Subject: Re: kprintf locking problem.
To: Anders Magnusson <email@example.com>
From: Jason R Thorpe <firstname.lastname@example.org>
Date: 06/03/2001 08:07:36
On Sun, Jun 03, 2001 at 04:55:04PM +0200, Anders Magnusson wrote:
> The kernel printf routines are protected by a spinlock so that only
> one processor can be in the printf routnes at the same time. I assume
> that this locking is to protect the console hardware from being accessed
> from more than one CPU at a time. This causes problem on machines where
> only one CPU can access the system console and the rest must send their
> data over via IPI: if a slave CPU enters the printf routines, and then
> the master CPU also tries to do a printf, the master will spinlock at
> high ipl. Meanwhile the slave has reached putchar() and sends an IPI
> which will never reach the master, hence the deadlock.
Well, it's also designed to prevent interleaved printf characters, i.e.
you want to be able to see:
Does the VAX's scheme deal with that okay? Also, where do you want
to put the new #define? Probably should be in sys/types.h, or something,
-- Jason R. Thorpe <email@example.com>