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
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