[dm-devel] [PATCH] branch-check: fix long->int truncation when profiling branches

[Mikulas Patocka]

On Mon, 4 Jun 2018, Steven Rostedt wrote:

> On Wed, 30 May 2018 08:19:22 -0400 (EDT)
> Mikulas Patocka <mpatocka at redhat.com> wrote:
> 
> > The function __builtin_expect returns long type (see the gcc
> > documentation), and so do macros likely and unlikely. Unfortunatelly, when
> > CONFIG_PROFILE_ANNOTATED_BRANCHES is selected, the macros likely and
> > unlikely expand to __branch_check__ and __branch_check__ truncates the
> 
> Nice catch.
> 
> > long type to int. This unintended truncation may cause bugs in various
> > kernel code (we found a bug in dm-writecache because of it), so it's
> 
> I'm curious to what that bug was.

printk("%ld", writecache_has_error(wc))

... and writecache_has_error was defined as
#define writecache_has_error(wc)	(unlikely(READ_ONCE((wc)->error)))

Mikulas