On 2024/8/22 20:19, David Hildenbrand wrote:

On 22.08.24 14:17, Qi Zheng wrote:

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Hi David,

On 2024/8/22 17:29, David Hildenbrand wrote:

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On 21.08.24 12:03, Qi Zheng wrote:

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[...]

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-        vmf->pte = pte_offset_map_nolock(vmf->vma->vm_mm,
vmf->pmd,
-                         vmf->address, &vmf->ptl);
+        vmf->pte = 
pte_offset_map_maywrite_nolock(vmf->vma->vm_mm,
+                              vmf->pmd, vmf->address,
+                              NULL, &vmf->ptl);

I think we discussed that passing NULL should be forbidden for that
function.

Yes, but for some maywrite case, there is no need to get pmdval to
do pmd_same() check. So I passed NULL and added a comment to
explain this.

I wonder if it's better to pass a dummy variable instead. One has to
think harder why that is required compared to blindly passing 
"NULL" :)

You are afraid that subsequent caller will abuse this function, right?

Yes! "oh, I don't need a pmdval, why would I? let's just pass NULL,
easy" :)

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My initial concern was that this would add a useless local vaiable, but
perhaps that is not a big deal.

How many of these "special" instances do we have?

We have 5 such special instances.

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Both are fine for me. ;)

Also no strong opinion, but having to pass a variable makes you think
what you are supposed to do with it and why it is not optional.

Yeah, I added 'BUG_ON(!pmdvalp);' in pte_offset_map_ro_nolock(), and
have updated the v2 version [1].

No BUG_ON please :) VM_WARN_ON_ONCE() is good enough.

Got it. Will do in the next version.