This is a note to let you know that I've just added the patch titled
sched: suppress RCU lockdep splat in task_fork_fair
to the 2.6.32-longterm tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/longterm/longterm-queue-2.6.32.git;a=summary
The filename of the patch is:
0007-sched-suppress-RCU-lockdep-splat-in-task_fork_fair.patch
and it can be found in the queue-2.6.32 subdirectory.
If you, or anyone else, feels it should not be added to the 2.6.32 longterm
tree,
please let <[email protected]> know about it.
>From 6c03e4c4ef4c5c1707f78a0c6bccbf4bd79bad35 Mon Sep 17 00:00:00 2001
From: Paul E. McKenney <[email protected]>
Date: Thu, 10 Feb 2011 10:22:08 +0100
Subject: sched: suppress RCU lockdep splat in task_fork_fair
Commit: b0a0f667a349247bd7f05f806b662a25653822bc upstream
> ===================================================
> [ 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 <[email protected]
Signed-off-by: Paul E. McKenney <[email protected]>
Tested-by: Ben Greear <[email protected]
Signed-off-by: Mike Galbraith <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
kernel/sched_fair.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1992,8 +1992,11 @@ static void task_fork_fair(struct task_s
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);
Patches currently in longterm-queue-2.6.32 which might be from
[email protected] are
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