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Subject[PATCH v3 1/2] perf/core: fix RCU problem with cgroup context switching code
Date
The RCU checker detected RCU violation in the cgroup switching routines
perf_cgroup_sched_in() and perf_cgroup_sched_out(). We were dereferencing
cgroup from task without hold the rcu lock. Fix this mov holding the
rcu read lock. We move the locking from perf_cgroup_switch() to avoid double
locking.

Signed-off-by: Stephane Eranian <eranian@google.com>
---
kernel/events/core.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 98a4b9d..ea0bdc5 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -489,7 +489,6 @@ static void perf_cgroup_switch(struct task_struct *task, int mode)
* we reschedule only in the presence of cgroup
* constrained events.
*/
- rcu_read_lock();

list_for_each_entry_rcu(pmu, &pmus, entry) {
cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
@@ -531,8 +530,6 @@ static void perf_cgroup_switch(struct task_struct *task, int mode)
}
}

- rcu_read_unlock();
-
local_irq_restore(flags);
}

@@ -542,6 +539,7 @@ static inline void perf_cgroup_sched_out(struct task_struct *task,
struct perf_cgroup *cgrp1;
struct perf_cgroup *cgrp2 = NULL;

+ rcu_read_lock();
/*
* we come here when we know perf_cgroup_events > 0
*/
@@ -561,6 +559,8 @@ static inline void perf_cgroup_sched_out(struct task_struct *task,
*/
if (cgrp1 != cgrp2)
perf_cgroup_switch(task, PERF_CGROUP_SWOUT);
+
+ rcu_read_unlock();
}

static inline void perf_cgroup_sched_in(struct task_struct *prev,
@@ -569,6 +569,7 @@ static inline void perf_cgroup_sched_in(struct task_struct *prev,
struct perf_cgroup *cgrp1;
struct perf_cgroup *cgrp2 = NULL;

+ rcu_read_lock();
/*
* we come here when we know perf_cgroup_events > 0
*/
@@ -584,6 +585,8 @@ static inline void perf_cgroup_sched_in(struct task_struct *prev,
*/
if (cgrp1 != cgrp2)
perf_cgroup_switch(task, PERF_CGROUP_SWIN);
+
+ rcu_read_unlock();
}

static inline int perf_cgroup_connect(int fd, struct perf_event *event,
@@ -9447,7 +9450,9 @@ static void perf_cgroup_css_free(struct cgroup_subsys_state *css)
static int __perf_cgroup_move(void *info)
{
struct task_struct *task = info;
+ rcu_read_lock();
perf_cgroup_switch(task, PERF_CGROUP_SWOUT | PERF_CGROUP_SWIN);
+ rcu_read_unlock();
return 0;
}

--
2.5.0


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