Commit d3296fb3 authored by Jiri Olsa's avatar Jiri Olsa Committed by Ingo Molnar
Browse files

perf/core: Disable page faults when getting phys address 



We hit following warning when running tests on kernel
compiled with CONFIG_DEBUG_ATOMIC_SLEEP=y:

 WARNING: CPU: 19 PID: 4472 at mm/gup.c:2381 __get_user_pages_fast+0x1a4/0x200
 CPU: 19 PID: 4472 Comm: dummy Not tainted 5.6.0-rc6+ #3
 RIP: 0010:__get_user_pages_fast+0x1a4/0x200
 ...
 Call Trace:
  perf_prepare_sample+0xff1/0x1d90
  perf_event_output_forward+0xe8/0x210
  __perf_event_overflow+0x11a/0x310
  __intel_pmu_pebs_event+0x657/0x850
  intel_pmu_drain_pebs_nhm+0x7de/0x11d0
  handle_pmi_common+0x1b2/0x650
  intel_pmu_handle_irq+0x17b/0x370
  perf_event_nmi_handler+0x40/0x60
  nmi_handle+0x192/0x590
  default_do_nmi+0x6d/0x150
  do_nmi+0x2f9/0x3c0
  nmi+0x8e/0xd7

While __get_user_pages_fast() is IRQ-safe, it calls access_ok(),
which warns on:

  WARN_ON_ONCE(!in_task() && !pagefault_disabled())

Peter suggested disabling page faults around __get_user_pages_fast(),
which gets rid of the warning in access_ok() call.

Suggested-by: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20200407141427.3184722-1-jolsa@kernel.org
parent 2b3b76b5

kernel/events/core.c

+6 −3
Original line number Diff line number Diff line
@@ -6934,9 +6934,12 @@ static u64 perf_virt_to_phys(u64 virt) 
		 * Try IRQ-safe __get_user_pages_fast first.

		 * If failed, leave phys_addr as 0.

		 */

		if ((current->mm != NULL) &&

		    (__get_user_pages_fast(virt, 1, 0, &p) == 1))

		if (current->mm != NULL) {

			pagefault_disable();

			if (__get_user_pages_fast(virt, 1, 0, &p) == 1)

				phys_addr = page_to_phys(p) + virt % PAGE_SIZE;

			pagefault_enable();

		}



		if (p)

			put_page(p);