mm/gup: take mmap_lock in get_dump_page()

Properly take the mmap_lock before calling into the GUP code from get_dump_page(); and play nice, allowing the GUP code to drop the mmap_lock if it has to sleep. As Linus pointed out, we don't actually need the VMA because __get_user_pages() will flush the dcache for us if necessary. Signed-off-by: Jann Horn <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Acked-by: Linus Torvalds <[email protected]> Cc: Christoph Hellwig <[email protected]> Cc: Alexander Viro <[email protected]> Cc: "Eric W . Biederman" <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: Hugh Dickins <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Linus Torvalds <[email protected]>
berg · Oct 16, 2020 · 7f3bfab · 7f3bfab
1 parent a07279c
commit 7f3bfab
Showing 1 changed file with 10 additions and 6 deletions.
diff --git a/mm/gup.c b/mm/gup.c
@@ -1547,19 +1547,23 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
  * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
  * allowing a hole to be left in the corefile to save diskspace.
  *
- * Called without mmap_lock, but after all other threads have been killed.
+ * Called without mmap_lock (takes and releases the mmap_lock by itself).
  */
 #ifdef CONFIG_ELF_CORE
 struct page *get_dump_page(unsigned long addr)
 {
-	struct vm_area_struct *vma;
+	struct mm_struct *mm = current->mm;
 	struct page *page;
+	int locked = 1;
+	int ret;
 
-	if (__get_user_pages_locked(current->mm, addr, 1, &page, &vma, NULL,
-				    FOLL_FORCE | FOLL_DUMP | FOLL_GET) < 1)
+	if (mmap_read_lock_killable(mm))
 		return NULL;
-	flush_cache_page(vma, addr, page_to_pfn(page));
-	return page;
+	ret = __get_user_pages_locked(mm, addr, 1, &page, NULL, &locked,
+				      FOLL_FORCE | FOLL_DUMP | FOLL_GET);
+	if (locked)
+		mmap_read_unlock(mm);
+	return (ret == 1) ? page : NULL;
 }
 #endif /* CONFIG_ELF_CORE */