• Hugh Dickins's avatar
    [PATCH] mm: init_mm without ptlock · 872fec16
    Hugh Dickins authored
    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: default avatarHugh Dickins <hugh@veritas.com>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>