Came upon a strange thing with ddi_get_lbolt and cv_timedwait.
Following a code fragment to show the issue:
mutex_enter(&ptr->mutex);
while (ptr->busy != 0) {
clock_t until;
(void) ddi_get_lbolt(); /* just call function, seems not to work at first
call */
until = ddi_get_lbolt() + drv_usectohz(tmo);
if (cv_timedwait(&ptr->cv, &ptr->mutex, until) == -1) {
mutex_exit(&ptr->mutex);
err = EAGAIN;
goto somewhere_else;
}
}
mutex_exit(&mstr_ptr->vv_mutex);
In theory the line "(void) ddi_get_lbolt();" should be completely unnecessary.
But in case I omit this line and ddi_get_lbolt() has never been called before
in the driver cv_timedwait() will not return when timeout is reached without
the condition being signaled. Inserting that (in theory useless) line makes
everything work fine.
Did I understand or do something wrong or is it really a bug?
I'm a little bit unsure if I have seen this on all platforms. Last time I was
getting
into this trap was on Solaris x86 / single cpu machine.
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