A bug has been found by Will in the way pmds are set in THP.

The following patch fixes some problems Will experienced in LTP:
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-May/260476.html
This is in 3.15-rc8 as:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=ceb218359de22e70980801d4fa04fffbfc44adb8

I see this is already in LSK, has this fixed the issue?

Cheers,
--
Steve

On 27 May 2014 16:27, Mark Brown <email address hidden> wrote:
> That's in there. There's a few bits and pieces I'm still catching up on
> but the git branch is the standard LSK - git://git.linaro.org/kernel
> /linux-linaro-stable.git linux-linaro-lsk
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1320782
>
> Title:
>   LSK: BUG: failure at change_huge_pmd in huge_memory.c
>
> Status in Linaro Stable Kernel (LSK):
>   New
>
> Bug description:
>   While testing LTP test suite and memory stress tests the following bug
>   found.
>
>   Test case name: thp03
>
>   Error log:
>   --------------
>    thp02 0 TINFO : mremap 0x7f90e01000 to 0x7f8fa01000
>    thp02 1 TPASS : Still alive.
>    [ 2525.441528] BUG: failure at /home/buildslave/workspace/linux-linaro-stable-lsk-pre-merge/mm/huge_memory.c:1490/change_huge_pmd()!
>    [ 2525.455612] Kernel panic - not syncing: BUG!
>    [ 2525.459900] CPU: 5 PID: 5959 Comm: thp03 Not tainted 3.10.39+ #1
>    [ 2525.465924] Call trace:
>    [ 2525.468388] [<ffffffc000087464>] dump_backtrace+0x0/0x12c
>    [ 2525.473807] [<ffffffc0000875a0>] show_stack+0x10/0x1c
>    [ 2525.478879] [<ffffffc0005f36c4>] dump_stack+0x1c/0x28
>    [ 2525.483950] [<ffffffc0005ef0f4>] panic+0xe4/0x208
>    [ 2525.488673] [<ffffffc00016fffc>] change_huge_pmd+0xf0/0xf4
>    [ 2525.494178] [<ffffffc000156d7c>] change_protection+0x39c/0x49c
>    [ 2525.500031] [<ffffffc000156f5c>] mprotect_fixup+0xe0/0x204
>    [ 2525.505534] [<ffffffc000157180>] SyS_mprotect+0x100/0x210
>    [ 2525.510953] CPU0: stopping
>    [ 2525.513677] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.39+ #1
>    [ 2525.519787] Call trace:
>    [ 2525.522249] [<ffffffc000087464>] dump_backtrace+0x0/0x12c
>    [ 2525.527667] [<ffffffc0000875a0>] show_stack+0x10/0x1c
>    [ 2525.532737] [<ffffffc0005f36c4>] dump_stack+0x1c/0x28
>    [ 2525.537808] [<ffffffc00008dea0>] handle_IPI+0x15c/0x174
>    [ 2525.543050] [<ffffffc0000812cc>] gic_handle_irq+0x74/0x7c
>    [ 2525.548464] Exception stack(0xffffffc000827df0 to 0xffffffc000827f10)
>   ...
>   Complete Error log attached to this bug and same can be found in this link.
>   https://validation.linaro.org/scheduler/job/127011/log_file#L_27_9641
>
>   Bug reported kernel code snippet
>   -------------------------------------------------
>   File: mm/huge_memory.c
>
>   1479 int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
>   1480                 unsigned long addr, pgprot_t newprot, int prot_numa)
>   1481 {
>   1482         struct mm_struct *mm = vma->vm_mm;
>   1483         int ret = 0;
>   1484
>   1485         if (__pmd_trans_huge_lock(pmd, vma) == 1) {
>   1486                 pmd_t entry;
>   1487                 entry = pmdp_get_and_clear(mm, addr, pmd);
>   1488                 if (!prot_numa) {
>   1489                         entry = pmd_modify(entry, newprot);
>   1490                         BUG_ON(pmd_write(entry));
>
>   Test case description:
>   Test case link: http://people.linaro.org/~naresh.kamboju/ltp/testcases/kernel/mem/thp/thp03.c
>
>   /*
>    * thp03 - Case for spliting unaligned memory.
>    *       - System will panic if failed.
>    *
>    * Modified form a reproducer for
>    *          https://patchwork.kernel.org/patch/1358441/
>    * Kernel Commit id: 027ef6c87853b0a9df53175063028edb4950d476
>    * There was a bug in THP, will crash happened due to the following
>    * reason according to developers:
>    *
>    * most VM places are using pmd_none but a few are still using
>    * pmd_present. The meaning is about the same for the pmd. However
>    * pmd_present would return the wrong value on PROT_NONE ranges or in
>    * case of a non reproducible race with split_huge_page.
>    * When the code using pmd_present gets a false negative, the kernel will
>    * crash. It's just an annoying DoS with a BUG_ON triggering: no memory
>    * corruption and no data corruption (nor userland nor kernel).
>    */
>
>   Linux kernel version:
>   ---------------------
>   Linux version 3.10.39+ (buildslave@x86-64-07) (gcc version 4.8.3 20140203 (prerelease) (crosstool-NG linaro-1.13.1-4.8-2014.02 - Linaro GCC 2014.02) ) #1 SMP Fri May 16 08:37:37 UTC 2014
>   CPU: AArch64 Processor [410fd030] revision 0
>   Machine: Juno
>
>
>   Please let know if you need more information regarding this bug
>
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