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Message-ID: <20140123170337.GM4963@suse.de> Date: Thu, 23 Jan 2014 17:03:37 +0000 From: Mel Gorman <mgorman@...e.de> To: Steven Noonan <steven@...inklabs.net> Cc: Linux Kernel mailing List <linux-kernel@...r.kernel.org>, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, Rik van Riel <riel@...hat.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Alex Thorlton <athorlton@....com>, Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org> Subject: Re: [BISECTED] Linux 3.12.7 introduces page map handling regression On Tue, Jan 21, 2014 at 03:27:08PM -0800, Steven Noonan wrote: > 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] [<ffffffff814c763b>] dump_stack+0x45/0x56 > [ 60.654928] [<ffffffff8116784e>] print_bad_pte+0x22e/0x250 > [ 60.654933] [<ffffffff81169073>] unmap_single_vma+0x583/0x890 > [ 60.654938] [<ffffffff8116a405>] unmap_vmas+0x65/0x90 > [ 60.654942] [<ffffffff81173795>] exit_mmap+0xc5/0x170 > [ 60.654948] [<ffffffff8105d295>] mmput+0x65/0x100 > [ 60.654952] [<ffffffff81062983>] do_exit+0x393/0x9e0 > [ 60.654955] [<ffffffff810630dc>] do_group_exit+0xcc/0x140 > [ 60.654959] [<ffffffff81063164>] SyS_exit_group+0x14/0x20 > [ 60.654965] [<ffffffff814d602d>] 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 <mgorman@...e.de> > 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 <mgorman@...e.de> > Reviewed-by: Rik van Riel <riel@...hat.com> > Cc: Alex Thorlton <athorlton@....com> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org> > Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> > Sorry for the long delay in responding. I've only managed to get as far as this mail now and it's already my evening and I won't be able to work on it now either. Based on the patch a possible explanation is that I called the page table mknonnuma helpers on a non-numa PTE and there is now a mixup between the _PAGE_PRESENT and _PAGE_PROTNONE bits. It feels like a bad fit though and would not explain why it only affects Xen. A slightly better fit would be if the page table helpers for numa hinting flags are colliding badly with the paravirt interface somehow. A git grep for _PAGE_PROTNONE on xen showed up nothing but _PAGE_PRESENT has special meaning and that might be what I trashed. -- Mel Gorman SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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