• Frederic Weisbecker's avatar
    smp: Remove wait argument from __smp_call_function_single() · fce8ad15
    Frederic Weisbecker authored
    The main point of calling __smp_call_function_single() is to send
    an IPI in a pure asynchronous way. By embedding a csd in an object,
    a caller can send the IPI without waiting for a previous one to complete
    as is required by smp_call_function_single() for example. As such,
    sending this kind of IPI can be safe even when irqs are disabled.
    This flexibility comes at the expense of the caller who then needs to
    synchronize the csd lifecycle by himself and make sure that IPIs on a
    single csd are serialized.
    This is how __smp_call_function_single() works when wait = 0 and this
    usecase is relevant.
    Now there don't seem to be any usecase with wait = 1 that can't be
    covered by smp_call_function_single() instead, which is safer. Lets look
    at the two possible scenario:
    1) The user calls __smp_call_function_single(wait = 1) on a csd embedded
       in an object. It looks like a nice and convenient pattern at the first
       sight because we can then retrieve the object from the IPI handler easily.
       But actually it is a waste of memory space in the object since the csd
       can be allocated from the stack by smp_call_function_single(wait = 1)
       and the object can be passed an the IPI argument.
       Besides that, embedding the csd in an object is more error prone
       because the caller must take care of the serialization of the IPIs
       for this csd.
    2) The user calls __smp_call_function_single(wait = 1) on a csd that
       is allocated on the stack. It's ok but smp_call_function_single()
       can do it as well and it already takes care of the allocation on the
       stack. Again it's more simple and less error prone.
    Therefore, using the underscore prepend API version with wait = 1
    is a bad pattern and a sign that the caller can do safer and more
    There was a single user of that which has just been converted.
    So lets remove this option to discourage further users.
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Christoph Hellwig <hch@infradead.org>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Jan Kara <jack@suse.cz>
    Cc: Jens Axboe <axboe@fb.com>
    Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
    Signed-off-by: default avatarJens Axboe <axboe@fb.com>
up.c 1.72 KB