[RFC 0/6] uprobes: kill uprobes_srcu/uprobe_srcu_id

[Oleg Nesterov <oleg@redhat.com>]

Hello.

Not for inclusion yet, only for the early review.

I didn't even try to test these changes, and I am not expert
in this area. And even _if_ this code is correct, I need to
re-split these changes anyway, update the changelogs, etc.

Questions:

	- does it make sense?

	- can it work or I missed something "in general" ?

Why:

	- It would be nice to remove a member from task_struct.

	- Afaics, the usage of uprobes_srcu does not look right,
	  at least in theory, see 6/6.

	  The comment above delete_uprobe() says:

	  	The current unregistering thread waits till all
	  	other threads have hit a breakpoint, to acquire
	  	the uprobes_treelock before the uprobe is removed
	  	from the rbtree.

	  but synchronize_srcu() can only help if a thread which
	  have hit the breakpoint has already called srcu_read_lock().
	  It can't synchronize with read_lock "in future", and there
	  is a small window.

	  We could probably add another synchronize_sched() before
	  synchronize_srcu(), but this doesn't look very nice and

	- I am not sure yet, but perhaps with these changes we can
	  also kill mm->uprobes_state.count.

Any review is very much appreciated.

Oleg.

 include/linux/sched.h   |    1 -
 kernel/events/uprobes.c |  117 ++++++++++++++++++++++++++++++-----------------
 2 files changed, 75 insertions(+), 43 deletions(-)