Messages in this thread | | | Date | Thu, 10 Apr 2008 16:01:53 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [patch 11/17] Implement immediate update via stop_machine_run |
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* KOSAKI Motohiro (kosaki.motohiro@jp.fujitsu.com) wrote: > Hi > > > -Updating immediate values, cannot rely on smp_call_function() b/c synchronizing > > cpus using IPIs leads to deadlocks. Process A held a read lock on > > tasklist_lock, then process B called apply_imv_update(). Process A received the > > IPI and begins executing ipi_busy_loop(). Then process C takes a write lock > > irq on the task list lock, before receiving the IPI. Thus, process A holds up > > process C, and C can't get an IPI b/c interrupts are disabled. Solve this > > problem by using a new 'ALL_CPUS' parameter to stop_machine_run(). Which > > runs a function on all cpus after they are busy looping and have disabled > > irqs. Since this is done in a new process context, we don't have to worry > > about interrupted spin_locks. Also, less lines of code. Has survived 24 hours+ > > of testing... > > it seems this patch is must, Why do you separate patch [10/17] and [11/17]? > this patch remove almost portion of [10/17]. > IMHO these patch merge into 1 patch is better. >
Hi Kosaki,
You are right, I will merge them and resend them in the following post.
> > > +static int stop_machine_imv_update(void *imv_ptr) > > +{ > > + struct __imv *imv = imv_ptr; > > + > > + if (!wrote_text) { > > it seems racy. > Why don't need test_and_set? > > I think your stop_machine_run(ALL_CPUS) call fn concurrency... > The answer to this mistery is in include/linux/stop_machine.h modified by add-all-cpus-option-to-stop-machine-run.patch :
/** * stop_machine_run: freeze the machine on all CPUs and run this function * @fn: the function to run * @data: the data ptr for the @fn() - * @cpu: the cpu to run @fn() on (or any, if @cpu == NR_CPUS. + * @cpu: if @cpu == n, run @fn() on cpu n + * if @cpu == NR_CPUS, run @fn() on any cpu + * if @cpu == ALL_CPUS, run @fn() first on the calling cpu, and then + * concurrently on all the other cpus * * Description: This causes a thread to be scheduled on every other cpu, * each of which disables interrupts, and finally interrupts are disabled
Therefore, the first execution of the function is done before all other executions.
Thanks,
Mathieu
> > > + text_poke((void *)imv->imv, (void *)imv->var, imv->size); > > + wrote_text = 1; > > + smp_wmb(); /* make sure other cpus see that this has run */ > > + } else > > + sync_core(); > > + > > + flush_icache_range(imv->imv, imv->imv + imv->size); > > + > > + return 0; > > +} > > + > >
-- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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