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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: Peter Zijlstra <[email protected]> Signed-off-by: Jiri Olsa <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Signed-off-by: Ingo Molnar <[email protected]> Link: https://lkml.kernel.org/r/[email protected]
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