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From: Mikulas Patocka <mpatocka@redhat.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>, Alasdair Kergon <agk@redhat.com>,
	Mike Snitzer <snitzer@redhat.com>,
	dm-devel@redhat.com, linux-kernel@vger.kernel.org,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH] branch-check: fix long->int truncation when profiling branches
Date: Mon, 4 Jun 2018 16:54:44 -0400 (EDT)	[thread overview]
Message-ID: <alpine.LRH.2.02.1806041653260.18196@file01.intranet.prod.int.rdu2.redhat.com> (raw)
In-Reply-To: <20180604165024.3be78887@gandalf.local.home>



On Mon, 4 Jun 2018, Steven Rostedt wrote:

> On Wed, 30 May 2018 08:19:22 -0400 (EDT)
> Mikulas Patocka <mpatocka@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

      reply	other threads:[~2018-06-04 20:54 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-28 15:54 [PATCH] dm: writecache: fix format string warning Arnd Bergmann
2018-05-29 18:09 ` Mike Snitzer
2018-05-30 12:13 ` [PATCH] " Mikulas Patocka
2018-05-30 12:19 ` [PATCH] branch-check: fix long->int truncation when profiling branches Mikulas Patocka
2018-06-04 20:50   ` Steven Rostedt
2018-06-04 20:54     ` Mikulas Patocka [this message]

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