mm/gup: make locked never NULL in the internal GUP functions

Now that NULL locked doesn't have a special meaning we can just make it
non-NULL in all cases and remove the special tests.

get_user_pages() and pin_user_pages() can safely pass in a locked = 1

get_user_pages_remote) and pin_user_pages_remote() can swap in a local
variable for locked if NULL is passed.

Remove all the NULL checks.

Link: https://lkml.kernel.org/r/9-v2-987e91b59705+36b-gup_tidy_jgg@nvidia.com
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/gup.c b/mm/gup.c
index 310fc6a..4ce88e0 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -879,9 +879,9 @@ unmap:
 }
 
 /*
- * mmap_lock must be held on entry.  If @locked != NULL and *@flags
- * does not include FOLL_NOWAIT, the mmap_lock may be released.  If it
- * is, *@locked will be set to 0 and -EBUSY returned.
+ * mmap_lock must be held on entry.  If @flags has FOLL_UNLOCKABLE but not
+ * FOLL_NOWAIT, the mmap_lock may be released.  If it is, *@locked will be set
+ * to 0 and -EBUSY returned.
  */
 static int faultin_page(struct vm_area_struct *vma,
                unsigned long address, unsigned int *flags, bool unshare,
@@ -930,8 +930,8 @@ static int faultin_page(struct vm_area_struct *vma,
                 * mmap lock in the page fault handler. Sanity check this.
                 */
                WARN_ON_ONCE(fault_flags & FAULT_FLAG_RETRY_NOWAIT);
-               if (locked)
-                       *locked = 0;
+               *locked = 0;
+
                /*
                 * We should do the same as VM_FAULT_RETRY, but let's not
                 * return -EBUSY since that's not reflecting the reality of
@@ -951,7 +951,7 @@ static int faultin_page(struct vm_area_struct *vma,
        }
 
        if (ret & VM_FAULT_RETRY) {
-               if (locked && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
+               if (!(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
                        *locked = 0;
                return -EBUSY;
        }
@@ -1062,14 +1062,12 @@ static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
  * appropriate) must be called after the page is finished with, and
  * before put_page is called.
  *
- * If @locked != NULL, *@locked will be set to 0 when mmap_lock is
- * released by an up_read().  That can happen if @gup_flags does not
- * have FOLL_NOWAIT.
+ * If FOLL_UNLOCKABLE is set without FOLL_NOWAIT then the mmap_lock may
+ * be released. If this happens *@locked will be set to 0 on return.
  *
- * A caller using such a combination of @locked and @gup_flags
- * must therefore hold the mmap_lock for reading only, and recognize
- * when it's been released.  Otherwise, it must be held for either
- * reading or writing and will not be released.
+ * A caller using such a combination of @gup_flags must therefore hold the
+ * mmap_lock for reading only, and recognize when it's been released. Otherwise,
+ * it must be held for either reading or writing and will not be released.
  *
  * In most cases, get_user_pages or get_user_pages_fast should be used
  * instead of __get_user_pages. __get_user_pages should be used only if
@@ -1121,7 +1119,7 @@ static long __get_user_pages(struct mm_struct *mm,
                                i = follow_hugetlb_page(mm, vma, pages, vmas,
                                                &start, &nr_pages, i,
                                                gup_flags, locked);
-                               if (locked && *locked == 0) {
+                               if (!*locked) {
                                        /*
                                         * We've got a VM_FAULT_RETRY
                                         * and we've lost mmap_lock.
@@ -1354,7 +1352,7 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
         * The internal caller expects GUP to manage the lock internally and the
         * lock must be released when this returns.
         */
-       if (locked && !*locked) {
+       if (!*locked) {
                if (mmap_read_lock_killable(mm))
                        return -EAGAIN;
                must_unlock = true;
@@ -1502,6 +1500,7 @@ long populate_vma_page_range(struct vm_area_struct *vma,
 {
        struct mm_struct *mm = vma->vm_mm;
        unsigned long nr_pages = (end - start) / PAGE_SIZE;
+       int local_locked = 1;
        int gup_flags;
        long ret;
 
@@ -1542,7 +1541,7 @@ long populate_vma_page_range(struct vm_area_struct *vma,
         * not result in a stack expansion that recurses back here.
         */
        ret = __get_user_pages(mm, start, nr_pages, gup_flags,
-                               NULL, NULL, locked);
+                               NULL, NULL, locked ? locked : &local_locked);
        lru_add_drain();
        return ret;
 }
@@ -1683,7 +1682,7 @@ static long __get_user_pages_locked(struct mm_struct *mm, unsigned long start,
         * The internal caller expects GUP to manage the lock internally and the
         * lock must be released when this returns.
         */
-       if (locked && !*locked) {
+       if (!*locked) {
                if (mmap_read_lock_killable(mm))
                        return -EAGAIN;
                must_unlock = true;
@@ -2222,11 +2221,14 @@ long get_user_pages_remote(struct mm_struct *mm,
                unsigned int gup_flags, struct page **pages,
                struct vm_area_struct **vmas, int *locked)
 {
+       int local_locked = 1;
+
        if (!is_valid_gup_args(pages, vmas, locked, &gup_flags,
                               FOLL_TOUCH | FOLL_REMOTE))
                return -EINVAL;
 
-       return __get_user_pages_locked(mm, start, nr_pages, pages, vmas, locked,
+       return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
+                                      locked ? locked : &local_locked,
                                       gup_flags);
 }
 EXPORT_SYMBOL(get_user_pages_remote);
@@ -2261,11 +2263,13 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
                unsigned int gup_flags, struct page **pages,
                struct vm_area_struct **vmas)
 {
+       int locked = 1;
+
        if (!is_valid_gup_args(pages, vmas, NULL, &gup_flags, FOLL_TOUCH))
                return -EINVAL;
 
        return __get_user_pages_locked(current->mm, start, nr_pages, pages,
-                                      vmas, NULL, gup_flags);
+                                      vmas, &locked, gup_flags);
 }
 EXPORT_SYMBOL(get_user_pages);
 
@@ -3158,10 +3162,13 @@ long pin_user_pages_remote(struct mm_struct *mm,
                           unsigned int gup_flags, struct page **pages,
                           struct vm_area_struct **vmas, int *locked)
 {
+       int local_locked = 1;
+
        if (!is_valid_gup_args(pages, vmas, locked, &gup_flags,
                               FOLL_PIN | FOLL_TOUCH | FOLL_REMOTE))
                return 0;
-       return __gup_longterm_locked(mm, start, nr_pages, pages, vmas, locked,
+       return __gup_longterm_locked(mm, start, nr_pages, pages, vmas,
+                                    locked ? locked : &local_locked,
                                     gup_flags);
 }
 EXPORT_SYMBOL(pin_user_pages_remote);
@@ -3187,10 +3194,12 @@ long pin_user_pages(unsigned long start, unsigned long nr_pages,
                    unsigned int gup_flags, struct page **pages,
                    struct vm_area_struct **vmas)
 {
+       int locked = 1;
+
        if (!is_valid_gup_args(pages, vmas, NULL, &gup_flags, FOLL_PIN))
                return 0;
        return __gup_longterm_locked(current->mm, start, nr_pages,
-                                    pages, vmas, NULL, gup_flags);
+                                    pages, vmas, &locked, gup_flags);
 }
 EXPORT_SYMBOL(pin_user_pages);