On Thu, 8 Jan 2009, Steven Rostedt wrote: > > We keep spinning if the owner changes. I think we want to - if you have multiple CPU's and a heavily contended lock that acts as a spinlock, we still _do_ want to keep spinning even if another CPU gets the lock. And I don't even believe that is the bug. I suspect the bug is simpler. I think the "need_resched()" needs to go in the outer loop, or at least happen in the "!owner" case. Because at least with preemption, what can happen otherwise is - process A gets the lock, but gets preempted before it sets lock->owner. End result: count = 0, owner = NULL. - processes B/C goes into the spin loop, filling up all CPU's (assuming dual-core here), and will now both loop forever if they hold the kernel lock (or have some other preemption disabling thing over their down()). And all the while, process A would _happily_ set ->owner, and eventually release the mutex, but it never gets to run to do either of them so. In fact, you might not even need a process C: all you need is for B to be on the same runqueue as A, and having enough load on the other CPU's that A never gets migrated away. So "C" might be in user space. I dunno. There are probably variations on the above. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
