mm: gup: fix potential pgmap refcnt leak in __gup_device_huge()

When failed to try_grab_page, put_dev_pagemap() is missed.  So pgmap
refcnt will leak in this case.  Also we remove the check for pgmap against
NULL as it's also checked inside the put_dev_pagemap().

[akpm@linux-foundation.org: simplify, cleanup]
[akpm@linux-foundation.org: fix return value]

Link: https://lkml.kernel.org/r/20210807093620.21347-5-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Fixes: 3faa52c03f44 ("mm/gup: track FOLL_PIN pages")
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/gup.c b/mm/gup.c
index 9f5b9a93ae21f4dec299eace1d32e8c3d3814e8d..a10c48ef613c9377b64c76014c80a8d0b878ca4c 100644 (file)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2240,6 +2240,7 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
 {
        int nr_start = *nr;
        struct dev_pagemap *pgmap = NULL;
+       int ret = 1;
 
        do {
                struct page *page = pfn_to_page(pfn);
@@ -2247,21 +2248,22 @@ static int __gup_device_huge(unsigned long pfn, unsigned long addr,
                pgmap = get_dev_pagemap(pfn, pgmap);
                if (unlikely(!pgmap)) {
                        undo_dev_pagemap(nr, nr_start, flags, pages);
-                       return 0;
+                       ret = 0;
+                       break;
                }
                SetPageReferenced(page);
                pages[*nr] = page;
                if (unlikely(!try_grab_page(page, flags))) {
                        undo_dev_pagemap(nr, nr_start, flags, pages);
-                       return 0;
+                       ret = 0;
+                       break;
                }
                (*nr)++;
                pfn++;
        } while (addr += PAGE_SIZE, addr != end);
 
-       if (pgmap)
-               put_dev_pagemap(pgmap);
-       return 1;
+       put_dev_pagemap(pgmap);
+       return ret;
 }
 
 static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,