linux-kernel - [PATCH] percpu: fix unit_map[] verification in pcpu_setup_first

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Date:	Tue, 29 Sep 2009 01:19:13 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Tony Vroon <tony@...x.net>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH] percpu: fix unit_map[] verification in pcpu_setup_first_chunk()

pcpu_setup_first_chunk() incorrectly used NR_CPUS as the impossible
unit number while unit number can equal and go over NR_CPUS with
sparse unit map.  This triggers BUG_ON() spuriously on machines which
have non-power-of-two number of cpus.  Use UINT_MAX instead.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Tony Vroon <tony@...x.net>
---
Erghh... stupid mistake.  This should fix it.  Can you please verify?

Thanks.

 mm/percpu.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: work/mm/percpu.c
===================================================================
--- work.orig/mm/percpu.c
+++ work/mm/percpu.c
@@ -1604,7 +1604,7 @@ int __init pcpu_setup_first_chunk(const
 	unit_off = alloc_bootmem(nr_cpu_ids * sizeof(unit_off[0]));

 	for (cpu = 0; cpu < nr_cpu_ids; cpu++)
-		unit_map[cpu] = NR_CPUS;
+		unit_map[cpu] = UINT_MAX;
 	pcpu_first_unit_cpu = NR_CPUS;

 	for (group = 0, unit = 0; group < ai->nr_groups; group++, unit += i) {
@@ -1619,7 +1619,7 @@ int __init pcpu_setup_first_chunk(const
 				continue;

 			BUG_ON(cpu > nr_cpu_ids || !cpu_possible(cpu));
-			BUG_ON(unit_map[cpu] != NR_CPUS);
+			BUG_ON(unit_map[cpu] != UINT_MAX);

 			unit_map[cpu] = unit + i;
 			unit_off[cpu] = gi->base_offset + i * ai->unit_size;
@@ -1632,7 +1632,7 @@ int __init pcpu_setup_first_chunk(const
 	pcpu_nr_units = unit;

 	for_each_possible_cpu(cpu)
-		BUG_ON(unit_map[cpu] == NR_CPUS);
+		BUG_ON(unit_map[cpu] == UINT_MAX);

 	pcpu_nr_groups = ai->nr_groups;
 	pcpu_group_offsets = group_offsets;
--
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