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    ANDROID: binder: change down_write to down_read · 720c2419
    Minchan Kim 提交于
    binder_update_page_range needs down_write of mmap_sem because
    vm_insert_page need to change vma->vm_flags to VM_MIXEDMAP unless
    it is set. However, when I profile binder working, it seems
    every binder buffers should be mapped in advance by binder_mmap.
    It means we could set VM_MIXEDMAP in binder_mmap time which is
    already hold a mmap_sem as down_write so binder_update_page_range
    doesn't need to hold a mmap_sem as down_write.
    Please use proper API down_read. It would help mmap_sem contention
    problem as well as fixing down_write abuse.
    
    Ganesh Mahendran tested app launching and binder throughput test
    and he said he couldn't find any problem and I did binder latency
    test per Greg KH request(Thanks Martijn to teach me how I can do)
    I cannot find any problem, too.
    
    Cc: Ganesh Mahendran <opensource.ganesh@gmail.com>
    Cc: Joe Perches <joe@perches.com>
    Cc: Arve Hjønnevåg <arve@android.com>
    Cc: Todd Kjos <tkjos@google.com>
    Reviewed-by: NMartijn Coenen <maco@android.com>
    Signed-off-by: NMinchan Kim <minchan@kernel.org>
    Reviewed-by: NJoel Fernandes (Google) <joel@joelfernandes.org>
    Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    720c2419
binder_alloc.c 27.2 KB