osq_lock: avoid live-lock issue for RT task

Live Lock  due to task spinning while unqueue of CPU osq_node
from optimistic_spin_queue. Task T1 had decremented mutex count to
acquire the lock on CPU0. Before setting owner it got preempted. On
CPU1 task T2 acquired osq_lock and started spinning on owner of mutex
with preemption disabled. CPU1 runq has one task, so need_resched will
not be set. On CPU0 task T3 tried to acquire osq_lock to spin on the
same mutex. At this time following scenario causes soft lockup:

After preemption of task T1, RT task T3 tried to acquire the same
mutex. It will start spinning on the osq_lock until the lock is available
or need_resched is set. For RT task, need_resched will not be set. Task T3
will not be able to bail out of the infinite loop.

Change-Id: Ifd7506047119a22e14b15459ac6b04b410ba1c84
Signed-off-by: Prateek Sood <prsood@codeaurora.org>

0 files changed, 0 insertions, 0 deletions