[PATCH] btrfs: relocation: fix unused variable

[PATCH] btrfs: relocation: fix unused variable

[Anders Roxell]

When CONFIG_BRTFS_ASSERT isn't enabled, variable root_objectid isn't used.

fs/btrfs/relocation.c: In function ‘insert_dirty_subv’:
fs/btrfs/relocation.c:2138:6: warning: unused variable ‘root_objectid’ [-Wunused-variable]
  u64 root_objectid = root->root_key.objectid;
      ^~~~~~~~~~~~~

Reworked by adding a runtime check in the assfail function instead of
the '#ifdef CONFIG_BTRFS_ASSERT #else ...", so the compiler sees the
condition being passed into an inline function after preprocessing.

Fixes: 7b837199c581 ("btrfs: relocation: Delay reloc tree deletion after merge_reloc_roots()")
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
---
 fs/btrfs/ctree.h | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index de23a7ea396d..ad7d079f2cae 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3521,21 +3521,18 @@ do {								\
 	rcu_read_unlock();					\
 } while (0)
 
-#ifdef CONFIG_BTRFS_ASSERT
-
 __cold
 static inline void assfail(const char *expr, const char *file, int line)
 {
-	pr_err("assertion failed: %s, file: %s, line: %d\n",
-	       expr, file, line);
-	BUG();
+	if (IS_ENABLED(CONFIG_BTRFS_ASSERT)) {
+		pr_err("assertion failed: %s, file: %s, line: %d\n",
+		       expr, file, line);
+		BUG();
+	}
 }
 
 #define ASSERT(expr)	\
 	(likely(expr) ? (void)0 : assfail(#expr, __FILE__, __LINE__))
-#else
-#define ASSERT(expr)	((void)0)
-#endif
 
 /*
  * Use that for functions that are conditionally exported for sanity tests but
-- 
2.19.2

Re: [PATCH] btrfs: relocation: fix unused variable

[David Sterba]

On Tue, Jan 29, 2019 at 02:01:46PM +0100, Anders Roxell wrote:
> When CONFIG_BRTFS_ASSERT isn't enabled, variable root_objectid isn't used.
> 
> fs/btrfs/relocation.c: In function ‘insert_dirty_subv’:
> fs/btrfs/relocation.c:2138:6: warning: unused variable ‘root_objectid’ [-Wunused-variable]
>   u64 root_objectid = root->root_key.objectid;
>       ^~~~~~~~~~~~~
> 
> Reworked by adding a runtime check in the assfail function instead of
> the '#ifdef CONFIG_BTRFS_ASSERT #else ...", so the compiler sees the
> condition being passed into an inline function after preprocessing.

I've fixed the warning by avoiding the local variable but I like your
fix in general, thanks.

Re: [PATCH] btrfs: relocation: fix unused variable

[David Sterba]

On Tue, Jan 29, 2019 at 04:21:27PM +0100, David Sterba wrote:
> On Tue, Jan 29, 2019 at 02:01:46PM +0100, Anders Roxell wrote:
> > When CONFIG_BRTFS_ASSERT isn't enabled, variable root_objectid isn't used.
> > 
> > fs/btrfs/relocation.c: In function ‘insert_dirty_subv’:
> > fs/btrfs/relocation.c:2138:6: warning: unused variable ‘root_objectid’ [-Wunused-variable]
> >   u64 root_objectid = root->root_key.objectid;
> >       ^~~~~~~~~~~~~
> > 
> > Reworked by adding a runtime check in the assfail function instead of
> > the '#ifdef CONFIG_BTRFS_ASSERT #else ...", so the compiler sees the
> > condition being passed into an inline function after preprocessing.
> 
> I've fixed the warning by avoiding the local variable but I like your
> fix in general, thanks.

Committed with this changelog:

"btrfs: let the assertion expression compile in all configs

 A compiler warning (in a patch in development) pointed to a variable
 that was used only inside and ASSERT:

   u64 root_objectid = root->root_key.objectid;
   ASSERT(root_objectid == ...);

   fs/btrfs/relocation.c: In function ‘insert_dirty_subv’:
   fs/btrfs/relocation.c:2138:6: warning: unused variable ‘root_objectid’ [-Wunused-variable]
     u64 root_objectid = root->root_key.objectid;
	 ^~~~~~~~~~~~~

 When CONFIG_BRTFS_ASSERT isn't enabled, variable root_objectid isn't used.

 Rework the assertion helper by adding a runtime check instead of the
 '#ifdef CONFIG_BTRFS_ASSERT #else ...", so the compiler sees the
 condition being passed into an inline function after preprocessing."