Re: [PATCH v3] perf: fix RCU issues with cgroup monitoring mode

[kbuild test robot]

Hi Stephane,

[auto build test WARNING on: tip/perf/core]
[also build test WARNING on: v4.3 next-20151103]

url:    https://github.com/0day-ci/linux/commits/Stephane-Eranian/perf-fix-RCU-issues-with-cgroup-monitoring-mode/20151104-121512
config: i386-randconfig-i0-201544 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All warnings (new ones prefixed by >>):

   In file included from include/linux/trace_events.h:9:0,
                    from include/trace/syscall.h:6,
                    from include/linux/syscalls.h:81,
                    from init/main.c:18:
   include/linux/perf_event.h: In function 'perf_cgroup_from_task':
>> include/linux/perf_event.h:702:7: warning: unused variable 'safe' [-Wunused-variable]
     bool safe = ctx ? lockdep_is_held(&ctx->lock) : true;
          ^

vim +/safe +702 include/linux/perf_event.h

   686		u64				timestamp;
   687	};
   688	
   689	struct perf_cgroup {
   690		struct cgroup_subsys_state	css;
   691		struct perf_cgroup_info	__percpu *info;
   692	};
   693	
   694	/*
   695	 * Must ensure cgroup is pinned (css_get) before calling
   696	 * this function. In other words, we cannot call this function
   697	 * if there is no cgroup event for the current CPU context.
   698	 */
   699	static inline struct perf_cgroup *
   700	perf_cgroup_from_task(struct task_struct *task, struct perf_event_context *ctx)
   701	{
 > 702		bool safe = ctx ? lockdep_is_held(&ctx->lock) : true;
   703		return container_of(task_css_check(task, perf_event_cgrp_id, safe),
   704				    struct perf_cgroup, css);
   705	}
   706	#endif /* CONFIG_CGROUP_PERF */
   707	
   708	#ifdef CONFIG_PERF_EVENTS
   709	
   710	extern void *perf_aux_output_begin(struct perf_output_handle *handle,

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