From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ee0-f42.google.com (mail-ee0-f42.google.com [74.125.83.42]) by kanga.kvack.org (Postfix) with ESMTP id 6F4856B0031 for ; Sun, 12 Jan 2014 06:34:02 -0500 (EST) Received: by mail-ee0-f42.google.com with SMTP id e49so941611eek.15 for ; Sun, 12 Jan 2014 03:34:01 -0800 (PST) Received: from jenni2.inet.fi (mta-out.inet.fi. [195.156.147.13]) by mx.google.com with ESMTP id a9si22055152eew.222.2014.01.12.03.34.00 for ; Sun, 12 Jan 2014 03:34:00 -0800 (PST) Date: Sun, 12 Jan 2014 13:33:53 +0200 From: "Kirill A. Shutemov" Subject: Re: [PATCH] thp: fix copy_page_rep GPF by testing is_huge_zero_pmd once only Message-ID: <20140112113353.GA21893@node.dhcp.inet.fi> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Linus Torvalds , Andrew Morton , "Kirill A. Shutemov" , Sasha Levin , Mel Gorman , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Sun, Jan 12, 2014 at 01:25:21AM -0800, Hugh Dickins wrote: > We see General Protection Fault on RSI in copy_page_rep: > that RSI is what you get from a NULL struct page pointer. > > RIP: 0010:[] [] copy_page_rep+0x5/0x10 > RSP: 0000:ffff880136e15c00 EFLAGS: 00010286 > RAX: ffff880000000000 RBX: ffff880136e14000 RCX: 0000000000000200 > RDX: 6db6db6db6db6db7 RSI: db73880000000000 RDI: ffff880dd0c00000 > RBP: ffff880136e15c18 R08: 0000000000000200 R09: 000000000005987c > R10: 000000000005987c R11: 0000000000000200 R12: 0000000000000001 > R13: ffffea00305aa000 R14: 0000000000000000 R15: 0000000000000000 > FS: 00007f195752f700(0000) GS:ffff880c7fc20000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000093010000 CR3: 00000001458e1000 CR4: 00000000000027e0 > Call Trace: > [] ? copy_user_highpage.isra.43+0x65/0x80 > [] copy_user_huge_page+0x93/0xab > [] do_huge_pmd_wp_page+0x710/0x815 > [] handle_mm_fault+0x15d8/0x1d70 > [] __do_page_fault+0x14d/0x840 > [] ? SYSC_recvfrom+0x10d/0x210 > [] do_page_fault+0x2f/0x90 > [] page_fault+0x22/0x30 > > do_huge_pmd_wp_page() tests is_huge_zero_pmd(orig_pmd) four times: > but since shrink_huge_zero_page() can free the huge_zero_page, and > we have no hold of our own on it here (except where the fourth test > holds page_table_lock and has checked pmd_same), it's possible for > it to answer yes the first time, but no to the second or third test. > Change all those last three to tests for NULL page. > > (Note: this is not the same issue as trinity's DEBUG_PAGEALLOC BUG > in copy_page_rep with RSI: ffff88009c422000, reported by Sasha Levin > in https://lkml.org/lkml/2013/3/29/103. I believe that one is due > to the source page being split, and a tail page freed, while copy > is in progress; and not a problem without DEBUG_PAGEALLOC, since > the pmd_same check will prevent a miscopy from being made visible.) > > Fixes: 97ae17497e99 ("thp: implement refcounting for huge zero page") > Signed-off-by: Hugh Dickins > Cc: stable@vger.kernel.org # v3.10 v3.11 v3.12 Reviewed-by: Kirill A. Shutemov -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org