[tip:perf/urgent] perf_event: Fix incorrect range check on cpu number

[tip-bot for Paul Mackerras]

Commit-ID:  0f624e7e5625f4c30c836b7a5decfe2553582391
Gitweb:     http://git.kernel.org/tip/0f624e7e5625f4c30c836b7a5decfe2553582391
Author:     Paul Mackerras <paulus@xxxxxxxxx>
AuthorDate: Tue, 15 Dec 2009 19:40:32 +1100
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Tue, 15 Dec 2009 13:09:55 +0100

perf_event: Fix incorrect range check on cpu number

It is quite legitimate for CPUs to be numbered sparsely, meaning
that it possible for an online CPU to have a number which is
greater than the total count of possible CPUs.

Currently find_get_context() has a sanity check on the cpu
number where it checks it against num_possible_cpus().  This
test can fail for a legitimate cpu number if the
cpu_possible_mask is sparsely populated.

This fixes the problem by checking the CPU number against
nr_cpumask_bits instead, since that is the appropriate check to
ensure that the cpu number is same to pass to cpu_isset()
subsequently.

Reported-by: Michael Neuling <mikey@xxxxxxxxxxx>
Signed-off-by: Paul Mackerras <paulus@xxxxxxxxx>
Tested-by: Michael Neuling <mikey@xxxxxxxxxxx>
Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
LKML-Reference: <20091215084032.GA18661@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 kernel/perf_event.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index d891ec4..8823b08 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1603,7 +1603,7 @@ static struct perf_event_context *find_get_context(pid_t pid, int cpu)
 		if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
 			return ERR_PTR(-EACCES);
 
-		if (cpu < 0 || cpu > num_possible_cpus())
+		if (cpu < 0 || cpu >= nr_cpumask_bits)
 			return ERR_PTR(-EINVAL);
 
 		/*
--
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