On Wed 17-05-17 11:16:38, Ross Zwisler wrote:
> When the pmd_devmap() checks were added by:
>
> commit 5c7fb56e5e3f ("mm, dax: dax-pmd vs thp-pmd vs hugetlbfs-pmd")
>
> to add better support for DAX huge pages, they were all added to the end of
> if() statements after existing pmd_trans_huge() checks. So, things like:
>
> - if (pmd_trans_huge(*pmd))
> + if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd))
>
> When further checks were added after pmd_trans_unstable() checks by:
>
> commit 7267ec008b5c ("mm: postpone page table allocation until we have page
> to map")
>
> they were also added at the end of the conditional:
>
> + if (pmd_trans_unstable(fe->pmd) || pmd_devmap(*fe->pmd))
>
> This ordering is fine for pmd_trans_huge(), but doesn't work for
> pmd_trans_unstable(). This is because DAX huge pages trip the bad_pmd()
> check inside of pmd_none_or_trans_huge_or_clear_bad() (called by
> pmd_trans_unstable()), which prints out a warning and returns 1. So, we do
> end up doing the right thing, but only after spamming dmesg with suspicious
> looking messages:
>
> mm/pgtable-generic.c:39: bad pmd ffff8808daa49b88(84000001006000a5)
>
> Reorder these checks so that pmd_devmap() is checked first, avoiding the
> error messages.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Fixes: commit 7267ec008b5c ("mm: postpone page table allocation until we have page to map")
> Cc: stable@xxxxxxxxxxxxxxx
With the change requested by Dave this looks good to me. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> mm/memory.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 6ff5d72..1ee269d 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3061,7 +3061,7 @@ static int pte_alloc_one_map(struct vm_fault *vmf)
> * through an atomic read in C, which is what pmd_trans_unstable()
> * provides.
> */
> - if (pmd_trans_unstable(vmf->pmd) || pmd_devmap(*vmf->pmd))
> + if (pmd_devmap(*vmf->pmd) || pmd_trans_unstable(vmf->pmd))
> return VM_FAULT_NOPAGE;
>
> vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
> @@ -3690,7 +3690,7 @@ static int handle_pte_fault(struct vm_fault *vmf)
> vmf->pte = NULL;
> } else {
> /* See comment in pte_alloc_one_map() */
> - if (pmd_trans_unstable(vmf->pmd) || pmd_devmap(*vmf->pmd))
> + if (pmd_devmap(*vmf->pmd) || pmd_trans_unstable(vmf->pmd))
> return 0;
> /*
> * A regular pmd is established and it can't morph into a huge
> --
> 2.9.4
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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