• Hugh Dickins's avatar
    [PATCH] mm: ptd_alloc take ptlock · c74df32c
    Hugh Dickins authored
    Second step in pushing down the page_table_lock.  Remove the temporary
    bridging hack from __pud_alloc, __pmd_alloc, __pte_alloc: expect callers not
    to hold page_table_lock, whether it's on init_mm or a user mm; take
    page_table_lock internally to check if a racing task already allocated.
    Convert their callers from common code.  But avoid coming back to change them
    again later: instead of moving the spin_lock(&mm->page_table_lock) down,
    switch over to new macros pte_alloc_map_lock and pte_unmap_unlock, which
    encapsulate the mapping+locking and unlocking+unmapping together, and in the
    end may use alternatives to the mm page_table_lock itself.
    These callers all hold mmap_sem (some exclusively, some not), so at no level
    can a page table be whipped away from beneath them; and pte_alloc uses the
    "atomic" pmd_present to test whether it needs to allocate.  It appears that on
    all arches we can safely descend without page_table_lock.
    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>
fork.c 32.4 KB