Messages in this thread |  | | Date | Wed, 2 Jan 2013 15:12:42 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH v4] lib: cpu_rmap: avoid flushing all workqueues |
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On Wed, 2 Jan 2013 13:52:25 -0800 David Decotigny <decot@googlers.com> wrote:
> In some cases, free_irq_cpu_rmap() is called while holding a lock > (eg. rtnl). This can lead to deadlocks, because it invokes > flush_scheduled_work() which ends up waiting for whole system > workqueue to flush, but some pending works might try to acquire the > lock we are already holding. > > This commit uses reference-counting to replace > irq_run_affinity_notifiers(). It also removes > irq_run_affinity_notifiers() altogether.
I can't say that I've ever noticed cpu_rmap.c before :( Is is too late to review it?
- The naming is chaotic. At least these:
EXPORT_SYMBOL(alloc_cpu_rmap); EXPORT_SYMBOL(free_cpu_rmap); EXPORT_SYMBOL(cpu_rmap_add); EXPORT_SYMBOL(cpu_rmap_update); EXPORT_SYMBOL(free_irq_cpu_rmap); EXPORT_SYMBOL(irq_cpu_rmap_add);
should be consistently named cpu_rmap_foo()
- What's the locking model? It appears to be caller-provided, but it is undocumented.
drivers/net/ethernet/mellanox/mlx4/ appears to be using msix_ctl.pool_lock for exclusion, but I didn't check for coverage.
drivers/net/ethernet/sfc/efx.c seems to not need locking because all its cpu_rmap operations are at module_init() time.
The cpu_rmap code would be less of a hand grenade if each of its interface functions documented the caller's locking requirements.
As for this patch: there's no cc:stable here but it does appear that the problem is sufficiently serious to justify a backport, agree?
> --- a/include/linux/cpu_rmap.h > +++ b/include/linux/cpu_rmap.h > > ... > > @@ -33,15 +36,7 @@ struct cpu_rmap { > #define CPU_RMAP_DIST_INF 0xffff > > extern struct cpu_rmap *alloc_cpu_rmap(unsigned int size, gfp_t flags); > - > -/** > - * free_cpu_rmap - free CPU affinity reverse-map > - * @rmap: Reverse-map allocated with alloc_cpu_rmap(), or %NULL > - */ > -static inline void free_cpu_rmap(struct cpu_rmap *rmap) > -{ > - kfree(rmap); > -} > +extern void free_cpu_rmap(struct cpu_rmap *rmap);
Can we do away with free_cpu_rmap() altogether? It is a misleading name - it is a put() function, not a free() function. It would be clearer (not to mention faster and smaller) to change all call sites to directly call cpu_rmap_put().
> extern int cpu_rmap_add(struct cpu_rmap *rmap, void *obj); > extern int cpu_rmap_update(struct cpu_rmap *rmap, u16 index, > > ... > > @@ -63,6 +64,44 @@ struct cpu_rmap *alloc_cpu_rmap(unsigned int size, gfp_t flags) > } > EXPORT_SYMBOL(alloc_cpu_rmap); > > +/** > + * cpu_rmap_reclaim - internal reclaiming helper called from kref_put > + * @ref: kref to struct cpu_rmap > + */ > +static void cpu_rmap_reclaim(struct kref *ref) > +{ > + struct cpu_rmap *rmap = container_of(ref, struct cpu_rmap, refcount); > + kfree(rmap); > +}
I suggest this be renamed to cpu_rmap_release(). As "release" is the conventional term for a kref release handler.
> > ... > > +/** > + * cpu_rmap_put - internal helper to release ref on a cpu_rmap > + * @rmap: reverse-map allocated with alloc_cpu_rmap() > + */ > +static inline void cpu_rmap_put(struct cpu_rmap *rmap) > +{ > + kref_put(&rmap->refcount, cpu_rmap_reclaim); > +}
As mentioned, I suggest this become the public interface. And I suppose it should propagate kref_put()'s return value, in case someone is interested.
> +/** > + * free_cpu_rmap - free CPU affinity reverse-map > + * @rmap: Reverse-map allocated with alloc_cpu_rmap() > + */ > +void free_cpu_rmap(struct cpu_rmap *rmap) > +{ > + cpu_rmap_put(rmap); > +} > +EXPORT_SYMBOL(free_cpu_rmap);
zap.
> /* Reevaluate nearest object for given CPU, comparing with the given > * neighbours at the given distance. > */ > > ... >
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