id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	field_blocks	field_dependson	field_seealso
231	Two CPUs in critical section under Qemu/ia32/SMP	Jakub Jermář	Jakub Jermář	"After applying the attached changes on top of changeset:mainline,377, I am observing (under Qemu 0.11.?, 0.12.2+3) what appears to be more than one CPU in a spinlock-protected critical section.

In order to figure out more, I improved the spinlock code to be more sensitive to random lock corruption (which I can thus rule out) and also to be more observable by providing a global ring buffer for recording the locking history. See the attachement to see the diff. I am also going to attach screenshots which illustrate the panics.

Frankly speaking, my suspect number one is actually Qemu (since the HelenOS code looks good to me atm.), but I am logging this ticket anyway just for the case I am wrong. One more thing which makes me think that this is rather a Qemu issue is that with the given ring buffer and the spinlock_lock_debug() code, I would expect the panic to occur in spinlock_lock_debug() on either of the two checks for multiple CPUs in the CS, and not so late in spinlock_unlock(). With this behavior, the simulated CPUs appear to use some very strange memory model (i.e. we observe the effect of the lock_event_record() on both CPUs that manage to ""lock"" the spinlock, but in most of the cases do not hit the ""not alone in critical section"" panic)."	defect	closed	major	0.6.0	helenos/kernel/ia32	mainline	deferred