil Babka , Andrew Morton , Linus Torvalds Subject: [PATCH 4.9 26/67] mm/khugepaged.c: convert VM_BUG_ON() to collapse fail Date: Tue, 27 Mar 2018 18:27:18 +0200 Message-Id: <20180327162728.359297909@linuxfoundation.org> X-Mailer: git-send-email 2.16.3 In-Reply-To: <20180327162726.702411083@linuxfoundation.org> References: <20180327162726.702411083@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-LABELS: =?utf-8?b?IlxcU2VudCI=?= X-GMAIL-THRID: =?utf-8?q?1596109134052943557?= X-GMAIL-MSGID: =?utf-8?q?1596109134052943557?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kirill A. Shutemov commit fece2029a9e65b9a990831afe2a2b83290cbbe26 upstream. khugepaged is not yet able to convert PTE-mapped huge pages back to PMD mapped. We do not collapse such pages. See check khugepaged_scan_pmd(). But if between khugepaged_scan_pmd() and __collapse_huge_page_isolate() somebody managed to instantiate THP in the range and then split the PMD back to PTEs we would have a problem -- VM_BUG_ON_PAGE(PageCompound(page)) will get triggered. It's possible since we drop mmap_sem during collapse to re-take for write. Replace the VM_BUG_ON() with graceful collapse fail. Link: http://lkml.kernel.org/r/20180315152353.27989-1-kirill.shutemov@linux.intel.com Fixes: b1caa957ae6d ("khugepaged: ignore pmd tables with THP mapped with ptes") Signed-off-by: Kirill A. Shutemov Cc: Laura Abbott Cc: Jerome Marchand Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/khugepaged.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -528,7 +528,12 @@ static int __collapse_huge_page_isolate( goto out; } - VM_BUG_ON_PAGE(PageCompound(page), page); + /* TODO: teach khugepaged to collapse THP mapped with pte */ + if (PageCompound(page)) { + result = SCAN_PAGE_COMPOUND; + goto out; + } + VM_BUG_ON_PAGE(!PageAnon(page), page); VM_BUG_ON_PAGE(!PageSwapBacked(page), page);