Re: CPU hotplug and IRQ affinity with 2.6.24-rt1

["Gregory Haskins" <ghaskins@novell.com>]

Hi Daniel,

  See inline...

>>> On Mon, Feb 4, 2008 at  9:51 PM, in message
<20080205025144.GA31774@dwalker1.mvista.com>, Daniel Walker
<dwalker@dwalker1.mvista.com> wrote: 
> On Mon, Feb 04, 2008 at 03:35:13PM -0800, Max Krasnyanskiy wrote:
>> This is just an FYI. As part of the "Isolated CPU extensions" thread Daniel 
> suggest for me
>> to check out latest RT kernels. So I did or at least tried to and 
> immediately spotted a couple
>> of issues.
>>
>> The machine I'm running it on is:
>> 	HP xw9300, Dual Opteron, NUMA
>>
>> It looks like with -rt kernel IRQ affinity masks are ignored on that 
>> system. ie I write 1 to lets say /proc/irq/23/smp_affinity but the 
>> interrupts keep coming to CPU1. Vanilla 2.6.24 does not have that issue.
> 
> I tried this, and it works according to /proc/interrupts .. Are you
> looking at the interrupt threads affinity?
> 
>> Also the first thing I tried was to bring CPU1 off-line. Thats the fastest 
>> way to get irqs, soft-irqs, timers, etc of a CPU. But the box hung 
>> completely. It also managed to mess up my ext3 filesystem to the point 
>> where it required manual fsck (have not see that for a couple of
>> years now). I tried the same thing (ie echo 0 > 
>> /sys/devices/cpu/cpu1/online) from the console. It hang again with the 
>> message that looked something like:
>> 	CPU1 is now off-line
>> 	Thread IRQ-23 is on CPU1 ...
> 
> I get the following when I tried it,
> 
> BUG: sleeping function called from invalid context bash(5126) at
> kernel/rtmutex.c:638
> in_atomic():1 [00000001], irqs_disabled():1
> Pid: 5126, comm: bash Not tainted 2.6.24-rt1 #1
>  [<c010506b>] show_trace_log_lvl+0x1d/0x3a
>  [<c01059cd>] show_trace+0x12/0x14
>  [<c0106151>] dump_stack+0x6c/0x72
>  [<c011d153>] __might_sleep+0xe8/0xef
>  [<c03b2326>] __rt_spin_lock+0x24/0x59
>  [<c03b2363>] rt_spin_lock+0x8/0xa
>  [<c0165b2f>] kfree+0x2c/0x8d

Doh!  This is my bug.  Ill have to come up with a good way to free that memory under atomic, or do this another way.  Stay tuned.

>  [<c011eacb>] rq_attach_root+0x67/0xba
>  [<c01209ae>] cpu_attach_domain+0x2b6/0x2f7
>  [<c0120a12>] detach_destroy_domains+0x23/0x37
>  [<c0121368>] update_sched_domains+0x2d/0x40
>  [<c013b482>] notifier_call_chain+0x2b/0x55
>  [<c013b4d9>] __raw_notifier_call_chain+0x19/0x1e
>  [<c01420d3>] _cpu_down+0x84/0x24c
>  [<c01422c3>] cpu_down+0x28/0x3a
>  [<c029f59e>] store_online+0x27/0x5a
>  [<c029c9dc>] sysdev_store+0x20/0x25
>  [<c019a695>] sysfs_write_file+0xad/0xde
>  [<c0169929>] vfs_write+0x82/0xb8
>  [<c0169e2a>] sys_write+0x3d/0x61
>  [<c0104072>] sysenter_past_esp+0x5f/0x85
>  =======================
> ---------------------------
> | preempt count: 00000001 ]
> | 1-level deep critical section nesting:
> ----------------------------------------
> .. [<c03b25e2>] .... __spin_lock_irqsave+0x14/0x3b
> .....[<c011ea76>] ..   ( <= rq_attach_root+0x12/0xba)
> 
> Which is clearly a problem .. 
> 
> (I added linux-rt-users to the CC)
> 
> Daniel
> -
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