Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754300AbaAUX1T (ORCPT ); Tue, 21 Jan 2014 18:27:19 -0500 Received: from mail-pd0-f177.google.com ([209.85.192.177]:64999 "EHLO mail-pd0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751873AbaAUX1Q (ORCPT ); Tue, 21 Jan 2014 18:27:16 -0500 Date: Tue, 21 Jan 2014 15:27:08 -0800 From: Steven Noonan To: Linux Kernel mailing List Cc: Konrad Rzeszutek Wilk , Mel Gorman , Rik van Riel , Greg Kroah-Hartman , Alex Thorlton , Andrew Morton , Linus Torvalds Subject: [BISECTED] Linux 3.12.7 introduces page map handling regression Message-ID: <20140121232708.GA29787@amazon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A user reported a problem starting vsftpd on a Xen paravirtualized guest, with this in dmesg: [ 60.654862] BUG: Bad page map in process vsftpd pte:8000000493b88165 pmd:e9cc01067 [ 60.654876] page:ffffea00124ee200 count:0 mapcount:-1 mapping: (null) index:0x0 [ 60.654879] page flags: 0x2ffc0000000014(referenced|dirty) [ 60.654885] addr:00007f97eea74000 vm_flags:00100071 anon_vma:ffff880e98f80380 mapping: (null) index:7f97eea74 [ 60.654890] CPU: 4 PID: 587 Comm: vsftpd Not tainted 3.12.7-1-ec2 #1 [ 60.654893] ffff880e9cc6ec38 ffff880e9cc61ca0 ffffffff814c763b 00007f97eea74000 [ 60.654900] ffff880e9cc61ce8 ffffffff8116784e 0000000000000000 0000000000000000 [ 60.654906] ffff880e9cc013a0 ffffea00124ee200 00007f97eea75000 ffff880e9cc61e10 [ 60.654912] Call Trace: [ 60.654921] [] dump_stack+0x45/0x56 [ 60.654928] [] print_bad_pte+0x22e/0x250 [ 60.654933] [] unmap_single_vma+0x583/0x890 [ 60.654938] [] unmap_vmas+0x65/0x90 [ 60.654942] [] exit_mmap+0xc5/0x170 [ 60.654948] [] mmput+0x65/0x100 [ 60.654952] [] do_exit+0x393/0x9e0 [ 60.654955] [] do_group_exit+0xcc/0x140 [ 60.654959] [] SyS_exit_group+0x14/0x20 [ 60.654965] [] system_call_fastpath+0x1a/0x1f [ 60.654968] Disabling lock debugging due to kernel taint [ 60.655191] BUG: Bad rss-counter state mm:ffff880e9ca60580 idx:0 val:-1 [ 60.655196] BUG: Bad rss-counter state mm:ffff880e9ca60580 idx:1 val:1 The issue could not be reproduced under an HVM instance with the same kernel, so it appears to be exclusive to paravirtual Xen guests. I noted that it wasn't present in 3.10.27, but was present in 3.12.7 and 3.12.8. I ran through a bisection to find the root cause: # start: 'v3.12.7' 'v3.10.27' # bad: [4301b7a8] Linux 3.12.7 # good: [1071ea6e] Linux 3.10.27 # good: [8bb495e3] Linux 3.10 # good: [8fe73691] staging: comedi: comedi_bond: change return value # good: [22e04f6b] Merge branch 'for-linus' of git://git.kernel.org/p # good: [b7c09ad4] Merge branch 'for-linus' of git://git.kernel.org/p # good: [13caa8ed] Merge git://git.kernel.org/pub/scm/linux/kernel/gi # good: [13caa8ed] Merge git://git.kernel.org/pub/scm/linux/kernel/gi # good: [f5fa9283] ipv6: reset dst.expires value when clearing expire # good: [4af9d888] bridge: flush br's address entry in fdb when remov # good: [8c13daf6] dm delay: fix a possible deadlock due to shared wo # good: [93c02d70] firewire: sbp2: bring back WRITE SAME support # good: [18065245] ACPI / PCI / hotplug: Avoid warning when _ADR not # bad: [8807a436] mm/memory-failure.c: transfer page count from head # bad: [fd5df800] mm: numa: avoid unnecessary disruption of NUMA hin # good: [c18e3316] mm: numa: do not clear PMD during PTE update scan # good: [f3b578d9] mm: numa: avoid unnecessary work on the failure pa # bad: [3d792d61] mm: numa: clear numa hinting information on mprote # good: [cefeb279] sched: numa: skip inaccessible VMAs # first bad: [3d792d61] mm: numa: clear numa hinting information on mprote If only I'd tested v3.12.0, that bisection would have been a lot shorter! It looks like this is the change implicated (introduced in v3.12.7): commit 3d792d616ba408ab55a54c1bb75a9367d997acfa Author: Mel Gorman Date: Tue Jan 7 14:00:44 2014 +0000 mm: numa: clear numa hinting information on mprotect commit 1667918b6483b12a6496bf54151b827b8235d7b1 upstream. On a protection change it is no longer clear if the page should be still accessible. This patch clears the NUMA hinting fault bits on a protection change. Signed-off-by: Mel Gorman Reviewed-by: Rik van Riel Cc: Alex Thorlton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman This clearly points to breakage of mprotect() in particular. Checking what vsftpd was doing via strace, I was able to come up with a simple test case which triggers the issue: #include #include #include #include void die(const char *what) { perror(what); exit(1); } int main(int arg, char **argv) { void *p = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (p == MAP_FAILED) die("mmap"); /* Tickle the page. */ ((char *)p)[0] = 0; if (mprotect(p, 4096, PROT_NONE) != 0) die("mprotect"); if (mprotect(p, 4096, PROT_READ) != 0) die("mprotect"); if (munmap(p, 4096) != 0) die("munmap"); return 0; } This could probably be reduced further. I didn't spend much time on it. Adding people cited in the patch to CC, as well as Konrad since this is a Xen issue (I haven't been able to repro on HVM or bare metal so far). Any ideas what's causing the BUG, and how we can fix it? - Steven -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/