Messages in this thread | | | Date | Thu, 7 Jun 2007 22:48:10 +0530 | From | "Satyam Sharma" <> | Subject | Re: [patch] i386/x86_64: smp_call_function locking inconsistency |
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> On 6/7/07, Heiko Carstens <heiko.carstens@de.ibm.com> wrote: > [...] > > Avi Kivity has already a patch which introduces an on_cpu() function which > > looks quite like on_each_cpu(). That way you don't have to open code this > > stuff over and over again: > > > > preempt_disable(); > > if (cpu == smp_processor_id()) > > func(); > > else > > smp_call_function_single(...); > > preempt_enable(); > > > > There are already quite a few of these around. > > Indeed -- this was doubly problematic because the un-safeness > was because of smp_processor_id() as well as the (eventual) > access of cpu_online_map (via smp_call_function() -> > num_online_cpus()) ... thanks for letting me know about this.
Oh wait, the on_one_cpu() patch proposes on UP:
+static inline int on_one_cpu(int cpu, void (*func)(void *info), void *info, + int retry, int wait) +{
/* this needs a if (cpu == 0) check here, IMO */
+ local_irq_disable(); + func(info); + local_irq_enable(); + return 0;
/* else WARN and return -EINVAL; */
+}
which is broken without the suggested additions, IMHO (this is what got me into this in the first place). There _is_ a difference between on_each_cpu() and the smp_call_function* semantics (as discussed on the other thread -- gargh! my mistake for opening this discussion up on so many threads), and in its current form on_one_cpu() has quite confused semantics, trying to mix the two. I guess on_one_cpu() would be better off simply being just an atomic wrapper over smp_processor_id() and smp_call_function_single() (which is the *real* issue that needs solving in the first place), and do it well.
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