arch/tile: fix up locking in pgtable.c slightly
We should be holding the init_mm.page_table_lock in shatter_huge_page() since we are modifying the kernel page tables. Then, only if we are walking the other root page tables to update them, do we want to take the pgd_lock. Add a comment about taking the pgd_lock that we always do it with interrupts disabled and therefore are not at risk from the tlbflush IPI deadlock as is seen on x86. Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
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@ -177,14 +177,10 @@ void shatter_huge_page(unsigned long addr)
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if (!pmd_huge_page(*pmd))
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return;
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/*
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* Grab the pgd_lock, since we may need it to walk the pgd_list,
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* and since we need some kind of lock here to avoid races.
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*/
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spin_lock_irqsave(&pgd_lock, flags);
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spin_lock_irqsave(&init_mm.page_table_lock, flags);
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if (!pmd_huge_page(*pmd)) {
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/* Lost the race to convert the huge page. */
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spin_unlock_irqrestore(&pgd_lock, flags);
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spin_unlock_irqrestore(&init_mm.page_table_lock, flags);
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return;
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}
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@ -194,6 +190,7 @@ void shatter_huge_page(unsigned long addr)
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#ifdef __PAGETABLE_PMD_FOLDED
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/* Walk every pgd on the system and update the pmd there. */
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spin_lock(&pgd_lock);
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list_for_each(pos, &pgd_list) {
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pmd_t *copy_pmd;
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pgd = list_to_pgd(pos) + pgd_index(addr);
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@ -201,6 +198,7 @@ void shatter_huge_page(unsigned long addr)
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copy_pmd = pmd_offset(pud, addr);
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__set_pmd(copy_pmd, *pmd);
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}
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spin_unlock(&pgd_lock);
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#endif
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/* Tell every cpu to notice the change. */
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@ -208,7 +206,7 @@ void shatter_huge_page(unsigned long addr)
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cpu_possible_mask, NULL, 0);
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/* Hold the lock until the TLB flush is finished to avoid races. */
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spin_unlock_irqrestore(&pgd_lock, flags);
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spin_unlock_irqrestore(&init_mm.page_table_lock, flags);
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}
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/*
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@ -217,9 +215,13 @@ void shatter_huge_page(unsigned long addr)
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* against pageattr.c; it is the unique case in which a valid change
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* of kernel pagetables can't be lazily synchronized by vmalloc faults.
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* vmalloc faults work because attached pagetables are never freed.
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* The locking scheme was chosen on the basis of manfred's
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* recommendations and having no core impact whatsoever.
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* -- wli
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*
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* The lock is always taken with interrupts disabled, unlike on x86
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* and other platforms, because we need to take the lock in
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* shatter_huge_page(), which may be called from an interrupt context.
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* We are not at risk from the tlbflush IPI deadlock that was seen on
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* x86, since we use the flush_remote() API to have the hypervisor do
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* the TLB flushes regardless of irq disabling.
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*/
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DEFINE_SPINLOCK(pgd_lock);
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LIST_HEAD(pgd_list);
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