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options RND_COM considered dangeous
I just got a locking-against-myself panic on an XScale pxa250 (ARM)
system running a -current from shortly before the creation of the
netbsd-5 branch while doing a build of some stuff from pkgsrc. The
trace (partially copied by hand because I over-wrote the log :() is
panic: lock error
Stopped in pid 12381.1 (ftp) at netbsd:cpu_Debugger+0x4: bx r14
(The lock error in this case was a locking-against-myself panic; this is
a LOCKDEBUG/DIAGNOSTIC kernel).
It looks like the problem is that the callout data is protected by locks
at IPL_SCHED whereas com(4) interrupts at IPL_HIGH; the lock that is being
locked recursively is the callout lock.
I don't know if there are serial drivers that run at-or-below-IPL_SCHED,
but if not, it might make sense to remove the RND_COM option.
Time is an illusion; lunchtime, doubly so. |/\/\| Rafal Boni
-- Ford Prefect |\/\/|
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