Commit 5aab90ce authored Oct 26, 2016 by Jiri Olsa Committed by Ingo Molnar Oct 28, 2016

perf/powerpc: Don't call perf_event_disable() from atomic context



The trinity syscall fuzzer triggered following WARN() on powerpc:

  WARNING: CPU: 9 PID: 2998 at arch/powerpc/kernel/hw_breakpoint.c:278
  ...
  NIP [c00000000093aedc] .hw_breakpoint_handler+0x28c/0x2b0
  LR [c00000000093aed8] .hw_breakpoint_handler+0x288/0x2b0
  Call Trace:
  [c0000002f7933580] [c00000000093aed8] .hw_breakpoint_handler+0x288/0x2b0 (unreliable)
  [c0000002f7933630] [c0000000000f671c] .notifier_call_chain+0x7c/0xf0
  [c0000002f79336d0] [c0000000000f6abc] .__atomic_notifier_call_chain+0xbc/0x1c0
  [c0000002f7933780] [c0000000000f6c40] .notify_die+0x70/0xd0
  [c0000002f7933820] [c00000000001a74c] .do_break+0x4c/0x100
  [c0000002f7933920] [c0000000000089fc] handle_dabr_fault+0x14/0x48

Followed by a lockdep warning:

  ===============================
  [ INFO: suspicious RCU usage. ]
  4.8.0-rc5+ #7 Tainted: G        W
  -------------------------------
  ./include/linux/rcupdate.h:556 Illegal context switch in RCU read-side critical section!

  other info that might help us debug this:

  rcu_scheduler_active = 1, debug_locks = 0
  2 locks held by ls/2998:
   #0:  (rcu_read_lock){......}, at: [<c0000000000f6a00>] .__atomic_notifier_call_chain+0x0/0x1c0
   #1:  (rcu_read_lock){......}, at: [<c00000000093ac50>] .hw_breakpoint_handler+0x0/0x2b0

  stack backtrace:
  CPU: 9 PID: 2998 Comm: ls Tainted: G        W       4.8.0-rc5+ #7
  Call Trace:
  [c0000002f7933150] [c00000000094b1f8] .dump_stack+0xe0/0x14c (unreliable)
  [c0000002f79331e0] [c00000000013c468] .lockdep_rcu_suspicious+0x138/0x180
  [c0000002f7933270] [c0000000001005d8] .___might_sleep+0x278/0x2e0
  [c0000002f7933300] [c000000000935584] .mutex_lock_nested+0x64/0x5a0
  [c0000002f7933410] [c00000000023084c] .perf_event_ctx_lock_nested+0x16c/0x380
  [c0000002f7933500] [c000000000230a80] .perf_event_disable+0x20/0x60
  [c0000002f7933580] [c00000000093aeec] .hw_breakpoint_handler+0x29c/0x2b0
  [c0000002f7933630] [c0000000000f671c] .notifier_call_chain+0x7c/0xf0
  [c0000002f79336d0] [c0000000000f6abc] .__atomic_notifier_call_chain+0xbc/0x1c0
  [c0000002f7933780] [c0000000000f6c40] .notify_die+0x70/0xd0
  [c0000002f7933820] [c00000000001a74c] .do_break+0x4c/0x100
  [c0000002f7933920] [c0000000000089fc] handle_dabr_fault+0x14/0x48

While it looks like the first WARN() is probably valid, the other one is
triggered by disabling event via perf_event_disable() from atomic context.

The event is disabled here in case we were not able to emulate
the instruction that hit the breakpoint. By disabling the event
we unschedule the event and make sure it's not scheduled back.

But we can't call perf_event_disable() from atomic context, instead
we need to use the event's pending_disable irq_work method to disable it.

Reported-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20161026094824.GA21397@krava


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 0933840a

arch/powerpc/kernel/hw_breakpoint.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -275,7 +275,7 @@ int hw_breakpoint_handler(struct die_args *args)
		if (!stepped) {
		WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
		"0x%lx will be disabled.", info->address);
		perf_event_disable(bp);
		perf_event_disable_inatomic(bp);
		goto out;
		}
		/*

include/linux/perf_event.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -1257,6 +1257,7 @@ extern u64 perf_swevent_set_period(struct perf_event *event);
		extern void perf_event_enable(struct perf_event *event);
		extern void perf_event_disable(struct perf_event *event);
		extern void perf_event_disable_local(struct perf_event *event);
		extern void perf_event_disable_inatomic(struct perf_event *event);
		extern void perf_event_task_tick(void);
		#else /* !CONFIG_PERF_EVENTS: */
		static inline void *

kernel/events/core.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -1960,6 +1960,12 @@ void perf_event_disable(struct perf_event *event)
		}
		EXPORT_SYMBOL_GPL(perf_event_disable);

		void perf_event_disable_inatomic(struct perf_event *event)
		{
		event->pending_disable = 1;
		irq_work_queue(&event->pending);
		}

		static void perf_set_shadow_time(struct perf_event *event,
		struct perf_event_context *ctx,
		u64 tstamp)
		@@ -7075,8 +7081,8 @@ static int __perf_event_overflow(struct perf_event *event,
		if (events && atomic_dec_and_test(&event->event_limit)) {
		ret = 1;
		event->pending_kill = POLL_HUP;
		event->pending_disable = 1;
		irq_work_queue(&event->pending);

		perf_event_disable_inatomic(event);
		}

		READ_ONCE(event->overflow_handler)(event, data, regs);

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