On 2010-11-12 08:32, Greg Thelen wrote: > 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=128951324702889 Thanks Greg, applied. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html