Messages in this thread | | | Date | Fri, 11 Nov 2011 09:15:18 +0100 | From | Michal Hocko <> | Subject | Re: [PATCH 2/3] tile: remove irqsave pgd_lock locking |
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On Thu 10-11-11 13:50:05, Chris Metcalf wrote: > On 11/9/2011 10:47 AM, Michal Hocko wrote: > >a79e53d8: x86/mm: Fix pgd_lock deadlock dropped irqsave locking to fix a > >deadlock. pgd_lock is not used from an irq context so we can drop > >irqsave locking here as well. > >The original patch was x86 only but the same applies here > >because pgd_ctor (aka mm_alloc_pgd), pgd_dtor (aka mm_free_pgd), > >shatter_huge_page (not used anywhere) and vmalloc_sync_all are not used > >from an interrupt contexts. > > In fact, shatter_huge_page() is used by some code in our internal > version of arch/tile/mm/homecache.c that we haven't yet pushed back > to the community, and that CAN be called from an interrupt context. > (For example, we may shatter a huge page to dynamically change the > "home cache" of a small page when it's allocated from the page > allocator, causing us to need to map all the memory under the old > huge page with separate small pages that can now each carry separate > "home cache" locations for those pages.)
OK
> > We don't suffer from the x86 deadlock risk, since we handle TLB > flushing using our hypervisor API, flush_remote(), which doesn't pay > attention to the irq-disabled state on the remote core.
this deserves a comment in the code
> > So this patch would not be safe for our architecture, but thanks for > exploring the possibility. I'll add some comments explaining this > (at the definition of pgd_lock) to avoid confusion in the future.
great
> In fact, reviewing the shatter_huge_page() code, I realize I should > hold init_mm.page_table_lock as well as pgtable_lock to guard > against another thread updating init_mm in parallel; I think this is > only a theoretical issue but I'll add the locking to be consistent. > > -- > Chris Metcalf, Tilera Corp. > http://www.tilera.com
Thanks -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic
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