On Tue, 2015-03-17 at 16:35 -0400, Steven Rostedt wrote: > On Tue, 17 Mar 2015 12:35:43 -0400 > Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > 3.10.70-rt75-rc2 stable review patch. > > If anyone has any objections, please let me know. > > > > ------------------ > > > > Here's the missing change log for this revert. I'll go back and add it > in: > > > An issue arisen that if a rt_mutex (spin_lock converted to a mutex > in PREEMPT_RT) is taken in hard interrupt context, it could cause > a false deadlock detection and trigger a BUG_ON() from the return > value of task_blocks_on_rt_mutex() in rt_spin_lock_slowlock(). > > The problem is this: > > CPU0 CPU1 > ---- ---- > spin_lock(A) > spin_lock(A) > [ blocks, but spins as owner on > CPU 0 is running ] > > <interrupt> > spin_trylock(B) > [ succeeds ] > > spin_lock(B) > <blocks> > > Now the deadlock detection triggers and follows the locking: > > Task X (on CPU0) blocked on spinlock B owned by task Y on > CPU1 (via the interrupt taking it with a try lock) > > The owner of B (Y) is blocked on spin_lock A (still spinning) > A is owned by task X (self). DEADLOCK detected! BUG_ON triggered. > > This was caused by the code to try to not raise softirq unconditionally > to allow NO_HZ_FULL to work. Unfortunately, reverting that patch causes > NO_HZ_FULL to break again, but that's still better than triggering > a BUG_ON(). (aw crap, let's go shopping)... so why is the one in timer.c ok? -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
