linux-kernel - Re: [PATCH 4/5] mm: gup: fix potential pgmap refcnt leak in __gup_device

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Message-Id: <20210807114545.eaee318909a9215c4e056aa3@linux-foundation.org>
Date:   Sat, 7 Aug 2021 11:45:45 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Miaohe Lin <linmiaohe@...wei.com>, <imbrenda@...ux.ibm.com>,
        <kirill.shutemov@...ux.intel.com>, <jack@...e.cz>,
        <jhubbard@...dia.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/5] mm: gup: fix potential pgmap refcnt leak in
 __gup_device_huge()

On Sat, 7 Aug 2021 11:41:12 -0700 Andrew Morton <akpm@...ux-foundation.org> wrote:

> We can simplify further, and remove the troublesome multiple return points?
> 

oops.

--- a/mm/gup.c~mm-gup-fix-potential-pgmap-refcnt-leak-in-__gup_device_huge-fix-fix
+++ a/mm/gup.c
@@ -2240,6 +2240,7 @@ static int __gup_device_huge(unsigned lo
 {
 	int nr_start = *nr;
 	struct dev_pagemap *pgmap = NULL;
+	int ret = 1;
 
 	do {
 		struct page *page = pfn_to_page(pfn);
@@ -2247,12 +2248,14 @@ static int __gup_device_huge(unsigned lo
 		pgmap = get_dev_pagemap(pfn, pgmap);
 		if (unlikely(!pgmap)) {
 			undo_dev_pagemap(nr, nr_start, flags, pages);
+			ret = 0;
 			break;
 		}
 		SetPageReferenced(page);
 		pages[*nr] = page;
 		if (unlikely(!try_grab_page(page, flags))) {
 			undo_dev_pagemap(nr, nr_start, flags, pages);
+			ret = 0;
 			break;
 		}
 		(*nr)++;
@@ -2260,7 +2263,7 @@ static int __gup_device_huge(unsigned lo
 	} while (addr += PAGE_SIZE, addr != end);
 
 	put_dev_pagemap(pgmap);
-	return 1;
+	return ret;
 }
 
 static int __gup_device_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,

Not sure if it's worth bothering, really...