linux-kernel - [PATCH 1/2] perf: find_get_context: fix the per-cpu-counter check

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Message-ID: <20110118161008.GB693@redhat.com>
Date:	Tue, 18 Jan 2011 17:10:08 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Prasad <prasad@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...hat.com>, gregkh@...e.de,
	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: [PATCH 1/2] 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@...hat.com>
---

 kernel/perf_event.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- git/kernel/perf_event.c~1_find_get_context	2011-01-14 18:21:05.000000000 +0100
+++ git/kernel/perf_event.c	2011-01-18 16:56:40.000000000 +0100
@@ -2228,7 +2228,7 @@ find_get_context(struct pmu *pmu, struct
 	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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