Re: mutual exclusion in vkbd

From: Maksim Yevmenkin (maksim.yevmenkin_at_savvis.net)
Date: 05/31/05 

Date: Tue, 31 May 2005 13:58:59 -0700
To: Alexander Kabaev <kan@freebsd.org>

Alexander Kabaev wrote:
> On Tue, May 31, 2005 at 09:41:18AM -0700, Maksim Yevmenkin wrote:
>
>>Norbert,
>>
>>
>>>I am currently trying to backport vkbd to FreeBSD 4.
>>
>>ok
>>
>>
>>>Maksim Yevmenkin uses mtx_lock()/mtx_unlock() for
>>>protecting access to data structures under FreeBSD 5/6
>>>between the device functions and the kernel thread.
>>>
>>>How should I best do this under FreeBSD 4?
>>>
>>>Would something like splhigh() work in that context?
>>>Or should I use lockmgr with LK_EXCLUSIVE/LK_RELEASE?
>>>Is there any (pseudo)process context inside a kernel task?
>>
>>spltty() is what you probably need to use. you could just adjust the
>>following defines like
>>
>>#define VKBD_LOCK_DECL int
>>#define VKBD_LOCK_INIT(s) /* noop */
>>#define VKBD_LOCK_DESTROY(s) /* noop */
>>#define VKBD_LOCK(s) (s)->ks_lock = spltty()
>>#define VKBD_UNLOCK(s) splx((s)->ks_lock)
>>#define VKBD_LOCK_ASSERT(s, w)
>>#define VKBD_SLEEP(s, f, d, t) \
>> tsleep(&(s)->f, PCATCH | (PZERO + 1), d, t)
>
> The code above will probably crash the kernel in many spectacular and
> unpredictable ways. You will need to save interrupt flags locally to each
> VKBD_LOCK caller or they will end up restoring each other's flags.

yes, you are correct. my bad :( thanks for catching this

max
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