[PATCH] btrfs: avoid uninitialized variable warning

[PATCH] btrfs: avoid uninitialized variable warning

[Arnd Bergmann]

With CONFIG_SMP and CONFIG_PREEMPT both disabled, gcc decides
to partially inline the get_state_failrec() function but cannot
figure out that means the failrec pointer is always valid
if the function returns success, which causes a harmless
warning:

fs/btrfs/extent_io.c: In function 'clean_io_failure':
fs/btrfs/extent_io.c:2131:4: error: 'failrec' may be used uninitialized in this function [-Werror=maybe-uninitialized]

This marks get_state_failrec() and set_state_failrec() both
as 'noinline', which avoids the warning in all cases for me,
and seems less ugly than adding a fake initialization.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 47dc196ae719 ("btrfs: use proper type for failrec in extent_state")
---
 fs/btrfs/extent_io.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 27577f1b10dc..76a0c8597d98 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1842,7 +1842,7 @@ out:
  * set the private field for a given byte offset in the tree.  If there isn't
  * an extent_state there already, this does nothing.
  */
-static int set_state_failrec(struct extent_io_tree *tree, u64 start,
+static noinline int set_state_failrec(struct extent_io_tree *tree, u64 start,
 		struct io_failure_record *failrec)
 {
 	struct rb_node *node;
@@ -1870,7 +1870,7 @@ out:
 	return ret;
 }
 
-static int get_state_failrec(struct extent_io_tree *tree, u64 start,
+static noinline int get_state_failrec(struct extent_io_tree *tree, u64 start,
 		struct io_failure_record **failrec)
 {
 	struct rb_node *node;
-- 
2.7.0

Re: [PATCH] btrfs: avoid uninitialized variable warning

[David Sterba]

On Mon, Feb 22, 2016 at 10:53:20PM +0100, Arnd Bergmann wrote:
> With CONFIG_SMP and CONFIG_PREEMPT both disabled, gcc decides
> to partially inline the get_state_failrec() function but cannot
> figure out that means the failrec pointer is always valid
> if the function returns success, which causes a harmless
> warning:
> 
> fs/btrfs/extent_io.c: In function 'clean_io_failure':
> fs/btrfs/extent_io.c:2131:4: error: 'failrec' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> This marks get_state_failrec() and set_state_failrec() both
> as 'noinline', which avoids the warning in all cases for me,
> and seems less ugly than adding a fake initialization.

Thanks for the analysis and the fix, works for me.