From 8b6a3fe8fab97716990a3abde1a01fb5a34552a3 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Wed, 24 Aug 2016 10:07:14 +0100 Subject: perf/core: Use this_cpu_ptr() when stopping AUX events When tearing down an AUX buf for an event via perf_mmap_close(), __perf_event_output_stop() is called on the event's CPU to ensure that trace generation is halted before the process of unmapping and freeing the buffer pages begins. The callback is performed via cpu_function_call(), which ensures that it runs with interrupts disabled and is therefore not preemptible. Unfortunately, the current code grabs the per-cpu context pointer using get_cpu_ptr(), which unnecessarily disables preemption and doesn't pair the call with put_cpu_ptr(), leading to a preempt_count() imbalance and a BUG when freeing the AUX buffer later on: WARNING: CPU: 1 PID: 2249 at kernel/events/ring_buffer.c:539 __rb_free_aux+0x10c/0x120 Modules linked in: [...] Call Trace: [] dump_stack+0x4f/0x72 [] __warn+0xc6/0xe0 [] warn_slowpath_null+0x18/0x20 [] __rb_free_aux+0x10c/0x120 [] rb_free_aux+0x13/0x20 [] perf_mmap_close+0x29e/0x2f0 [] ? perf_iterate_ctx+0xe0/0xe0 [] remove_vma+0x25/0x60 [] exit_mmap+0x106/0x140 [] mmput+0x1c/0xd0 [] do_exit+0x253/0xbf0 [] do_group_exit+0x3e/0xb0 [] get_signal+0x249/0x640 [] do_signal+0x23/0x640 [] ? _raw_write_unlock_irq+0x12/0x30 [] ? _raw_spin_unlock_irq+0x9/0x10 [] ? __schedule+0x2c6/0x710 [] exit_to_usermode_loop+0x74/0x90 [] prepare_exit_to_usermode+0x26/0x30 [] retint_user+0x8/0x10 This patch uses this_cpu_ptr() instead of get_cpu_ptr(), since preemption is already disabled by the caller. Signed-off-by: Will Deacon Reviewed-by: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Vince Weaver Fixes: 95ff4ca26c49 ("perf/core: Free AUX pages in unmap path") Link: http://lkml.kernel.org/r/20160824091905.GA16944@arm.com Signed-off-by: Ingo Molnar --- kernel/events/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/events') diff --git a/kernel/events/core.c b/kernel/events/core.c index 5650f5317e0c..3cfabdf7b942 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6166,7 +6166,7 @@ static int __perf_pmu_output_stop(void *info) { struct perf_event *event = info; struct pmu *pmu = event->pmu; - struct perf_cpu_context *cpuctx = get_cpu_ptr(pmu->pmu_cpu_context); + struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context); struct remote_output ro = { .rb = event->rb, }; -- cgit v1.2.3 From 58763148758057ffc447bf990321d3ea86d199a0 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 30 Aug 2016 10:15:03 +0200 Subject: perf/core: Remove WARN from perf_event_read() This effectively reverts commit: 71e7bc2bab77 ("perf/core: Check return value of the perf_event_read() IPI") ... and puts in a comment explaining why we ignore the return value. Reported-by: Vegard Nossum Signed-off-by: Peter Zijlstra (Intel) Cc: David Carrillo-Cisneros Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: 71e7bc2bab77 ("perf/core: Check return value of the perf_event_read() IPI") Signed-off-by: Ingo Molnar --- kernel/events/core.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) (limited to 'kernel/events') diff --git a/kernel/events/core.c b/kernel/events/core.c index 3cfabdf7b942..07ac8596a728 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -3549,10 +3549,18 @@ static int perf_event_read(struct perf_event *event, bool group) .group = group, .ret = 0, }; - ret = smp_call_function_single(event->oncpu, __perf_event_read, &data, 1); - /* The event must have been read from an online CPU: */ - WARN_ON_ONCE(ret); - ret = ret ? : data.ret; + /* + * Purposely ignore the smp_call_function_single() return + * value. + * + * If event->oncpu isn't a valid CPU it means the event got + * scheduled out and that will have updated the event count. + * + * Therefore, either way, we'll have an up-to-date event count + * after this. + */ + (void)smp_call_function_single(event->oncpu, __perf_event_read, &data, 1); + ret = data.ret; } else if (event->state == PERF_EVENT_STATE_INACTIVE) { struct perf_event_context *ctx = event->ctx; unsigned long flags; -- cgit v1.2.3