perf lock contention: Trim backtrace by skipping traceiter functions

The 'perf lock contention' program currently shows the caller of the locks
as __traceiter_contention_begin+0x??. This caller can be ignored, as it is
from the traceiter itself. Instead, it should show the real callers for
the locks.

When fiddling with the --stack-skip parameter, the actual callers for
the locks start to show up. However, just ignore the
__traceiter_contention_begin and the __traceiter_contention_end symbols
so the actual callers will show up.

Before this patch is applied:

sudo perf lock con -a -b -- sleep 3
 contended   total wait     max wait     avg wait         type   caller

         8      2.33 s       2.28 s     291.18 ms     rwlock:W   __traceiter_contention_begin+0x44
         4      2.33 s       2.28 s     582.35 ms     rwlock:W   __traceiter_contention_begin+0x44
         7    140.30 ms     46.77 ms     20.04 ms     rwlock:W   __traceiter_contention_begin+0x44
         2     63.35 ms     33.76 ms     31.68 ms        mutex   trace_contention_begin+0x84
         2     46.74 ms     46.73 ms     23.37 ms     rwlock:W   __traceiter_contention_begin+0x44
         1     13.54 us     13.54 us     13.54 us        mutex   trace_contention_begin+0x84
         1      3.67 us      3.67 us      3.67 us      rwsem:R   __traceiter_contention_begin+0x44

Before this patch is applied - using --stack-skip 5

sudo perf lock con --stack-skip 5 -a -b -- sleep 3
 contended   total wait     max wait     avg wait         type   caller

         2      2.24 s       2.24 s       1.12 s      rwlock:W   do_epoll_wait+0x5a0
         4      1.65 s     824.21 ms    412.08 ms     rwlock:W   do_exit+0x338
         2    824.35 ms    824.29 ms    412.17 ms     spinlock   get_signal+0x108
         2    824.14 ms    824.14 ms    412.07 ms     rwlock:W   release_task+0x68
         1     25.22 ms     25.22 ms     25.22 ms        mutex   cgroup_kn_lock_live+0x58
         1     24.71 us     24.71 us     24.71 us     spinlock   do_exit+0x44
         1     22.04 us     22.04 us     22.04 us      rwsem:R   lock_mm_and_find_vma+0xb0

After this patch is applied:

sudo ./perf lock con -a -b -- sleep 3
 contended   total wait     max wait     avg wait         type   caller

         4      4.13 s       2.07 s       1.03 s      rwlock:W   release_task+0x68
         2      2.07 s       2.07 s       1.03 s      rwlock:R   mm_update_next_owner+0x50
         2      2.07 s       2.07 s       1.03 s      rwlock:W   do_exit+0x338
         1     41.56 ms     41.56 ms     41.56 ms        mutex   cgroup_kn_lock_live+0x58
         2     36.12 us     18.83 us     18.06 us     rwlock:W   do_exit+0x338

Signed-off-by: Anne Macedo <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Tested-by: Arnaldo Carvalho de Melo <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Ian Rogers <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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