• Hugh Dickins's avatar
    [SPARC64] mm: context switch ptlock · dedeb002
    Hugh Dickins authored
    sparc64 is unique among architectures in taking the page_table_lock in
    its context switch (well, cris does too, but erroneously, and it's not
    yet SMP anyway).
    This seems to be a private affair between switch_mm and activate_mm,
    using page_table_lock as a per-mm lock, without any relation to its uses
    elsewhere.  That's fine, but comment it as such; and unlock sooner in
    switch_mm, more like in activate_mm (preemption is disabled here).
    There is a block of "if (0)"ed code in smp_flush_tlb_pending which would
    have liked to rely on the page_table_lock, in switch_mm and elsewhere;
    but its comment explains how dup_mmap's flush_tlb_mm defeated it.  And
    though that could have been changed at any time over the past few years,
    now the chance vanishes as we push the page_table_lock downwards, and
    perhaps split it per page table page.  Just delete that block of code.
    Which leaves the mysterious spin_unlock_wait(&oldmm->page_table_lock)
    in kernel/fork.c copy_mm.  Textual analysis (supported by Nick Piggin)
    suggests that the comment was written by DaveM, and that it relates to
    the defeated approach in the sparc64 smp_flush_tlb_pending.  Just delete
    this block too.
    Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
fork.c 32.2 KB