Messages in this thread | | | Date | Tue, 2 Oct 2012 13:25:24 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH v3 -tip 1/5] x86, MSI: Support multiple MSIs in presense of IRQ remapping |
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* Alexander Gordeev <agordeev@redhat.com> wrote:
> On Tue, Oct 02, 2012 at 06:55:18AM +0200, Ingo Molnar wrote: > > Thanks for the review, Ingo. > > > > @@ -584,8 +586,12 @@ int __irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node, > > > #define irq_alloc_desc_from(from, node) \ > > > irq_alloc_descs(-1, from, 1, node) > > > > > > +#define irq_alloc_descs_from(from, cnt, node) \ > > > + irq_alloc_descs(-1, from, cnt, node) > > > + > > > > Please use inlines instead of macros. Might transform the one > > above it as well in the process. > > You mean here do not introduce irq_alloc_descs_from, but rather use > irq_alloc_descs() directly?
My suggestion is to add irq_alloc_descs_from() as a (very simple) inline function and change irq_alloc_desc_from() to be an inline function as well.
> > > +int irq_can_alloc_irqs(unsigned int from, unsigned int cnt) > > > +{ > > > + unsigned int start; > > > + int ret = 0; > > > + > > > + if (!cnt) > > > + return -EINVAL; > > > + > > > + mutex_lock(&sparse_irq_lock); > > > + start = bitmap_find_next_zero_area(allocated_irqs, IRQ_BITMAP_BITS, > > > + from, cnt, 0); > > > + mutex_unlock(&sparse_irq_lock); > > > + if (start + cnt > nr_irqs) > > > + ret = irq_can_expand_nr_irqs(start + cnt); > > > + return ret; > > > > How is this supposed to work wrt. races? > > It is not supposed. Just a quick check if there are enough bits before an > attempt to allocate memory in __create_irqs(). Otherwise __create_irqs() > might allocate irq_cfg's, then realize there are no bits, then deallocate > and fail. > > But strictly speaking, irq_can_alloc_irqs() is unnecessary.
Why complicate it if it's unnecessary? The function is inviting wrong logic: it *cannot* tell whether there are enough bits, because the check is racy.
So I'd suggest to keep this out - this will further simplify the patches.
Thanks,
Ingo
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