The following commit has been merged into the perf/urgent branch of tip:
Commit-ID: d3296fb372bf7497b0e5d0478c4e7a677ec6f6e9
Gitweb: https://git.kernel.org/tip/d3296fb372bf7497b0e5d0478c4e7a677ec6f6e9
Author: Jiri Olsa <jolsa@xxxxxxxxxx>
AuthorDate: Tue, 07 Apr 2020 16:14:27 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 08 Apr 2020 11:33:46 +02:00
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 <peterz@xxxxxxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200407141427.3184722-1-jolsa@xxxxxxxxxx
---
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 26de0a5..bc9b98a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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))
- 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);
|