linux-kernel - Re: linux-next: Tree for Dec 6 (objtool, lots in btrfs)

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Date:   Fri, 17 Jan 2020 09:28:05 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     David Sterba <dsterba@...e.cz>
Cc:     Randy Dunlap <rdunlap@...radead.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Btrfs <linux-btrfs@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: linux-next: Tree for Dec 6 (objtool, lots in btrfs)

On Fri, Jan 10, 2020 at 08:46:22PM +0100, David Sterba wrote:
> On Tue, Dec 17, 2019 at 04:29:54PM +0100, David Sterba wrote:
> > Separating the definitions by #ifdef looks ok, I'd rather do separate
> > definitions of ASSERT too, to avoid the ternary operator. I'll send the
> > patch.
> 
> Subject: [PATCH] btrfs: separate definition of assertion failure handlers
> 
> There's a report where objtool detects unreachable instructions, eg.:
> 
>   fs/btrfs/ctree.o: warning: objtool: btrfs_search_slot()+0x2d4: unreachable instruction
> 
> This seems to be a false positive due to compiler version. The cause is
> in the ASSERT macro implementation that does the conditional check as
> IS_DEFINED(CONFIG_BTRFS_ASSERT) and not an #ifdef.
> 
> To avoid that, use the ifdefs directly.
> 
> CC: Josh Poimboeuf <jpoimboe@...hat.com>
> Reported-by: Randy Dunlap <rdunlap@...radead.org>
> Signed-off-by: David Sterba <dsterba@...e.com>
> ---
>  fs/btrfs/ctree.h | 20 ++++++++++++--------
>  1 file changed, 12 insertions(+), 8 deletions(-)

This looks quite similar to my patch, would you mind giving me
attribution?

> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 569931dd0ce5..f90b82050d2d 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -3157,17 +3157,21 @@ do {								\
>  	rcu_read_unlock();					\
>  } while (0)
>  
> -__cold
> -static inline void assfail(const char *expr, const char *file, int line)
> +#ifdef CONFIG_BTRFS_ASSERT
> +__cold __noreturn
> +static inline void assertfail(const char *expr, const char *file, int line)
>  {
> -	if (IS_ENABLED(CONFIG_BTRFS_ASSERT)) {
> -		pr_err("assertion failed: %s, in %s:%d\n", expr, file, line);
> -		BUG();
> -	}
> +	pr_err("assertion failed: %s, in %s:%d\n", expr, file, line);
> +	BUG();

assertfail() is definitely better than "assfail", but shouldn't you
update the callers so it doesn't break the build?

-- 
Josh