From 872fec16d9a0ed3b75b8893aa217e49cca575ee5 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Sat, 29 Oct 2005 18:16:21 -0700 Subject: [PATCH] mm: init_mm without ptlock First step in pushing down the page_table_lock. init_mm.page_table_lock has been used throughout the architectures (usually for ioremap): not to serialize kernel address space allocation (that's usually vmlist_lock), but because pud_alloc,pmd_alloc,pte_alloc_kernel expect caller holds it. Reverse that: don't lock or unlock init_mm.page_table_lock in any of the architectures; instead rely on pud_alloc,pmd_alloc,pte_alloc_kernel to take and drop it when allocating a new one, to check lest a racing task already did. Similarly no page_table_lock in vmalloc's map_vm_area. Some temporary ugliness in __pud_alloc and __pmd_alloc: since they also handle user mms, which are converted only by a later patch, for now they have to lock differently according to whether or not it's init_mm. If sources get muddled, there's a danger that an arch source taking init_mm.page_table_lock will be mixed with common source also taking it (or neither take it). So break the rules and make another change, which should break the build for such a mismatch: remove the redundant mm arg from pte_alloc_kernel (ppc64 scrapped its distinct ioremap_mm in 2.6.13). Exceptions: arm26 used pte_alloc_kernel on user mm, now pte_alloc_map; ia64 used pte_alloc_map on init_mm, now pte_alloc_kernel; parisc had bad args to pmd_alloc and pte_alloc_kernel in unused USE_HPPA_IOREMAP code; ppc64 map_io_page forgot to unlock on failure; ppc mmu_mapin_ram and ppc64 im_free took page_table_lock for no good reason. Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memory.c | 60 +++++++++++++++++++++++++++--------------------------------- 1 file changed, 27 insertions(+), 33 deletions(-) (limited to 'mm/memory.c') diff --git a/mm/memory.c b/mm/memory.c index 692ad810263..95a4553c75f 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -307,28 +307,22 @@ out: return pte_offset_map(pmd, address); } -pte_t fastcall * pte_alloc_kernel(struct mm_struct *mm, pmd_t *pmd, unsigned long address) +pte_t fastcall * pte_alloc_kernel(pmd_t *pmd, unsigned long address) { if (!pmd_present(*pmd)) { pte_t *new; - spin_unlock(&mm->page_table_lock); - new = pte_alloc_one_kernel(mm, address); - spin_lock(&mm->page_table_lock); + new = pte_alloc_one_kernel(&init_mm, address); if (!new) return NULL; - /* - * Because we dropped the lock, we should re-check the - * entry, as somebody else could have populated it.. - */ - if (pmd_present(*pmd)) { + spin_lock(&init_mm.page_table_lock); + if (pmd_present(*pmd)) pte_free_kernel(new); - goto out; - } - pmd_populate_kernel(mm, pmd, new); + else + pmd_populate_kernel(&init_mm, pmd, new); + spin_unlock(&init_mm.page_table_lock); } -out: return pte_offset_kernel(pmd, address); } @@ -2097,30 +2091,30 @@ int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma, #ifndef __PAGETABLE_PUD_FOLDED /* * Allocate page upper directory. - * - * We've already handled the fast-path in-line, and we own the - * page table lock. + * We've already handled the fast-path in-line. */ pud_t fastcall *__pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address) { pud_t *new; - spin_unlock(&mm->page_table_lock); + if (mm != &init_mm) /* Temporary bridging hack */ + spin_unlock(&mm->page_table_lock); new = pud_alloc_one(mm, address); - spin_lock(&mm->page_table_lock); - if (!new) + if (!new) { + if (mm != &init_mm) /* Temporary bridging hack */ + spin_lock(&mm->page_table_lock); return NULL; + } - /* - * Because we dropped the lock, we should re-check the - * entry, as somebody else could have populated it.. - */ + spin_lock(&mm->page_table_lock); if (pgd_present(*pgd)) { pud_free(new); goto out; } pgd_populate(mm, pgd, new); out: + if (mm == &init_mm) /* Temporary bridging hack */ + spin_unlock(&mm->page_table_lock); return pud_offset(pgd, address); } #endif /* __PAGETABLE_PUD_FOLDED */ @@ -2128,24 +2122,22 @@ pud_t fastcall *__pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long addr #ifndef __PAGETABLE_PMD_FOLDED /* * Allocate page middle directory. - * - * We've already handled the fast-path in-line, and we own the - * page table lock. + * We've already handled the fast-path in-line. */ pmd_t fastcall *__pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address) { pmd_t *new; - spin_unlock(&mm->page_table_lock); + if (mm != &init_mm) /* Temporary bridging hack */ + spin_unlock(&mm->page_table_lock); new = pmd_alloc_one(mm, address); - spin_lock(&mm->page_table_lock); - if (!new) + if (!new) { + if (mm != &init_mm) /* Temporary bridging hack */ + spin_lock(&mm->page_table_lock); return NULL; + } - /* - * Because we dropped the lock, we should re-check the - * entry, as somebody else could have populated it.. - */ + spin_lock(&mm->page_table_lock); #ifndef __ARCH_HAS_4LEVEL_HACK if (pud_present(*pud)) { pmd_free(new); @@ -2161,6 +2153,8 @@ pmd_t fastcall *__pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long addr #endif /* __ARCH_HAS_4LEVEL_HACK */ out: + if (mm == &init_mm) /* Temporary bridging hack */ + spin_unlock(&mm->page_table_lock); return pmd_offset(pud, address); } #endif /* __PAGETABLE_PMD_FOLDED */ -- cgit v1.2.3