mutual exclusion in vkbd
Alexander Kabaev
kan at freebsd.org
Tue May 31 13:19:09 PDT 2005
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.
--
Alexander Kabaev
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