John Baldwin wrote:
On Thursday 25 May 2006 23:01, Scott Long wrote:
Warner Losh wrote:
imp 2006-05-25 23:06:38 UTC
FreeBSD src repository
Modified files:
sys/dev/syscons/apm apm_saver.c
sys/i386/bios apm.c apm.h
Log:
APM was calling the suspend process from a timeout. This meant that
other timeouts could not happen while suspending, including timeouts
for things like msleep. This caused the system to hang on suspend
when the cbb was enabled, since its suspend path powered down the
socket which used a timeout to wait for it to be done.
APM now creates a thread when it is enabled, and deletes the thread
when it is disabled. This thread takes the place of the timeout by
doing its polling every ~.9s. When the thread is disabled, it will
wakeup early, otherwise it times out and polls the varius things the
old timeout polled (APM events, suspend delays, etc).
This makes my Sony VAIO 505TS suspend/resume correctly when APM is
enabled (ACPI is black listed on my 505TS).
This will likely fix other problems with the suspend path where
drivers would sleep with msleep and/or do other timeouts. Maybe
there's some special case code that would use DELAY while suspending
and msleep otherwise that can be revisited and removed.
This was also tested by glebius@, who pointed out that in the patch I
sent him, I'd forgotten apm_saver.c
MFC After: 3 weeks
In the past, I've been against mandating that callouts/timeouts/generic
taskqueues should not be allowed to sleep. However, after looking over
the history of this problem as well as others, it seems that it's just
too easy for driver authors to make bad assumptions and wind up with a
priority inversion/deadlock like this. It would be relatively trivial
to mark these contexts as being non-sleepable and have the msleep code
enforce it, like is done with ithreads. What do you think? Anyways,
thanks for looking at this and fixing it.
We already do for timeouts if INVARIANTS is on:
softclock()
{
...
THREAD_NO_SLEEPING();
c_func(c_arg);
THREAD_SLEEPING_OK();
...
}
That has been in place since 6.0 IIRC.
I thought that it was only enabled for DIAGNOSTIC.
Scott
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