130c5ce716
This fixes the A->B/B->A locking dependency, see the warning below.
The function task_exit_notify() is called with (task_exit_notifier)
.rwsem set and then calls sync_buffer() which locks buffer_mutex. In
sync_start() the buffer_mutex was set to prevent notifier functions to
be started before sync_start() is finished. But when registering the
notifier, (task_exit_notifier).rwsem is locked too, but now in
different order than in sync_buffer(). In theory this causes a locking
dependency, what does not occur in practice since task_exit_notify()
is always called after the notifier is registered which means the lock
is already released.
However, after checking the notifier functions it turned out the
buffer_mutex in sync_start() is unnecessary. This is because
sync_buffer() may be called from the notifiers even if sync_start()
did not finish yet, the buffers are already allocated but empty. No
need to protect this with the mutex.
So we fix this theoretical locking dependency by removing buffer_mutex
in sync_start(). This is similar to the implementation before commit:
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.. | ||
buffer_sync.c | ||
buffer_sync.h | ||
cpu_buffer.c | ||
cpu_buffer.h | ||
event_buffer.c | ||
event_buffer.h | ||
oprof.c | ||
oprof.h | ||
oprofile_files.c | ||
oprofile_perf.c | ||
oprofile_stats.c | ||
oprofile_stats.h | ||
oprofilefs.c | ||
timer_int.c |