From: Jiri Olsa jolsa@kernel.org
[ Upstream commit d3296fb372bf7497b0e5d0478c4e7a677ec6f6e9 ]
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 peterz@infradead.org Signed-off-by: Jiri Olsa jolsa@kernel.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Ingo Molnar mingo@kernel.org Link: https://lkml.kernel.org/r/20200407141427.3184722-1-jolsa@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/events/core.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c index 243717177f446..533c193481899 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6734,9 +6734,12 @@ 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)) - phys_addr = page_to_phys(p) + virt % PAGE_SIZE; + 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);