On 21.08.24 12:03, Qi Zheng wrote:
On 2024/8/21 17:53, David Hildenbrand wrote:
On 21.08.24 11:51, Qi Zheng wrote:
On 2024/8/21 17:41, David Hildenbrand wrote:
On 21.08.24 11:24, Qi Zheng wrote:
On 2024/8/21 17:17, LEROY Christophe wrote:
Le 21/08/2024 à 10:18, Qi Zheng a écrit :
In handle_pte_fault(), we may modify the vmf->pte after acquiring the
vmf->ptl, so convert it to using pte_offset_map_maywrite_nolock().
But
since we already do the pte_same() check, so there is no need to get
pmdval to do pmd_same() check, just pass NULL to pmdvalp parameter.
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
mm/memory.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 93c0c25433d02..d3378e98faf13 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5504,9 +5504,14 @@ static vm_fault_t handle_pte_fault(struct
vm_fault *vmf)
* pmd by anon khugepaged, since that takes mmap_lock in
write
* mode; but shmem or file collapse to THP could still
morph
* it into a huge pmd: just retry later if so.
+ *
+ * Use the maywrite version to indicate that vmf->pte
will be
+ * modified, but since we will use pte_same() to detect the
+ * change of the pte entry, there is no need to get pmdval.
*/
- 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" :)
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?
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.
--
Cheers,
David / dhildenb
