Re: [PATCH] dax, pmem: add support for msync

On Wed, Sep 02, 2015 at 12:41:44PM +0300, Boaz Harrosh wrote:

On 09/02/2015 12:37 PM, Boaz Harrosh wrote:

quoted

quoted

 
+               /*
+                * Make sure that for VM_MIXEDMAP VMA has both
+                * vm_ops->page_mkwrite and vm_ops->pfn_mkwrite or has none.
+                */
+               if ((vma->vm_ops->page_mkwrite || vma->vm_ops->pfn_mkwrite) &&
+                               vma->vm_flags & VM_MIXEDMAP) {
+                       VM_BUG_ON_VMA(!vma->vm_ops->page_mkwrite, vma);
+                       VM_BUG_ON_VMA(!vma->vm_ops->pfn_mkwrite, vma);

BTW: the page_mkwrite is used for reading of holes that put zero-pages at the radix tree.
     One can just map a single global zero-page in pfn-mode for that.

Kirill Hi. Please don't make these BUG_ONs its counter productive believe me.

This is VM_BUG_ON, not normal BUG_ON. VM_BUG_ON is under CONFIG_DEBUG_VM 
which is disabled on production kernels.

quoted

Please make them WARN_ON_ONCE() it is not a crashing bug to work like this.
(Actually it is not a bug at all in some cases, but we can relax that when a user
 comes up)

Thanks
Boaz

Second thought I do not like this patch. This is why we have xftests for, the fact of it
is that test 080 catches this. For me this is enough.

I don't insist on applying the patch. And I worry about false-positives.

An FS developer should test his code, and worst case we help him on ML, like we did
in this case.

Thanks
Boaz

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+               }
                addr = vma->vm_start;
                vm_flags = vma->vm_flags;
        } else if (vm_flags & VM_SHARED) {

-- 
 Kirill A. Shutemov

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