linux-kernel - [PATCH] reiserfs: avoid uninitialized variable use

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Date:	Fri, 27 May 2016 22:22:36 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	unlisted-recipients:; (no To-header on input)
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>, reiserfs-devel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] reiserfs: avoid uninitialized variable use

I got this warning on an ARM64 allmodconfig build with gcc-5.3:

fs/reiserfs/ibalance.c: In function 'balance_internal':
fs/reiserfs/ibalance.c:1158:3: error: 'new_insert_key' may be used uninitialized in this function [-Werror=maybe-uninitialized]
   memcpy(new_insert_key_addr, &new_insert_key, KEY_SIZE);

The warning is correct, in fact both new_insert_key and new_insert_ptr
are only updated inside of an if() block, but used at the end of
the function.

Looking at how the balance_internal() function gets called, it
is clear that this is harmless because the caller never uses the
updated arrays, they are initialized from balance_leaf_new_nodes()
and then passed into balance_internal().

This has not changed at all since the start of the git history,
but apparently the warning has only recently appeared.

This modifies the function to only update the two argument variables
when the new_insert_key and new_insert_ptr have been updated, to
get rid of the warning.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
I thought I had send this on May 12 when I first became aware of
the warning, but I can't find a reference to that now on any
mailing list archives, and I'm not sure who is picking up
reiserfs patches these days.

The warning is now one of the few 'allmodconfig' warnings for
arm64 and possibly some other architectures.

 fs/reiserfs/ibalance.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/reiserfs/ibalance.c b/fs/reiserfs/ibalance.c
index b751eea32e20..6dcc38f132f5 100644
--- a/fs/reiserfs/ibalance.c
+++ b/fs/reiserfs/ibalance.c
@@ -1138,6 +1138,9 @@ int balance_internal(struct tree_balance *tb,
 		       S_new);

 		/* S_new is released in unfix_nodes */
+
+		memcpy(new_insert_key_addr, &new_insert_key, KEY_SIZE);
+		insert_ptr[0] = new_insert_ptr;
 	}

 	n = B_NR_ITEMS(tbSh);	/*number of items in S[h] */
@@ -1153,8 +1156,5 @@ int balance_internal(struct tree_balance *tb,
 				       insert_ptr);
 	}

-	memcpy(new_insert_key_addr, &new_insert_key, KEY_SIZE);
-	insert_ptr[0] = new_insert_ptr;
-
 	return order;
 }
-- 
2.7.0