Re: [PATCH 1/2] arm64: Improve error reporting on set_pte_at() checks

Re: [PATCH 1/2] arm64: Improve error reporting on set_pte_at() checks

[Andrew Pinski]

On Tue, Dec 9, 2015 at 17:26:56, Catalin Marinas
<catalin.marinas@arm.com> wrote:
>
> Currently the BUG_ON() checks do not give enough information about the PTEs being set. This patch changes BUG_ON to WARN_ONCE and dumps the values of the old and new PTEs.


This change broke building the mantis driver:

In file included from ./arch/arm64/include/asm/io.h:30:0,
                 from drivers/media/pci/mantis/mantis_i2c.c:21:
./arch/arm64/include/asm/pgtable.h: In function ‘set_pte_at’:
./arch/arm64/include/asm/pgtable.h:281:3: error: implicit declaration
of function ‘BUILD_BUG_ON_INVALID’
[-Werror=implicit-function-declaration]
   VM_WARN_ONCE(!pte_young(pte),
   ^

Thanks,
Andrew Pinski

>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> ---
>   arch/arm64/include/asm/pgtable.h | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h
> b/arch/arm64/include/asm/pgtable.h
> index 7e074f93f383..002dc61a4dff 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -276,10 +276,13 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
>          * hardware updates of the pte (ptep_set_access_flags safely changes
>          * valid ptes without going through an invalid entry).
>          */
> -       if (IS_ENABLED(CONFIG_DEBUG_VM) && IS_ENABLED(CONFIG_ARM64_HW_AFDBM) &&
> -           pte_valid(*ptep)) {
> -               BUG_ON(!pte_young(pte));
> -               BUG_ON(pte_write(*ptep) && !pte_dirty(pte));
> +       if (IS_ENABLED(CONFIG_ARM64_HW_AFDBM) && pte_valid(*ptep)) {
> +               VM_WARN_ONCE(!pte_young(pte),
> +                            "%s: racy access flag clearing: %016llx -> %016llx",
> +                            __func__, pte_val(*ptep), pte_val(pte));
> +               VM_WARN_ONCE(pte_write(*ptep) && !pte_dirty(pte),
> +                            "%s: racy dirty state clearing: %016llx -> %016llx",
> +                            __func__, pte_val(*ptep), pte_val(pte));
>         }
>
>         set_pte(ptep, pte);
>
> _______________________________________________
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> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
>
>
>

Re: [PATCH 1/2] arm64: Improve error reporting on set_pte_at() checks

[James Morse]

Hi Andrew,

On 16/12/15 03:01, Andrew Pinski wrote:
> On Tue, Dec 9, 2015 at 17:26:56, Catalin Marinas
> <catalin.marinas@arm.com> wrote:
>>
>> Currently the BUG_ON() checks do not give enough information about the PTEs being set. This patch changes BUG_ON to WARN_ONCE and dumps the values of the old and new PTEs.
> 
> 
> This change broke building the mantis driver:
> 
> In file included from ./arch/arm64/include/asm/io.h:30:0,
>                  from drivers/media/pci/mantis/mantis_i2c.c:21:
> ./arch/arm64/include/asm/pgtable.h: In function ‘set_pte_at’:
> ./arch/arm64/include/asm/pgtable.h:281:3: error: implicit declaration
> of function ‘BUILD_BUG_ON_INVALID’
> [-Werror=implicit-function-declaration]
>    VM_WARN_ONCE(!pte_young(pte),
>    ^

This is due to a missing include in include/linux/mmdebug.h, which
Julien Grall saw with CONFIG_XEN & !CONFIG_DEBUG_VM. There was some
discussion at [0], and a patch at [1].

The quick-and-dirty workaround is to toggle CONFIG_DEBUG_VM. It should
be fixed in the next rc.


Thanks,

James

[0] https://lkml.org/lkml/2015/12/14/489
[1] http://www.spinics.net/lists/linux-mm/msg98868.html