linux-kernel - [PATCH 1/1] dax: initialize variable pfn before using it

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Message-Id: <20170903083000.587-1-nicolas.iooss_linux@m4x.org>
Date:   Sun,  3 Sep 2017 10:30:00 +0200
From:   Nicolas Iooss <nicolas.iooss_linux@....org>
To:     Matthew Wilcox <mawilcox@...rosoft.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nicolas Iooss <nicolas.iooss_linux@....org>
Subject: [PATCH 1/1] dax: initialize variable pfn before using it

Function dax_pmd_insert_mapping() contains the following code:

        pfn_t pfn;
        if (bdev_dax_pgoff(bdev, sector, size, &pgoff) != 0)
            goto fallback;
        /* ... */
    fallback:
      trace_dax_pmd_insert_mapping_fallback(inode, vmf, length, pfn, ret);

When the condition in the if statement fails, the function calls
trace_dax_pmd_insert_mapping_fallback() with an uninitialized pfn value.

This issue has been found while building the kernel with clang. The
compiler reported:

    fs/dax.c:1280:6: error: variable 'pfn' is used uninitialized
    whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
        if (bdev_dax_pgoff(bdev, sector, size, &pgoff) != 0)
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    fs/dax.c:1310:60: note: uninitialized use occurs here
      trace_dax_pmd_insert_mapping_fallback(inode, vmf, length, pfn, ret);
                                                                     ^~~

Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@....org>
---
 fs/dax.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index ab925dc6647a..20e6d76d6fff 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1283,7 +1283,7 @@ static int dax_pmd_insert_mapping(struct vm_fault *vmf, struct iomap *iomap,
 	void *ret = NULL, *kaddr;
 	long length = 0;
 	pgoff_t pgoff;
-	pfn_t pfn;
+	pfn_t pfn = {};
 	int id;
 
 	if (bdev_dax_pgoff(bdev, sector, size, &pgoff) != 0)
-- 
2.14.1