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  • Petr Mladek's avatar
    kthread: add kthread_create_worker*() · fbae2d44
    Petr Mladek authored
    Kthread workers are currently created using the classic kthread API,
    namely kthread_run().  kthread_worker_fn() is passed as the @threadfn
    parameter.
    
    This patch defines kthread_create_worker() and
    kthread_create_worker_on_cpu() functions that hide implementation details.
    
    They enforce using kthread_worker_fn() for the main thread.  But I doubt
    that there are any plans to create any alternative.  In fact, I think that
    we do not want any alternative main thread because it would be hard to
    support consistency with the rest of the kthread worker API.
    
    The naming and function of kthread_create_worker() is inspired by the
    workqueues API like the rest of the kthread worker API.
    
    The kthread_create_worker_on_cpu() variant is motivated by the original
    kthread_create_on_cpu().  Note that we need to bind per-CPU kthread
    workers already when they are created.  It makes the life easier.
    kthread_bind() could not be used later for an already running worker.
    
    This patch does _not_ convert existing kthread workers.  The kthread
    worker API need more improvements first, e.g.  a function to destroy the
    worker.
    
    IMPORTANT:
    
    kthread_create_worker_on_cpu() allows to use any format of the worker
    name, in compare with kthread_create_on_cpu().  The good thing is that it
    is more generic.  The bad thing is that most users will need to pass the
    cpu number in two parameters, e.g.  kthread_create_worker_on_cpu(cpu,
    "helper/%d", cpu).
    
    To be honest, the main motivation was to avoid the need for an empty
    va_list.  The only legal way was to create a helper function that would be
    called with an empty list.  Other attempts caused compilation warnings or
    even errors on different architectures.
    
    There were also other alternatives, for example, using #define or
    splitting __kthread_create_worker().  The used solution looked like the
    least ugly.
    
    Link: http://lkml.kernel.org/r/1470754545-17632-6-git-send-email-pmladek@suse.com
    
    
    Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
    Acked-by: default avatarTejun Heo <tj@kernel.org>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
    Cc: Josh Triplett <josh@joshtriplett.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Jiri Kosina <jkosina@suse.cz>
    Cc: Borislav Petkov <bp@suse.de>
    Cc: Michal Hocko <mhocko@suse.cz>
    Cc: Vlastimil Babka <vbabka@suse.cz>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    fbae2d44