linux-kernel - [205/272] perf: Find_get_context: fix the per-cpu-counter check

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Message-Id: <20110216001445.654656926@clark.kroah.org>
Date:	Tue, 15 Feb 2011 16:14:22 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Alan Stern <stern@...land.harvard.edu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Prasad <prasad@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...hat.com>, Ingo Molnar <mingo@...e.hu>
Subject: [205/272] perf: Find_get_context: fix the per-cpu-counter check

2.6.37-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Oleg Nesterov <oleg@...hat.com>

commit 22a4ec729017ba613337a28f306f94ba5023fe2e upstream.

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>
Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Alan Stern <stern@...land.harvard.edu>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Prasad <prasad@...ux.vnet.ibm.com>
Cc: Roland McGrath <roland@...hat.com>
LKML-Reference: <20110118161008.GB693@...hat.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

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

--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -2100,7 +2100,7 @@ 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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