linux-kernel - [PATCH] mm/khugepaged: Initialize index and nr in collapse

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Date:   Tue, 25 Oct 2022 10:34:07 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Gautam Menghani <gautammenghani201@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        patches@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>,
        kernel test robot <lkp@...el.com>
Subject: [PATCH] mm/khugepaged: Initialize index and nr in collapse_file()

Clang warns (trimmed for brevity):

  mm/khugepaged.c:1729:7: warning: variable 'index' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
  mm/khugepaged.c:1716:6: warning: variable 'index' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
  mm/khugepaged.c:1729:7: warning: variable 'nr' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
  mm/khugepaged.c:1716:6: warning: variable 'nr' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]

There are two goto statements that will use index and nr before they
have been properly initialized. Zero initialize them so that they can be
safely used by the tracepoint at the end of the function.

Fixes: eae5270d3322 ("mm/khugepaged: add tracepoint to collapse_file()")
Link: https://github.com/ClangBuiltLinux/linux/issues/1749
Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 mm/khugepaged.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 977c0ff82c46..789db2f3fc06 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1702,12 +1702,12 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 {
 	struct address_space *mapping = file->f_mapping;
 	struct page *hpage;
-	pgoff_t index, end = start + HPAGE_PMD_NR;
+	pgoff_t index = 0, end = start + HPAGE_PMD_NR;
 	LIST_HEAD(pagelist);
 	XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
 	int nr_none = 0, result = SCAN_SUCCEED;
 	bool is_shmem = shmem_file(file);
-	int nr;
+	int nr = 0;
 
 	VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
 	VM_BUG_ON(start & (HPAGE_PMD_NR - 1));

base-commit: ec24a700584c4df869282bcd92b6d88329afe395
-- 
2.38.1