• Petr Mladek's avatar
    kthread: detect when a kthread work is used by more workers · 8197b3d4
    Petr Mladek authored
    Nothing currently prevents a work from queuing for a kthread worker when
    it is already running on another one.  This means that the work might run
    in parallel on more than one worker.  Also some operations are not
    reliable, e.g.  flush.
    
    This problem will be even more visible after we add kthread_cancel_work()
    function.  It will only have "work" as the parameter and will use
    worker->lock to synchronize with others.
    
    Well, normally this is not a problem because the API users are sane.
    But bugs might happen and users also might be crazy.
    
    This patch adds a warning when we try to insert the work for another
    worker.  It does not fully prevent the misuse because it would make the
    code much more complicated without a big benefit.
    
    It adds the same warning also into kthread_flush_work() instead of the
    repeated attempts to get the right lock.
    
    A side effect is that one needs to explicitly reinitialize the work if it
    must be queued into another worker.  This is needed, for example, when the
    worker is stopped and started again.  It is a bit inconvenient.  But it
    looks like a good compromise between the stability and complexity.
    
    I have double checked all existing users of the kthread worker API and
    they all seems to initialize the work after the worker gets started.
    
    Just for completeness, the patch adds a check that the work is not already
    in a queue.
    
    The patch also puts all the checks into a separate function.  It will be
    reused when implementing delayed works.
    
    Link: http://lkml.kernel.org/r/1470754545-17632-8-git-send-email-pmladek@suse.comSigned-off-by: default avatarPetr Mladek <pmladek@suse.com>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Tejun Heo <tj@kernel.org>
    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>
    8197b3d4
kthread.c 23.2 KB