Re: [Adeos-main] [BUG] ipipe_sync_stage deadlock

[Jan Kiszka <jan.kiszka@domain.hid>]

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Philippe Gerum wrote:
> Philippe Gerum wrote:
>> Jan Kiszka wrote:
>>> I love KVM - not only because I'm heavily hacking on it now, also
>>> because it is so easy to trigger various kinds of guest issues with
>>> it (SMP host + threaded virtual CPUs => true SMP guest - and if you
>>> want to watch fancy things happen, just load one host core).
>>>
>>> Here is one I found that way:
>>>
>>> void fastcall __ipipe_sync_stage(unsigned long syncmask)
>>> {
>>> [ ... ]
>>> 	while ((mask = (ipipe_this_cpudom_var(irqpend_himask) & syncmask)) != 0) {
>>> 		level = __ipipe_ffnz(mask);
>>>
>>> 		while ((submask = ipipe_this_cpudom_var(irqpend_lomask)[level]) != 0) {
>>> 			rank = __ipipe_ffnz(submask);
>>> 			irq = (level << IPIPE_IRQ_ISHIFT) + rank;
>>>
>>> 			if (test_bit(IPIPE_LOCK_FLAG, &ipd->irqs[irq].control)) {
>>> 				__clear_bit(rank, &ipipe_this_cpudom_var(irqpend_lomask)[level]);
>> - 				continue;
>> +				goto rpm_needs_more_neurons;
>>> 			}
>>>
>>> 			__clear_bit(rank, &ipipe_this_cpudom_var(irqpend_lomask)[level]);
>>>
>> + rpm_needs_more_neurons:
>>> 			if (ipipe_this_cpudom_var(irqpend_lomask)[level] == 0)
>>> 				__clear_bit(level, &ipipe_this_cpudom_var(irqpend_himask));
>>> [ ... ]
>>>
> 
> Of course, I'm not saying this is the real fix, but that just points at a
> possible issue. I do want those 100 points on my score card.

Well, I wasn't asking for a fix, just for spotting the gremlin - so you
won! :->

Then let us fix this for real:

---
 kernel/ipipe/core.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

Index: b/kernel/ipipe/core.c
===================================================================
--- a/kernel/ipipe/core.c
+++ b/kernel/ipipe/core.c
@@ -957,16 +957,14 @@ void fastcall __ipipe_sync_stage(unsigne
 			rank = __ipipe_ffnz(submask);
 			irq = (level << IPIPE_IRQ_ISHIFT) + rank;
 
-			if (test_bit(IPIPE_LOCK_FLAG, &ipd->irqs[irq].control)) {
-				__clear_bit(rank, &ipipe_this_cpudom_var(irqpend_lomask)[level]);
-				continue;
-			}
-
 			__clear_bit(rank, &ipipe_this_cpudom_var(irqpend_lomask)[level]);
 
 			if (ipipe_this_cpudom_var(irqpend_lomask)[level] == 0)
 				__clear_bit(level, &ipipe_this_cpudom_var(irqpend_himask));
 
+			if (test_bit(IPIPE_LOCK_FLAG, &ipd->irqs[irq].control))
+				continue;
+
 			__set_bit(IPIPE_STALL_FLAG, &ipipe_this_cpudom_var(status));
 
 			if (ipd == ipipe_root_domain)


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