linux-kernel - [PATCH v2 3/3] mm/nommu: drop unlikely behind BUG

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Date:	Mon,  5 Oct 2015 21:26:06 +0800
From:	Geliang Tang <geliangtang@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Joonsoo Kim <js1304@...il.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Leon Romanovsky <leon@...n.nu>, Oleg Nesterov <oleg@...hat.com>
Cc:	Geliang Tang <geliangtang@....com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/3] mm/nommu: drop unlikely behind BUG_ON()

(1) For !CONFIG_BUG cases, the bug call is a no-op, so we couldn't care
less and the change is ok.

(2) ppc and mips, which HAVE_ARCH_BUG_ON, do not rely on branch predictions
as it seems to be pointless[1] and thus callers should not be trying to
push an optimization in the first place.

(3) For CONFIG_BUG and !HAVE_ARCH_BUG_ON cases, BUG_ON() contains an
unlikely compiler flag already.

Hence, we can drop unlikely behind BUG_ON().

[1] http://lkml.iu.edu/hypermail/linux/kernel/1101.3/02289.html

Signed-off-by: Geliang Tang <geliangtang@....com>
Acked-by: Davidlohr Bueso <dave@...olabs.net>
---
Changes in v2:
 - Just rewrite the commit log.
---
 mm/nommu.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/nommu.c b/mm/nommu.c
index 1e0f168..92be862 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -578,16 +578,16 @@ static noinline void validate_nommu_regions(void)
 		return;
 
 	last = rb_entry(lastp, struct vm_region, vm_rb);
-	BUG_ON(unlikely(last->vm_end <= last->vm_start));
-	BUG_ON(unlikely(last->vm_top < last->vm_end));
+	BUG_ON(last->vm_end <= last->vm_start);
+	BUG_ON(last->vm_top < last->vm_end);
 
 	while ((p = rb_next(lastp))) {
 		region = rb_entry(p, struct vm_region, vm_rb);
 		last = rb_entry(lastp, struct vm_region, vm_rb);
 
-		BUG_ON(unlikely(region->vm_end <= region->vm_start));
-		BUG_ON(unlikely(region->vm_top < region->vm_end));
-		BUG_ON(unlikely(region->vm_start < last->vm_top));
+		BUG_ON(region->vm_end <= region->vm_start);
+		BUG_ON(region->vm_top < region->vm_end);
+		BUG_ON(region->vm_start < last->vm_top);
 
 		lastp = p;
 	}
-- 
2.5.0


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