[BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM

[Marc.Zyngier@arm.com (Marc Zyngier)]

On Thu, 2011-05-26 at 18:09 +0200, Peter Zijlstra wrote:
> On Thu, 2011-05-26 at 17:59 +0200, Peter Zijlstra wrote:
> > On Thu, 2011-05-26 at 17:45 +0200, Oleg Nesterov wrote:
> > > Stupid question. Can't we fix this problem if we do
> > > 
> > >         -       if (p == current)
> > >         +       if (cpu == raw_smp_processor_id())
> > > 
> > > ?
> > > 
> > > I forgot the rules... but iirc task_cpu(p) can't be changed under us?
> > 
> > Easy enough to test.. brain gave out again,. hold on ;-)
> 
> The below seems to run all-right so far, I'll let it run for a while.

Just got the following:

INFO: task kjournald:904 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kjournald       D c0284c88     0   904      2 0x00000000
[<c0284c88>] (schedule+0x54c/0x620) from [<c0284dd8>] (io_schedule+0x7c/0xac)
[<c0284dd8>] (io_schedule+0x7c/0xac) from [<c00dc1c0>] (sleep_on_buffer+0x8/0x10)
[<c00dc1c0>] (sleep_on_buffer+0x8/0x10) from [<c02854ac>] (__wait_on_bit+0x54/0x9c)
[<c02854ac>] (__wait_on_bit+0x54/0x9c) from [<c028556c>] (out_of_line_wait_on_bit+0x78/0x84)
[<c028556c>] (out_of_line_wait_on_bit+0x78/0x84) from [<c014bc4c>] (journal_commit_transaction+0x734/0x13f4)
[<c014bc4c>] (journal_commit_transaction+0x734/0x13f4) from [<c014f598>] (kjournald+0xb8/0x210)
[<c014f598>] (kjournald+0xb8/0x210) from [<c0066320>] (kthread+0x80/0x88)
[<c0066320>] (kthread+0x80/0x88) from [<c002ea14>] (kernel_thread_exit+0x0/0x8)

	M.
-- 
Reality is an implementation detail.