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Message-ID: <20151104041219.GA12969@thinkpad>
Date: Wed, 4 Nov 2015 05:12:19 +0100
From: Stephane Eranian <eranian@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: peterz@...radead.org, mingo@...e.hu, ak@...ux.intel.com,
edumazet@...gle.com, acme@...hat.com
Subject: [PATCH v3] perf: fix RCU issues with cgroup monitoring mode
This patch eliminates RCU violations detected by the RCU
checker (PROVE_RCU). The impact code paths were all related
to cgroup mode monitoring and involved access a task's cgrp.
V2 is updated to include comments from PeterZ to eliminate
some of the warnings without grabbing the rcu_read lock because
we know we are already holding th ctx->lock which prevents
the cgroup from disappearing while we are accessing it.
The trick, as suggested by Peter, is to modify the
perf_cgroup_from_task() to take an extra boolean parameter
to allow bypassing the lockdep test in the task_subsys_cstate()
macros. This patch uses this approach to update all calls the
perf_cgroup_from_task().
In V3, we change the boolean parameter for a pointer to a
perf_event_context so we can check the ctx->lock explicitely.
This is more robust, than passing the boolean to express that
we know the lock is held. The code can change, and thus the
locking assumption, checking lockdep_is_held() ensures,
the proper locking is in place. Patch relative to tip.git
at commit 57ef9fc.
Signed-off-by: Stephane Eranian <eranian@...gle.com>
---
arch/x86/kernel/cpu/perf_event_intel_cqm.c | 2 +-
include/linux/perf_event.h | 5 +++--
kernel/events/core.c | 25 +++++++++++++++----------
3 files changed, 19 insertions(+), 13 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event_intel_cqm.c b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
index 377e8f8..a316ca9 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_cqm.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
@@ -298,7 +298,7 @@ static bool __match_event(struct perf_event *a, struct perf_event *b)
static inline struct perf_cgroup *event_to_cgroup(struct perf_event *event)
{
if (event->attach_state & PERF_ATTACH_TASK)
- return perf_cgroup_from_task(event->hw.target);
+ return perf_cgroup_from_task(event->hw.target, event->ctx);
return event->cgrp;
}
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index d841d33..94107e4 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -697,9 +697,10 @@ struct perf_cgroup {
* if there is no cgroup event for the current CPU context.
*/
static inline struct perf_cgroup *
-perf_cgroup_from_task(struct task_struct *task)
+perf_cgroup_from_task(struct task_struct *task, struct perf_event_context *ctx)
{
- return container_of(task_css(task, perf_event_cgrp_id),
+ bool safe = ctx ? lockdep_is_held(&ctx->lock) : true;
+ return container_of(task_css_check(task, perf_event_cgrp_id, safe),
struct perf_cgroup, css);
}
#endif /* CONFIG_CGROUP_PERF */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index ea02109..f611246 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -435,7 +435,7 @@ static inline void update_cgrp_time_from_event(struct perf_event *event)
if (!is_cgroup_event(event))
return;
- cgrp = perf_cgroup_from_task(current);
+ cgrp = perf_cgroup_from_task(current, event->ctx);
/*
* Do not update time when cgroup is not active
*/
@@ -458,7 +458,7 @@ perf_cgroup_set_timestamp(struct task_struct *task,
if (!task || !ctx->nr_cgroups)
return;
- cgrp = perf_cgroup_from_task(task);
+ cgrp = perf_cgroup_from_task(task, ctx);
info = this_cpu_ptr(cgrp->info);
info->timestamp = ctx->timestamp;
}
@@ -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);
@@ -523,7 +522,7 @@ static void perf_cgroup_switch(struct task_struct *task, int mode)
* event_filter_match() to not have to pass
* task around
*/
- cpuctx->cgrp = perf_cgroup_from_task(task);
+ cpuctx->cgrp = perf_cgroup_from_task(task, NULL);
cpu_ctx_sched_in(cpuctx, EVENT_ALL, task);
}
perf_pmu_enable(cpuctx->ctx.pmu);
@@ -531,8 +530,6 @@ static void perf_cgroup_switch(struct task_struct *task, int mode)
}
}
- rcu_read_unlock();
-
local_irq_restore(flags);
}
@@ -542,17 +539,18 @@ 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
*/
- cgrp1 = perf_cgroup_from_task(task);
+ cgrp1 = perf_cgroup_from_task(task, NULL);
/*
* next is NULL when called from perf_event_enable_on_exec()
* that will systematically cause a cgroup_switch()
*/
if (next)
- cgrp2 = perf_cgroup_from_task(next);
+ cgrp2 = perf_cgroup_from_task(next, NULL);
/*
* only schedule out current cgroup events if we know
@@ -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,
@@ -569,13 +569,14 @@ 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
*/
- cgrp1 = perf_cgroup_from_task(task);
+ cgrp1 = perf_cgroup_from_task(task, NULL);
/* prev can never be NULL */
- cgrp2 = perf_cgroup_from_task(prev);
+ cgrp2 = perf_cgroup_from_task(prev, NULL);
/*
* only need to schedule in cgroup events if we are changing
@@ -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,
@@ -9442,7 +9445,9 @@ 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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