• Paul E. McKenney's avatar
    rcu: Delay rcu_barrier() wait until beginning of next CPU-hotunplug operation. · 1423cc03
    Paul E. McKenney authored
    Ingo Molnar reported this lockup:
    
     [  200.380003] Hangcheck: hangcheck value past margin!
     [  248.192003] INFO: task S99local:2974 blocked for more than 120 seconds.
     [  248.194532] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
     [  248.202330] S99local      D 0000000c  6256  2974   2687 0x00000000
     [  248.208929]  9c7ebe90 00000086 6b67ef8b 0000000c 9f25a610 81a69869 00000001 820b6990
     [  248.216123]  820b6990 820b6990 9c6e4c20 9c6e4eb4 82c78990 00000000 6b993559 0000000c
     [  248.220616]  9c7ebe90 8105f22a 9c6e4eb4 9c6e4c20 00000001 9c7ebe98 9c7ebeb4 81a65cb3
     [  248.229990] Call Trace:
     [  248.234049]  [<81a69869>] ? _spin_unlock_irqrestore+0x22/0x37
     [  248.239769]  [<8105f22a>] ? prepare_to_wait+0x48/0x4e
     [  248.244796]  [<81a65cb3>] rcu_barrier_cpu_hotplug+0xaa/0xc9
     [  248.250343]  [<8105f029>] ? autoremove_wake_function+0x0/0x38
     [  248.256063]  [<81062cf2>] notifier_call_chain+0x49/0x71
     [  248.261263]  [<81062da0>] raw_notifier_call_chain+0x11/0x13
     [  248.266809]  [<81a0b475>] _cpu_down+0x272/0x288
     [  248.271316]  [<81a0b4d5>] cpu_down+0x4a/0xa2
     [  248.275563]  [<81a0c48a>] store_online+0x2a/0x5e
     [  248.280156]  [<81a0c460>] ? store_online+0x0/0x5e
     [  248.284836]  [<814ddc35>] sysdev_store+0x20/0x28
     [  248.289429]  [<8112e403>] sysfs_write_file+0xb8/0xe3
     [  248.294369]  [<8112e34b>] ? sysfs_write_file+0x0/0xe3
     [  248.299396]  [<810e4c8f>] vfs_write+0x91/0x120
     [  248.303817]  [<810e4dc1>] sys_write+0x40/0x65
     [  248.308150]  [<81002d73>] sysenter_do_call+0x12/0x28
    
    This change moves an RCU grace period delay off of the
    critical path for CPU-hotunplug operations.
    
    Since RCU callback migration is only performed on
    CPU-hotunplug operations, and since the rcu_barrier() race is
    provoked only by consecutive CPU-hotunplug operations, it is
    not necessary to delay the end of a given CPU-hotunplug
    operation.
    
    We can instead choose to delay the beginning of the next
    CPU-hotunplug operation.
    Reported-by: default avatarIngo Molnar <mingo@elte.hu>
    Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Josh Triplett <josht@linux.vnet.ibm.com>
    Cc: laijs@cn.fujitsu.com
    Cc: dipankar@in.ibm.com
    Cc: akpm@linux-foundation.org
    Cc: mathieu.desnoyers@polymtl.ca
    Cc: dvhltc@us.ibm.com
    Cc: niv@us.ibm.com
    Cc: peterz@infradead.org
    Cc: rostedt@goodmis.org
    Cc: hugh.dickins@tiscali.co.uk
    Cc: benh@kernel.crashing.org
    LKML-Reference: <20090819060614.GA14383@linux.vnet.ibm.com>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    1423cc03
rcupdate.c 7.77 KB