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SubjectRe: [PATCH 2/2] staging: lustre: disable preempt while sampling processor id.
Date
On Dec 18, 2017, at 16:01, NeilBrown <neilb@suse.com> wrote:
>
> Calling smp_processor_id() without disabling preemption
> triggers a warning (if CONFIG_DEBUG_PREEMPT).
> I think the result of cfs_cpt_current() is only used as a hint for
> load balancing, rather than as a precise and stable indicator of
> the current CPU. So it doesn't need to be called with
> preemption disabled.
>
> So disable preemption inside cfs_cpt_current() to silence the warning.
>
> Signed-off-by: NeilBrown <neilb@suse.com>

Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>

> ---
> .../staging/lustre/lnet/libcfs/linux/linux-cpu.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/staging/lustre/lnet/libcfs/linux/linux-cpu.c b/drivers/staging/lustre/lnet/libcfs/linux/linux-cpu.c
> index d30650f8dcb4..ca8518b8a3e0 100644
> --- a/drivers/staging/lustre/lnet/libcfs/linux/linux-cpu.c
> +++ b/drivers/staging/lustre/lnet/libcfs/linux/linux-cpu.c
> @@ -517,19 +517,20 @@ EXPORT_SYMBOL(cfs_cpt_spread_node);
> int
> cfs_cpt_current(struct cfs_cpt_table *cptab, int remap)
> {
> - int cpu = smp_processor_id();
> - int cpt = cptab->ctb_cpu2cpt[cpu];
> + int cpu;
> + int cpt;
>
> - if (cpt < 0) {
> - if (!remap)
> - return cpt;
> + preempt_disable();
> + cpu = smp_processor_id();
> + cpt = cptab->ctb_cpu2cpt[cpu];
>
> + if (cpt < 0 && remap) {
> /* don't return negative value for safety of upper layer,
> * instead we shadow the unknown cpu to a valid partition ID
> */
> cpt = cpu % cptab->ctb_nparts;
> }
> -
> + preempt_enable();
> return cpt;
> }
> EXPORT_SYMBOL(cfs_cpt_current);
>
>

Cheers, Andreas
--
Andreas Dilger
Lustre Principal Architect
Intel Corporation







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