Currently it discards a lock_stat for a lock instance when there's a
broken lock_seq_stat in a single task for the lock.  But it also means
that the existing (and later) valid lock stat info for that lock will
be discarded as well.

This is not ideal since we can lose many valuable info because of a
single failure.  Actually those failures are indepent to the existing
stat.  So we can only discard the broken lock_seq_stat but keep the
valid lock_stat.

The discarded lock_seq_stat will be reallocated in a subsequent event
with SEQ_STATE_UNINITIALIZED which will be ignored until it see the
start of the next sequence.  So it should be ok just free it.

Before:

  $ perf lock report -F acquired,contended,avg_wait

  Warning:
  Processed 1401603 events and lost 18 chunks!

  Check IO/CPU overload!

                  Name   acquired  contended   avg wait (ns)

         rcu_read_lock     251225          0               0
   &(ei->i_block_re...       8731          0               0
   &sb->s_type->i_l...       8731          0               0
    hrtimer_bases.lock       5261          0               0
    hrtimer_bases.lock       2626          0               0
    hrtimer_bases.lock       1953          0               0
    hrtimer_bases.lock       1382          0               0
      cpu_hotplug_lock       1350          0               0
    hrtimer_bases.lock       1273          0               0
    hrtimer_bases.lock       1269          0               0
    hrtimer_bases.lock       1198          0               0
   ...

New:
                  Name   acquired  contended   avg wait (ns)

         rcu_read_lock     251225          0               0
   tk_core.seq.seqc...      54074          0               0
          &xa->xa_lock      17470          0               0
        &ei->i_es_lock      17464          0               0
       &ei->i_raw_lock       9391          0               0
   &mapping->privat...       8734          0               0
       &ei->i_data_sem       8731          0               0
   &(ei->i_block_re...       8731          0               0
   &sb->s_type->i_l...       8731          0               0
   jiffies_seq.seqc...       6953          0               0
        &mm->mmap_lock       6889          0               0
             balancing       5768          0               0
    hrtimer_bases.lock       5261          0               0
   ...
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220521010811.932703-1-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>