• Steven Rostedt's avatar
    generic-ipi: use per cpu data for single cpu ipi calls · d7240b98
    Steven Rostedt authored
    The smp_call_function can be passed a wait parameter telling it to
    wait for all the functions running on other CPUs to complete before
    returning, or to return without waiting. Unfortunately, this is
    currently just a suggestion and not manditory. That is, the
    smp_call_function can decide not to return and wait instead.
    
    The reason for this is because it uses kmalloc to allocate storage
    to send to the called CPU and that CPU will free it when it is done.
    But if we fail to allocate the storage, the stack is used instead.
    This means we must wait for the called CPU to finish before
    continuing.
    
    Unfortunatly, some callers do no abide by this hint and act as if
    the non-wait option is mandatory. The MTRR code for instance will
    deadlock if the smp_call_function is set to wait. This is because
    the smp_call_function will wait for the other CPUs to finish their
    called functions, but those functions are waiting on the caller to
    continue.
    
    This patch changes the generic smp_call_function code to use per cpu
    variables if the allocation of the data fails for a single CPU call. The
    smp_call_function_many will fall back to the smp_call_function_single
    if it fails its alloc. The smp_call_function_single is modified
    to not force the wait state.
    
    Since we now are using a single data per cpu we must synchronize the
    callers to prevent a second caller modifying the data before the
    first called IPI functions complete. To do so, I added a flag to
    the call_single_data called CSD_FLAG_LOCK. When the single CPU is
    called (which can be called when a many call fails an alloc), we
    set the LOCK bit on this per cpu data. When the caller finishes
    it clears the LOCK bit.
    
    The caller must wait till the LOCK bit is cleared before setting
    it. When it is cleared, there is no IPI function using it.
    Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
    Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Acked-by: default avatarJens Axboe <jens.axboe@oracle.com>
    Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    d7240b98
smp.c 11.2 KB