* Shakeel Butt [off-list ref] [210525 19:45]:

On Tue, May 25, 2021 at 11:40 AM Liam Howlett [off-list ref] wrote:

quoted

[...]

quoted

quoted

+/*
+ * Walks the vma's mapping a page and mlocks the page if any locked vma's are
+ * found. Once one is found the page is locked and the scan can be terminated.
+ */

Can you please add that this requires the mmap_sem() lock to the
comments?

Why does this require mmap_sem() lock? Also mmap_sem() lock of which mm_struct?

Doesn't the mlock_vma_page() require the mmap_sem() for reading?  The
mm_struct in vma->vm_mm;


From what I can see, at least the following paths have mmap_lock held
for writing:

munlock_vma_pages_range() from __do_munmap()
munlokc_vma_pages_range() from remap_file_pages()

quoted

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+static bool page_mlock_one(struct page *page, struct vm_area_struct *vma,
+                              unsigned long address, void *unused)
+{
+     struct page_vma_mapped_walk pvmw = {
+             .page = page,
+             .vma = vma,
+             .address = address,
+     };
+
+     /* An un-locked vma doesn't have any pages to lock, continue the scan */
+     if (!(vma->vm_flags & VM_LOCKED))
+             return true;
+
+     while (page_vma_mapped_walk(&pvmw)) {
+             /* PTE-mapped THP are never mlocked */
+             if (!PageTransCompound(page))
+                     mlock_vma_page(page);
+             page_vma_mapped_walk_done(&pvmw);
+
+             /*
+              * no need to continue scanning other vma's if the page has
+              * been locked.
+              */
+             return false;
+     }
+
+     return true;
+}

munlock_vma_pages_range() comments still references try_to_{munlock|unmap}