[tip:perf/urgent] perf: Find_get_context: fix the per-cpu-counter check

[tip-bot for Oleg Nesterov]

Commit-ID:  22a4ec729017ba613337a28f306f94ba5023fe2e
Gitweb:     http://git.kernel.org/tip/22a4ec729017ba613337a28f306f94ba5023fe2e
Author:     Oleg Nesterov <oleg@xxxxxxxxxx>
AuthorDate: Tue, 18 Jan 2011 17:10:08 +0100
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Tue, 18 Jan 2011 19:34:23 +0100

perf: Find_get_context: fix the per-cpu-counter check

If task == NULL, find_get_context() should always check that cpu
is correct.

Afaics, the bug was introduced by 38a81da2 "perf events: Clean
up pid passing", but even before that commit "&& cpu != -1" was
not exactly right, -ESRCH from find_task_by_vpid() is not
accurate.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Prasad <prasad@xxxxxxxxxxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Cc: gregkh@xxxxxxx
Cc: stable@xxxxxxxxxx
LKML-Reference: <20110118161008.GB693@xxxxxxxxxx>
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 76be4c7..a962b19 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -2228,7 +2228,7 @@ find_get_context(struct pmu *pmu, struct task_struct *task, int cpu)
 	unsigned long flags;
 	int ctxn, err;
 
-	if (!task && cpu != -1) {
+	if (!task) {
 		/* Must be root to operate on a CPU event: */
 		if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
 			return ERR_PTR(-EACCES);
--
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