svn commit: r206878 - head/sys/kern
attilio at freebsd.org
Sun May 9 22:27:42 UTC 2010
2010/5/9 Marius Strobl <marius at alchemy.franken.de>:
> On Mon, Apr 19, 2010 at 11:27:54PM +0000, Attilio Rao wrote:
>> Author: attilio
>> Date: Mon Apr 19 23:27:54 2010
>> New Revision: 206878
>> URL: http://svn.freebsd.org/changeset/base/206878
>> Fix a deadlock in the shutdown code:
>> When performing a smp_rendezvous() or more likely, on amd64 and i386,
>> a smp_tlb_shootdown() the caller will end up with the smp_ipi_mtx
>> spinlock held, busy-waiting for other CPUs to acknowledge the operation.
>> As long as CPUs are suspended (via cpu_reset()) between the active mask
>> read and IPI sending there can be a deadlock where the caller will wait
>> forever for a dead CPU to acknowledge the operation.
>> Please note that on CPU0 that is going to be someway heavier because of
>> the spinlocks being disabled earlier than quitting the machine.
>> Fix this bug by calling cpu_reset() with the smp_ipi_mtx held.
>> Note that it is very likely that a saner offline/online CPUs mechanism
>> will help heavilly in fixing similar cases as it is likely more bugs
>> of this type may arise in the future.
> This change causes a hang for me when running an SMP kernel on an
> UP machine or an MP machine with SMP disabled as in these cases
> smp_ipi_mtx isn't initialized (see mp_start()). The below patch
> fixes this for me.
thanks a lot for reporting this.
However, I think that a better fix is to always initialize the mutex.
Do you think the following patch is fine for you?:
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