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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-10-06 17:32:51 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-10-07 10:40:50 -0700
commitb0a0f667a349247bd7f05f806b662a25653822bc (patch)
tree90f9e4221e348ece7d211f3039a1b7281f0391e8 /kernel/sched_fair.c
parent1144182a8757f2a1f909f0c592898aaaf80884fc (diff)
downloadlinux-b0a0f667a349247bd7f05f806b662a25653822bc.tar.bz2
sched: suppress RCU lockdep splat in task_fork_fair
> =================================================== > [ INFO: suspicious rcu_dereference_check() usage. ] > --------------------------------------------------- > /home/greearb/git/linux.wireless-testing/kernel/sched.c:618 invoked rcu_dereference_check() without protection! > > other info that might help us debug this: > > rcu_scheduler_active = 1, debug_locks = 1 > 1 lock held by ifup/23517: > #0: (&rq->lock){-.-.-.}, at: [<c042f782>] task_fork_fair+0x3b/0x108 > > stack backtrace: > Pid: 23517, comm: ifup Not tainted 2.6.36-rc6-wl+ #5 > Call Trace: > [<c075e219>] ? printk+0xf/0x16 > [<c0455842>] lockdep_rcu_dereference+0x74/0x7d > [<c0426854>] task_group+0x6d/0x79 > [<c042686e>] set_task_rq+0xe/0x57 > [<c042f79e>] task_fork_fair+0x57/0x108 > [<c042e965>] sched_fork+0x82/0xf9 > [<c04334b3>] copy_process+0x569/0xe8e > [<c0433ef0>] do_fork+0x118/0x262 > [<c076302f>] ? do_page_fault+0x16a/0x2cf > [<c044b80c>] ? up_read+0x16/0x2a > [<c04085ae>] sys_clone+0x1b/0x20 > [<c04030a5>] ptregs_clone+0x15/0x30 > [<c0402f1c>] ? sysenter_do_call+0x12/0x38 Here a newly created task is having its runqueue assigned. The new task is not yet on the tasklist, so cannot go away. This is therefore a false positive, suppress with an RCU read-side critical section. Reported-by: Ben Greear <greearb@candelatech.com Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Ben Greear <greearb@candelatech.com
Diffstat (limited to 'kernel/sched_fair.c')
-rw-r--r--kernel/sched_fair.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index db3f674ca49d..5f996d36ac5d 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -3751,8 +3751,11 @@ static void task_fork_fair(struct task_struct *p)
update_rq_clock(rq);
- if (unlikely(task_cpu(p) != this_cpu))
+ if (unlikely(task_cpu(p) != this_cpu)) {
+ rcu_read_lock();
__set_task_cpu(p, this_cpu);
+ rcu_read_unlock();
+ }
update_curr(cfs_rq);