linux/kernel/events
Song Liu f792565326 perf/core: fix userpage->time_enabled of inactive events
Users of rdpmc rely on the mmapped user page to calculate accurate
time_enabled. Currently, userpage->time_enabled is only updated when the
event is added to the pmu. As a result, inactive event (due to counter
multiplexing) does not have accurate userpage->time_enabled. This can
be reproduced with something like:

   /* open 20 task perf_event "cycles", to create multiplexing */

   fd = perf_event_open();  /* open task perf_event "cycles" */
   userpage = mmap(fd);     /* use mmap and rdmpc */

   while (true) {
     time_enabled_mmap = xxx; /* use logic in perf_event_mmap_page */
     time_enabled_read = read(fd).time_enabled;
     if (time_enabled_mmap > time_enabled_read)
         BUG();
   }

Fix this by updating userpage for inactive events in merge_sched_in.

Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reported-and-tested-by: Lucian Grijincu <lucian@fb.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210929194313.2398474-1-songliubraving@fb.com
2021-10-01 13:57:54 +02:00
..
callchain.c uaccess: add force_uaccess_{begin,end} helpers 2020-08-12 10:57:59 -07:00
core.c perf/core: fix userpage->time_enabled of inactive events 2021-10-01 13:57:54 +02:00
hw_breakpoint.c perf/hw_breakpoint: Replace deprecated CPU-hotplug functions 2021-08-26 09:14:36 +02:00
internal.h perf: Optimize get_recursion_context() 2020-11-09 18:12:34 +01:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
ring_buffer.c perf: Cap allocation order at aux_watermark 2021-04-16 16:32:39 +02:00
uprobes.c Merge branch 'akpm' (patches from Andrew) 2021-06-29 17:29:11 -07:00