It turns out that there are BPF use cases that rely on nesting RCU
Tasks Trace readers. These use cases are well-served by the old
rcu_read_lock_trace() and rcu_read_unlock_trace() functions that maintain
a nesting counter in the task_struct structure. But these use cases incur
a performance penalty when using the shiny new rcu_read_lock_tasks_trace()
and rcu_read_unlock_tasks_trace() functions, which nest in the same way
that SRCU does.
This means that rcu_read_lock_trace() and rcu_read_unlock_trace()
will be with us for some time. Therefore, remove the checkpatch.pl
deprecation.
Also, the rcu_read_lock_tasks_trace() and rcu_read_unlock_tasks_trace()
functions are intended for use only by BPF. Therefore, add them to
the list of functions that checkpatch complains about outside of BPF
(and of course, RCU).
Reported-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Joe Perches <joe@perches.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Paul E. McKenney
012c889690