On Sun, 2003-03-09 at 18:44, Zwane Mwaikambo wrote:
> --- linux-2.5.64-unwashed/include/linux/brlock.h 5 Mar 2003 05:07:54 -0000 1.1.1.1
> +++ linux-2.5.64-unwashed/include/linux/brlock.h 9 Mar 2003 23:42:26 -0000
> @@ -85,8 +85,7 @@
> if (idx >= __BR_END)
> __br_lock_usage_bug();
>
> - preempt_disable();
> - _raw_read_lock(&__brlock_array[smp_processor_id()][idx]);
> + read_lock(&__brlock_array[smp_processor_id()][idx]);
> }
This is wrong.
We have to disable preemption prior to reading smp_processor_id().
Otherwise we may lock/unlock the wrong processor's brlock. The above as
you changed it is equivalent to:
cpu = smp_processor_id();
/* do not want to preempt here, but we can! */
preempt_disable();
_raw_read_lock(&__brlock_array[cpu][idx]);
And what we had, and what we need, is:
preempt_disable();
cpu = smp_processor_id();
_raw_read_lock(&__brlock_array[cpu][idx]);
In other words, we need to ensure preemption is disabled prior to
calling smp_processor_id().
We also do something similar with the write patch in lib/brlock.c, but
for different reason: to disable preemption once and not NR_CPUS times.
The rest of the patch looks fine. :)
Robert Love
-
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This archive was generated by hypermail 2b29 : Sat Mar 15 2003 - 22:00:20 EST