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Re: mutexes, locks and so on...

On 11/17/10 05:15, Matt Thomas wrote:

On Nov 16, 2010, at 8:04 PM, Johnny Billquist wrote:

On 2010-11-17 04:52, Matt Thomas wrote:

Not true.  Spinlocks must enter through mutex_spin_enter and adaptive mutexes
enter through mutex_enter.  The corresponding is true for exiting as well.
The only reason mutex_vector_{enter,exit} is called to cause a panic.

That may be true in theory, but I happen to know (now) that it's not true in 
reality. I've found atleast one place in the kernel where this is done.

Then that is a bug and should be fixed.  File a PR.

Ouch. Should I also file bugs for mutexes that are released, but already appear to be free? Because that also happens.

I actually wonder if it is a bug, or just a chosen design. I'd rather say we should get rid of the mutex_spin_{} functions, since the kernel is so confused about the whole thing anyway.

I'm adding a bunch of counters now, and will come back with how often these things are abused in a minute...

Oh, and mutex_vector_exit will not cause a panic, just because it was called 
from mmutex_spin_exit with a adaptive mutex. mutex_vector_exit will simply just 
handle it as an adaptive mutex, and release it.

That should probably be fixed.

How? mutex_vector_{enter,exit} have been written to handle both spin and adaptive mutexes. And it don't know that it might have been called from mutex_spin_{} with an adaptive mutex. It might in fact be the only function available for both kinds... You don't have to write your own mutex_[]_{enter,exit} functions, and if not, the mutex_vector ones will be used directly.


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