linux-kernel - [tip:perf/core] perf: Avoid RCU vs preemption assumptions

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Message-ID: <tip-41945f6ccf1e86f87fddf6b32db9cf431c05fb54@git.kernel.org>
Date:	Tue, 21 Sep 2010 14:13:48 GMT
From:	tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	a.p.zijlstra@...llo.nl, tj@...nel.org, tglx@...utronix.de,
	mingo@...e.hu
Subject: [tip:perf/core] perf: Avoid RCU vs preemption assumptions

Commit-ID:  41945f6ccf1e86f87fddf6b32db9cf431c05fb54
Gitweb:     http://git.kernel.org/tip/41945f6ccf1e86f87fddf6b32db9cf431c05fb54
Author:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Thu, 16 Sep 2010 19:17:24 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Tue, 21 Sep 2010 13:55:44 +0200

perf: Avoid RCU vs preemption assumptions

The per-pmu per-cpu context patch converted things from
get_cpu_var() to this_cpu_ptr(), but that only works if
rcu_read_lock() actually disables preemption, and since
there is no such guarantee, we need to fix that.

Use the newly introduced {get,put}_cpu_ptr().

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Tejun Heo <tj@...nel.org>
LKML-Reference: <20100917093009.308453028@...llo.nl>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/perf_event.c |   18 ++++++++++++------
 1 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index baae136..c16158c 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -3836,18 +3836,20 @@ static void perf_event_task_event(struct perf_task_event *task_event)
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(pmu, &pmus, entry) {
-		cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
+		cpuctx = get_cpu_ptr(pmu->pmu_cpu_context);
 		perf_event_task_ctx(&cpuctx->ctx, task_event);
 
 		ctx = task_event->task_ctx;
 		if (!ctx) {
 			ctxn = pmu->task_ctx_nr;
 			if (ctxn < 0)
-				continue;
+				goto next;
 			ctx = rcu_dereference(current->perf_event_ctxp[ctxn]);
 		}
 		if (ctx)
 			perf_event_task_ctx(ctx, task_event);
+next:
+		put_cpu_ptr(pmu->pmu_cpu_context);
 	}
 	rcu_read_unlock();
 }
@@ -3969,16 +3971,18 @@ static void perf_event_comm_event(struct perf_comm_event *comm_event)
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(pmu, &pmus, entry) {
-		cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
+		cpuctx = get_cpu_ptr(pmu->pmu_cpu_context);
 		perf_event_comm_ctx(&cpuctx->ctx, comm_event);
 
 		ctxn = pmu->task_ctx_nr;
 		if (ctxn < 0)
-			continue;
+			goto next;
 
 		ctx = rcu_dereference(current->perf_event_ctxp[ctxn]);
 		if (ctx)
 			perf_event_comm_ctx(ctx, comm_event);
+next:
+		put_cpu_ptr(pmu->pmu_cpu_context);
 	}
 	rcu_read_unlock();
 }
@@ -4152,19 +4156,21 @@ got_name:
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(pmu, &pmus, entry) {
-		cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
+		cpuctx = get_cpu_ptr(pmu->pmu_cpu_context);
 		perf_event_mmap_ctx(&cpuctx->ctx, mmap_event,
 					vma->vm_flags & VM_EXEC);
 
 		ctxn = pmu->task_ctx_nr;
 		if (ctxn < 0)
-			continue;
+			goto next;
 
 		ctx = rcu_dereference(current->perf_event_ctxp[ctxn]);
 		if (ctx) {
 			perf_event_mmap_ctx(ctx, mmap_event,
 					vma->vm_flags & VM_EXEC);
 		}
+next:
+		put_cpu_ptr(pmu->pmu_cpu_context);
 	}
 	rcu_read_unlock();
 
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