Messages in this thread |  | | | Date | Mon, 5 Mar 2012 20:53:54 +0000 | | From | Al Viro <> | | Subject | Re: [PATCH 3/3] flush_tlb_range() needs ->page_table_lock when ->mmap_sem is not held |
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On Mon, Mar 05, 2012 at 12:30:19PM -0800, Linus Torvalds wrote: > Is this safe? And why does it need it? Please add more explanations.
a) safety - as the matter of fact, all other callers either hold either ->mmap_sem (exclusive) or ->page_table_lock. flush_tlb_range() is called under ->page_table_lock in a lot of places, e.g. page_referenced_one() -> pmdp_clear_flush_young_notify() -> -> pmdp_clear_flush_young() -> flush_tlb_range(), with /* go ahead even if the pmd is pmd_trans_splitting() */ if (pmdp_clear_flush_young_notify(vma, address, pmd)) referenced++; spin_unlock(&mm->page_table_lock); in page_referenced_one(). b) there are instances that work with page tables. See e.g. arch/powerpc/mm/tlb_hash32.c, flush_tlb_range() and flush_range() in there. The same goes for uml, with a lot more extensive playing with page tables.
Almost all callers are actually fine - flush_tlb_range() may have no need to bother playing with page tables, but it can do so safely; again, this caller is the sole exception - everything else either has exclusive ->mmap_sem on the mm in question, or mm->page_table_lock is held.
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