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SubjectRe: [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@suse.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@suse.de>
> Reviewed-by: Rik van Riel <riel@redhat.com>
> Cc: Alex Thorlton <athorlton@sgi.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
>
> 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 <errno.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <sys/mman.h>
>
> 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).

Odds are this also shows up in 3.13, right?

thanks,

greg k-h


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