ioprio: grab rcu_read_lock in sys_ioprio_{set,get}()
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
Signed-off-by: Greg Thelen <gthelen@google.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Oleg 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: Jens Axboe <jaxboe@fusionio.com>
1 file changed