[PATCH 0/2] cleanup: Conditional locking support

[Peter Zijlstra]

Hi,

Two patches, the first extending the cleanup/guard stuff to better handle
conditional locks, mutex_trylock(), mutex_lock_interruptible() etc.. And the
second a small ptrace conversion that I've been using as a test-case.

The normal scoped_guard() is changed to simply skip the body when a conditional
lock fails to acquire. A new scoped_cond_guard() is added that takes an extra
statement argument to provide an explicit 'fail' action.

The ptrace patch has:

  scoped_cond_guard (mutex_intr, return -ERESTARTNOINTR,
		     &task->signal->cred_guard_mutex) {
    ...
  }
  ...
  return 0;

Where if the lock acquire fails, it does 'return -ERESTARTNOINTR'.

The crazy perf thing then becomes:

  scoped_cond_guard (rwsem_read_intr, goto no_lock,
                     task ? &task->signal->exec_update_lock : NULL) {
    if (0) {
no_lock:
      if (task)
        return -EINTR;
    }
    ... body with or without lock ...
  }


Specifically, that thing needs the lock when there is a task, but otherwise
needs to still do the body without the lock.

IIO also wanted something along these lines, although they have a custom
'trylock' thing.

Barring objections, I'm planning to merge this into tip/locking/cleanup which
I'll merge into tip/locking/core (and tip/perf/core when times comes).

My plan is to post the perf patches in 3 batches of roughly 10 patches each,
the simpler first and the more crazy ones (including the above) last.