ipc/msg: lockless security checks for msgsnd

ipc/msg: lockless security checks for msgsnd

Just as with msgrcv (along with the rest of sysvipc since a few years
ago), perform the security checks without holding the ipc object lock.
This also reduces the hogging of the lock for the entire duration of a
sender, as we drop the lock upon every iteration -- and this is exactly
why we also check for racing with RMID in the first place.

Link: http://lkml.kernel.org/r/1469748819-19484-5-git-send-email-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>