Messages in this thread | | | Date | Wed, 21 Apr 1999 19:40:09 -0400 | From | Johannes Erdfelt <> | Subject | Re: mutexs for synchronization between kernel threads? |
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On Thu, Apr 22, 1999, V Ganesh <ganesh@vxindia.veritas.com> wrote: > > Well, under 2.2.6 spin_lock and spin_unlock in the non SMP case are > > NOOPS (do { } while(0)). This is not what I want. > > no, this _is_ what you want. remember that on UP, a kernel thread cannot > thread can be pre-empted unless it voluntarily blocks. this itself > guarantees mutual exclusion for your threads A and B. that's why spinlocks > are no-ops in UP. > what this means is that A and B do not run in "parallel". however, > interrupts may occur "in parallel" or asynchronous with A and B, so you > need to protect against them. > that's why you use spinlock_irqsave and spinlock_irqrestore to protect your > structures in A and B rather than plain spinlocks. they work out to > save_flags(flags);cli() and restore_flags(flags) in UP which is exactly > what you want.
Aha! This makes much more sense. I removed all of the semaphore/mutex stuff and stuck with the spinlocks.
I still had problems, but only in some circumstances. I tracked it down to adding a an entry to a list_head twice thus creating a circular list. The thread was never giving up processor control and eventually I'd get all kinds of weird oops'.
Thanks very much for clarification. This significantly simplifies things.
JE
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