Re: [PATCH -v6 2/2] Updating ctime and mtime for memory-mapped files

[Miklos Szeredi <miklos@szeredi.hu>]

> diff --git a/mm/msync.c b/mm/msync.c
> index 144a757..a1b3fc6 100644
> --- a/mm/msync.c
> +++ b/mm/msync.c
> @@ -14,6 +14,122 @@
>  #include <linux/syscalls.h>
>  #include <linux/sched.h>
>  
> +unsigned long masync_pte_range(struct vm_area_struct *vma, pmd_t *pdm,
> +		unsigned long addr, unsigned long end)
> +{
> +	pte_t *pte;
> +	spinlock_t *ptl;
> +
> +	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
> +	arch_enter_lazy_mmu_mode();
> +	do {
> +		pte_t ptent = *pte;
> +
> +		if (pte_none(ptent))
> +			continue;
> +
> +		if (!pte_present(ptent))
> +			continue;
> +
> +		if (pte_dirty(ptent) && pte_write(ptent)) {
> +			flush_cache_page(vma, addr, pte_pfn(ptent));

Hmm, I'm not sure flush_cache_page() is needed.  Or does does dirty
data in the cache somehow interfere with the page protection?

> +			ptent = ptep_clear_flush(vma, addr, pte);
> +			ptent = pte_wrprotect(ptent);
> +			set_pte_at(vma->vm_mnm, addr, pte, ptent);
> +		}
> +	} while (pte++, addr += PAGE_SIZE, addr != end);
> +	arch_leave_lazy_mmu_mode();
> +	pte_unmap_unlock(pte - 1, ptl);
> +
> +	return addr;
> +}
> +
> +unsigned long masync_pmd_range(struct vm_area_struct *vma, pud_t *pud,
> +		unsigned long addr, unsigned long end)
> +{
> +	pmd_t *pmd;
> +	unsigned long next;
> +
> +	pmd = pmd_offset(pud, addr);
> +	do {
> +		next = pmd_addr_end(addr, end);
> +		if (pmd_none_or_clear_bad(pmd))
> +			continue;
> +		next = masync_pte_range(vma, pmd, addr, next);
> +	} while (pmd++, addr = next, addr != end);
> +
> +	return addr;
> +}
> +
> +unsigned long masync_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
> +	       	unsigned long addr, unsigned long end)
> +{
> +	pud_t *pud;
> +	unsigned long next;
> +
> +	pud = pud_offset(pgd, addr);
> +	do {
> +		next = pud_addr_end(addr, end);
> +		if (pud_none_or_clear_bad(pud))
> +			continue;
> +		next = masync_pmd_range(vma, pud, addr, next);
> +	} while (pud++, addr = next, addr != end);
> +
> +	return addr;
> +}
> +
> +unsigned long masync_pgd_range()
> +{
> +	pgd_t *pgd;
> +	unsigned long next;
> +
> +	pgd = pgd_offset(vma->vm_mm, addr);
> +	do {
> +		next = pgd_addr_end(addr, end);
> +		if (pgd_none_of_clear_bad(pgd))
> +			continue;
> +		next = masync_pud_range(vma, pgd, addr, next);
> +	} while (pgd++, addr = next, addr != end);
> +
> +	return addr;
> +}
> +
> +int masync_vma_one(struct vm_area_struct *vma,
> +		unsigned long start, unsigned long end)
> +{
> +	if (start < vma->vm_start)
> +		start = vma->vm_start;
> +
> +	if (end > vma->vm_end)
> +		end = vma->vm_end;
> +
> +	masync_pgd_range(vma, start, end);
> +
> +	return 0;
> +}
> +
> +int masync_vma(struct vm_area_struct *vma, 
> +		unsigned long start, unsigned long end)
> +{
> +	struct address_space *mapping;
> +	struct vm_area_struct *vma_iter;
> +
> +	if (!(vma->vm_flags & VM_SHARED))
> +		return 0;
> +
> +	mapping = vma->vm_file->f_mapping;
> +
> +	if (!mapping_cap_account_dirty(mapping))
> +		return 0;
> +
> +	spin_lock(&mapping->i_mmap_lock);
> +	vma_prio_tree_foreach(vma_iter, &iter, &mapping->i_mmap, start, end)
> +		masync_vma_one(vma_iter, start, end);
> +	spin_unlock(&mapping->i_mmap_lock);

This is hoding i_mmap_lock for possibly quite long.  Isn't that going
to cause problems?

Miklos

> +
> +	return 0;
> +}
> +
>  /*
>   * MS_SYNC syncs the entire file - including mappings.
>   *
> 
> 
> 
>