uprobes: Fix the waitqueue_active() check in xol_free_insn_slot()
uprobes: Fix the waitqueue_active() check in xol_free_insn_slot()

The xol_free_insn_slot()->waitqueue_active() check is buggy. We
need mb() after we set the conditon for wait_event(), or
xol_take_insn_slot() can miss the wakeup.

Signed-off-by: Oleg Nesterov <20b70f0af00562e63758b9ee42012ecc96c58590@redhat.com>
Cc: Andy Lutomirski <2cc0d0d76de2e6f37b92deeb83c85cb306fc5dc1@amacapital.net>
Cc: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>
Cc: Peter Zijlstra <3fddac958924aef220f202ca567388ddab3f14a8@infradead.org>
Cc: Pratyush Anand <d87ec5d367317dddadb0e3ae3e592b2c0573cf36@redhat.com>
Cc: Srikar Dronamraju <1f69195f6d934d4caf5816234bde319316df237e@linux.vnet.ibm.com>
Cc: Thomas Gleixner <00e4cf8f46a57000a44449bf9dd8cbbcc209fd2a@linutronix.de>
Link: 4bd50206b528c783a4daede3bcbd5b54c045bdc9@redhat.com
Signed-off-by: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@kernel.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs