On 01/18/2018 03:22 PM, Matthew Wilcox wrote:
> On Thu, Jan 18, 2018 at 06:07:39AM -0800, Matthew Wilcox wrote:
>> On Thu, Jan 18, 2018 at 02:38:39PM +0100, Jan H. Schönherr wrote:
>>> The function follow_pte_pmd() can theoretically return after having
>>> acquired a PMD lock, even when DAX was not compiled with
>>> CONFIG_FS_DAX_PMD.
>>
>> I don't think it can. How would a PMD entry get into a DAX VMA if we
>> compiled the kernel without CONFIG_FS_DAX_PMD?
>
> How about this patch instead? Should shut up sparse nicely.
It would still skip the unlock, in case pmdp is !=NULL (and locked) after follow_pte_pmd().
So it wouldn't address, what I intended to address with the patch.
Regards
Jan
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 78b72c48374e..fea1b64d111b 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -586,6 +586,12 @@ pgoff_address(pgoff_t pgoff, struct vm_area_struct *vma)
> return address;
> }
>
> +#ifdef CONFIG_FS_DAX_PMD
> +#define dax_pmd(pmdp) pmdp
> +#else
> +#define dax_pmd(pmdp) 0
> +#endif
> +
> /* Walk all mappings of a given index of a file and writeprotect them */
> static void dax_mapping_entry_mkclean(struct address_space *mapping,
> pgoff_t index, unsigned long pfn)
> @@ -621,8 +627,7 @@ static void dax_mapping_entry_mkclean(struct address_space *mapping,
> *
> * See Documentation/vm/mmu_notifier.txt
> */
> - if (pmdp) {
> -#ifdef CONFIG_FS_DAX_PMD
> + if (dax_pmd(pmdp)) {
> pmd_t pmd;
>
> if (pfn != pmd_pfn(*pmdp))
> @@ -638,7 +643,6 @@ static void dax_mapping_entry_mkclean(struct address_space *mapping,
> set_pmd_at(vma->vm_mm, address, pmdp, pmd);
> unlock_pmd:
> spin_unlock(ptl);
> -#endif
> } else {
> if (pfn != pte_pfn(*ptep))
> goto unlock_pte;
>
