• Lai Jiangshan's avatar
    smpboot: Add missing get_online_cpus() in smpboot_register_percpu_thread() · 4bee9686
    Lai Jiangshan authored
    The following race exists in the smpboot percpu threads management:
    
    CPU0	      	   	     CPU1
    cpu_up(2)
      get_online_cpus();
      smpboot_create_threads(2);
    			     smpboot_register_percpu_thread();
    			     for_each_online_cpu();
    			       __smpboot_create_thread();
      __cpu_up(2);
    
    This results in a missing per cpu thread for the newly onlined cpu2 and
    in a NULL pointer dereference on a consecutive offline of that cpu.
    
    Proctect smpboot_register_percpu_thread() with get_online_cpus() to
    prevent that.
    
    [ tglx: Massaged changelog and removed the change in
            smpboot_unregister_percpu_thread() because that's an
            optimization and therefor not stable material. ]
    Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Rusty Russell <rusty@rustcorp.com.au>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: stable@vger.kernel.org
    Link: http://lkml.kernel.org/r/1406777421-12830-1-git-send-email-laijs@cn.fujitsu.comSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    4bee9686
smpboot.c 6.98 KB