Commit a96bbc16 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

perf_counter: Fix race in counter initialization 



We need the PID namespace and counter ID available when the
counter overflows and we need to generate a sample event.

[ Impact: fix kernel crash with high-frequency sampling ]

Reported-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <new-submission>
[ fixed a further crash and cleaned up the initialization a bit ]
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 8229289b

kernel/perf_counter.c

+14 −11
Original line number Diff line number Diff line
@@ -48,6 +48,8 @@ int sysctl_perf_counter_priv __read_mostly; /* do we need to be privileged */ 
int sysctl_perf_counter_mlock __read_mostly = 512; /* 'free' kb per user */

int sysctl_perf_counter_limit __read_mostly = 100000; /* max NMIs per second */



static atomic64_t perf_counter_id;



/*

 * Lock for (sysadmin-configurable) counter reservations:

 */
@@ -3358,7 +3360,11 @@ perf_counter_alloc(struct perf_counter_attr *attr, 
	counter->ctx		= ctx;

	counter->oncpu		= -1;



	counter->ns		= get_pid_ns(current->nsproxy->pid_ns);

	counter->id		= atomic64_inc_return(&perf_counter_id);



	counter->state		= PERF_COUNTER_STATE_INACTIVE;



	if (attr->disabled)

		counter->state = PERF_COUNTER_STATE_OFF;
@@ -3402,6 +3408,8 @@ done: 
		err = PTR_ERR(pmu);



	if (err) {

		if (counter->ns)

			put_pid_ns(counter->ns);

		kfree(counter);

		return ERR_PTR(err);

	}
@@ -3419,8 +3427,6 @@ done: 
	return counter;

}



static atomic64_t perf_counter_id;



/**

 * sys_perf_counter_open - open a performance counter, associate it to a task/cpu

 *
@@ -3515,9 +3521,6 @@ SYSCALL_DEFINE5(perf_counter_open, 
	list_add_tail(&counter->owner_entry, &current->perf_counter_list);

	mutex_unlock(&current->perf_counter_mutex);



	counter->ns = get_pid_ns(current->nsproxy->pid_ns);

	counter->id = atomic64_inc_return(&perf_counter_id);



	fput_light(counter_file, fput_needed2);



out_fput:

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