perf events: Clean up pid passing

perf events: Clean up pid passing

The kernel perf event creation path shouldn't use find_task_by_vpid()
because a vpid exists in a specific namespace. find_task_by_vpid() uses
current's pid namespace which isn't always the correct namespace to use
for the vpid in all the places perf_event_create_kernel_counter() (and
thus find_get_context()) is called.

The goal is to clean up pid namespace handling and prevent bugs like:

	https://bugzilla.kernel.org/show_bug.cgi?id=17281

Instead of using pids switch find_get_context() to use task struct
pointers directly. The syscall is responsible for resolving the pid to
a task struct. This moves the pid namespace resolution into the syscall
much like every other syscall that takes pid parameters.

Signed-off-by: Matt Helsley <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Cc: Robin Green <[email protected]>
Cc: Prasad <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Mahesh Salgaonkar <[email protected]>
LKML-Reference: <a134e5e392ab0204961fd1a62c84a222bf5874a9.1284407763[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>