Hi,
On 4/23/07, Eddie C. Dost <[email protected]> wrote:
as long as mutexes are not converted to nop when CONFIG_SMP is not
defined (I don't know what current kernels do), this is of course
correct. You need to verify the headerfiles for the above.
Yes, even on UP different threads accessing the same data could race.
Mutexes (== binary semaphores) are *required* to synchronize access to
shared data.
You might be confusing mutexes with spinlocks. Spinlocks _are_
compiled away on UP (actually !CONFIG_SMP && !CONFIG_PREEMPT) kernels,
but that is still safe because spinlocks are busy-waiting loops
(unlike mutexes and semaphores that block) and hence no thread is
allowed to sleep when holding a spinlock.
On Mon, Apr 23, 2007 at 09:40:26AM +0200, Matthias Kaehlcke wrote:
> El Mon, Apr 23, 2007 at 09:16:08AM +0200 Eddie C. Dost ha dit:
> > Please note that the semaphore is used to lock the idt77252 config
> > tables among multiple users including atmsigd even on single processor
> > machines. Does this work with mutexes?
>
> afaik mutexes have the same behaviour as binary semaphores that are
> used as mutexes (always locked and unlocked by the same
> process/thread):
Mutexes / binary semaphores / spinlocks are used to synchronize access
to shared data by *multiple* threads ... there is no meaning in
locking access to something if we know only one thread will ever touch
it.
Cheers,
S
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