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

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Date:   Fri, 17 Jan 2020 17:50:19 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     David Sterba <dsterba@...e.cz>,
        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 17, 2020 at 09:28:05AM -0600, Josh Poimboeuf wrote:
> 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?

So Co-developed-by: or "based on patch from Josh", or something else?

> > 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?

I don't understand what you mean, the helper is not called directly (and
build does not fail with or without CONFIG_BTRFS_ASSERT), but always as
ASSERT, so I don't see what needs to be updated.