• Greg Thelen's avatar
    ioprio: grab rcu_read_lock in sys_ioprio_{set,get}() · d69b78ba
    Greg Thelen authored
    Using:
    - CONFIG_LOCKUP_DETECTOR=y
    - CONFIG_PREEMPT=y
    - CONFIG_LOCKDEP=y
    - CONFIG_PROVE_LOCKING=y
    - CONFIG_PROVE_RCU=y
    found a missing rcu lock during boot on a 512 MiB x86_64 ubuntu vm:
      ===================================================
      [ INFO: suspicious rcu_dereference_check() usage. ]
      ---------------------------------------------------
      kernel/pid.c:419 invoked rcu_dereference_check() without protection!
    
      other info that might help us debug this:
    
      rcu_scheduler_active = 1, debug_locks = 0
      1 lock held by ureadahead/1355:
       #0:  (tasklist_lock){.+.+..}, at: [<ffffffff8115bc09>] sys_ioprio_set+0x7f/0x29e
    
      stack backtrace:
      Pid: 1355, comm: ureadahead Not tainted 2.6.37-dbg-DEV #1
      Call Trace:
       [<ffffffff8109c10c>] lockdep_rcu_dereference+0xaa/0xb3
       [<ffffffff81088cbf>] find_task_by_pid_ns+0x44/0x5d
       [<ffffffff81088cfa>] find_task_by_vpid+0x22/0x24
       [<ffffffff8115bc3e>] sys_ioprio_set+0xb4/0x29e
       [<ffffffff8147cf21>] ? trace_hardirqs_off_thunk+0x3a/0x3c
       [<ffffffff8105c409>] sysenter_dispatch+0x7/0x2c
       [<ffffffff8147cee2>] ? trace_hardirqs_on_thunk+0x3a/0x3f
    
    The fix is to:
    a) grab rcu lock in sys_ioprio_{set,get}() and
    b) avoid grabbing tasklist_lock.
    Discussion in: http://marc.info/?l=linux-kernel&m=128951324702889Signed-off-by: default avatarGreg Thelen <gthelen@google.com>
    Acked-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
    Reviewed-by: default avatarOleg Nesterov <oleg@redhat.com>
    
    Modified by Jens to remove the now redundant inner rcu lock and
    unlock since they are now protected by the outer lock.
    Signed-off-by: default avatarJens Axboe <jaxboe@fusionio.com>
    d69b78ba
ioprio.c 5 KB