mm: don't play games with pinned pages in clear_page_refs

Turning a pinned page read-only breaks the pinning after COW.  Don't do it.

The whole "track page soft dirty" state doesn't work with pinned pages
anyway, since the page might be dirtied by the pinning entity without
ever being noticed in the page tables.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index ab7d700b2caa4bcc79dac3bfc1e8831ee7df4147..602e3a52884d883c639420e426b539fd74ef35c5 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1035,6 +1035,25 @@ struct clear_refs_private {
 };
 
 #ifdef CONFIG_MEM_SOFT_DIRTY
+
+#define is_cow_mapping(flags) (((flags) & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE)
+
+static inline bool pte_is_pinned(struct vm_area_struct *vma, unsigned long addr, pte_t pte)
+{
+       struct page *page;
+
+       if (!pte_write(pte))
+               return false;
+       if (!is_cow_mapping(vma->vm_flags))
+               return false;
+       if (likely(!atomic_read(&vma->vm_mm->has_pinned)))
+               return false;
+       page = vm_normal_page(vma, addr, pte);
+       if (!page)
+               return false;
+       return page_maybe_dma_pinned(page);
+}
+
 static inline void clear_soft_dirty(struct vm_area_struct *vma,
                unsigned long addr, pte_t *pte)
 {
@@ -1049,6 +1068,8 @@ static inline void clear_soft_dirty(struct vm_area_struct *vma,
        if (pte_present(ptent)) {
                pte_t old_pte;
 
+               if (pte_is_pinned(vma, addr, ptent))
+                       return;
                old_pte = ptep_modify_prot_start(vma, addr, pte);
                ptent = pte_wrprotect(old_pte);
                ptent = pte_clear_soft_dirty(ptent);