On Wed, Feb 21, 2007 at 12:50:44PM -0500, Andrew Gallatin wrote:
...
> Speaking of icky, I'm really worried about the pedantic nature of
> FreeBSD's WITNESS and "never, ever sleep while holding a mutex" dogma
> causing as many problems as it solves. For example, iwi seems to
> simply drop its lock when loading firmware (presumably to avoid
> WITNESS squawking about holding a mutex while grabbing an sx). This
> certainly shuts up WITNESS, but it may also introduce a race,
> especially if the linker needs to sleep and wait for the disk.
i am not sure i follow you here...
Of course when you drop the lock you risk that the underlying
data structure is manipulated (or in the worst case freed),
but usually you can avoid this with something like
<while locked>
sc->flags |= LEAVE_ME_ALONE
UNLOCK
do_something_blocking()
LOCK
sc->flags &= ~LEAVE_ME_ALONE
do_something_else()
if (sc->flags & I_AM_WAITING) {
sc->flags &= ~I_AM_WAITING;
wakeup(sc);
}
UNLOCK
while others would do
LOCK(sc->mtx)
while (sc->flags & LEAVE_ME_ALONE) {
sc->flags |= I_AM_WAITING;
msleep(sc, &sc->mtx, ...)
}
to synchronize...
cheers
luigi