Commit 5aab90ce authored by Jiri Olsa's avatar Jiri Olsa Committed by Ingo Molnar

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: default avatarJan Stancek <jstancek@redhat.com>
Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Signed-off-by: default avatarPeter 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@kravaSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 0933840a
...@@ -275,7 +275,7 @@ int hw_breakpoint_handler(struct die_args *args) ...@@ -275,7 +275,7 @@ int hw_breakpoint_handler(struct die_args *args)
if (!stepped) { if (!stepped) {
WARN(1, "Unable to handle hardware breakpoint. Breakpoint at " WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
"0x%lx will be disabled.", info->address); "0x%lx will be disabled.", info->address);
perf_event_disable(bp); perf_event_disable_inatomic(bp);
goto out; goto out;
} }
/* /*
......
...@@ -1257,6 +1257,7 @@ extern u64 perf_swevent_set_period(struct perf_event *event); ...@@ -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_enable(struct perf_event *event);
extern void perf_event_disable(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_local(struct perf_event *event);
extern void perf_event_disable_inatomic(struct perf_event *event);
extern void perf_event_task_tick(void); extern void perf_event_task_tick(void);
#else /* !CONFIG_PERF_EVENTS: */ #else /* !CONFIG_PERF_EVENTS: */
static inline void * static inline void *
......
...@@ -1960,6 +1960,12 @@ void perf_event_disable(struct perf_event *event) ...@@ -1960,6 +1960,12 @@ void perf_event_disable(struct perf_event *event)
} }
EXPORT_SYMBOL_GPL(perf_event_disable); 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, static void perf_set_shadow_time(struct perf_event *event,
struct perf_event_context *ctx, struct perf_event_context *ctx,
u64 tstamp) u64 tstamp)
...@@ -7075,8 +7081,8 @@ static int __perf_event_overflow(struct perf_event *event, ...@@ -7075,8 +7081,8 @@ static int __perf_event_overflow(struct perf_event *event,
if (events && atomic_dec_and_test(&event->event_limit)) { if (events && atomic_dec_and_test(&event->event_limit)) {
ret = 1; ret = 1;
event->pending_kill = POLL_HUP; 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); READ_ONCE(event->overflow_handler)(event, data, regs);
......
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