Subject: 2.6.28-rt on PowerPC

From: Anton Vorontsov <[email-masked]>
Date: Fri, 30 Jan 2009 00:34:29 +0300

Hi Steven,

I know 2.6.28-rt isn't yet ready, but I could not resist to try
it anyway. ;-)

Here are few issues and ways to solve them:

Currently the -rt tree doesn't link for arch/powerpc:

  LD      .tmp_vmlinux1
  arch/powerpc/kernel/built-in.o: In function `show_interrupts':
  (.text+0x27bc): undefined reference to `__call_bad_lock_func'
  arch/powerpc/kernel/built-in.o: In function `show_interrupts':
  (.text+0x28b0): undefined reference to `__call_bad_lock_func'
  make: *** [.tmp_vmlinux1] Error 1

This can be trivially fixed:

diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 838857f..cc7dd12 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -183,7 +183,7 @@ int show_interrupts(struct seq_file *p, void *v)
 
 	if (i < NR_IRQS) {
 		desc = get_irq_desc(i);
-		acquire_lock_irqsave(&desc->lock, flags);
+		spin_lock_irqsave(&desc->lock, flags);
 		action = desc->action;
 		if (!action || !action->handler)
 			goto skip;
@@ -204,7 +204,7 @@ int show_interrupts(struct seq_file *p, void *v)
 			seq_printf(p, ", %s", action->name);
 		seq_putc(p, '\n');
 skip:
-		release_lock_irqrestore(&desc->lock, flags);
+		spin_unlock_irqrestore(&desc->lock, flags);
 	} else if (i == NR_IRQS) {
 #if defined(CONFIG_PPC32) && defined(CONFIG_TAU_INT)
 		if (tau_initialized){

--

While booting, this bug appears:

BUG: sleeping function called from invalid context at kernel/rtmutex.c:683
in_atomic(): 1 [00010001], irqs_disabled(): 1, pid: 1, name: swapper
Call Trace:
[cf82f9a0] [c0008be8] show_stack+0x4c/0x16c (unreliable)
[cf82f9e0] [c001c184] __might_sleep+0xd8/0xf8
[cf82f9f0] [c02b7758] rt_spin_lock+0x30/0x78
[cf82fa00] [c001853c] ipic_mask_irq+0x3c/0xb0
[cf82fa20] [c0054064] handle_level_irq+0x40/0x178
[cf82fa40] [c00068ec] do_IRQ+0x68/0xe0
[cf82fa50] [c0012924] ret_from_except+0x0/0x14
--- Exception: 501 at internal_add_timer+0x4/0xe0

This is trivially solved by converting arch/powerpc/sysdev/ipic.c
back to spinlocks (ipic_lock).

Assuming that converting-back is automatic, there are few other
chained interrupt controllers you might want to convert-back:

arch/powerpc/sysdev/i8259.c (i8259_lock)
arch/powerpc/sysdev/mpic.c (mpic_lock)
arch/powerpc/sysdev/qe_lib/qe_ic.c (qe_ic_lock)

After this, kernel boots up to the userspace, but then bugs in the
middle (note: this is NFS boot, network activity etc.)...

INIT: version 2.86 booting
Starting the hotplug events dispatcher: udevd.
Synthesizing the initial hotplug events...done.
Waiting for /dev to be fully populated...done.
Activating swap...done.
Remounting root filesystem...done.
Checking all file systems: fsck
fsck 1.40 (29-Jun-2007)
Checking SELinux contexts: selinux-basics.
Starting network interfaces: done.
Starting portmap daemon....
Cleaning: /tmp /var/lock /var/run done.
Setting pseudo-terminal access permissions...done.
Updating /etc/motd...done.
INIT: Entering runlevel: 3
Starting irqbalance.
Starting system log daemon: syslogd
BUG: sleeping function called from invalid context at kernel/rtmutex.c:683
in_atomic(): 1 [00000100], irqs_disabled(): 0, pid: 7, name: sirq-net-rx/0
Call Trace:
[cf84bc20] [c0008be8] show_stack+0x4c/0x16c (unreliable)
[cf84bc60] [c001c194] __might_sleep+0xd8/0xf8
[cf84bc70] [c02b7768] rt_spin_lock+0x30/0x78
[cf84bc80] [c00800e0] kmem_cache_alloc+0x50/0x17c
[cf84bcb0] [c02568a4] ip_append_data+0x974/0x978
[cf84bd30] [c027aa0c] icmp_push_reply+0x54/0x128
[cf84bd50] [c027b59c] icmp_send+0x284/0x380
[cf84be40] [c0277328] __udp4_lib_rcv+0x3d4/0x5a0
[cf84bea0] [c0253208] ip_local_deliver_finish+0x74/0x128
[cf84bec0] [c0252fd0] ip_rcv_finish+0x148/0x30c
[cf84bf00] [c0236774] netif_receive_skb+0x21c/0x2e8
[cf84bf30] [c0238ecc] process_backlog+0x98/0x138
[cf84bf60] [c0238b24] net_rx_action+0xd4/0x198
[cf84bf90] [c002989c] ksoftirqd+0x108/0x23c
[cf84bfd0] [c003c918] kthread+0x48/0x84
[cf84bff0] [c00120b0] kernel_thread+0x4c/0x68
BUG: scheduling while atomic: sirq-net-rx/0/7/0x10000101, CPU#0
Modules linked in:
Call Trace:
[cf84bee0] [c0008be8] show_stack+0x4c/0x16c (unreliable)
[cf84bf20] [c001e418] __schedule_bug+0x6c/0x80
[cf84bf30] [c02b5fdc] schedule+0x2e8/0x31c
[cf84bf70] [c001e460] __cond_resched+0x34/0x60
[cf84bf80] [c02b6348] _cond_resched+0x50/0x58
[cf84bf90] [c00298b8] ksoftirqd+0x124/0x23c
[cf84bfd0] [c003c918] kthread+0x48/0x84
[cf84bff0] [c00120b0] kernel_thread+0x4c/0x68

And now this looks like not PowerPC specific... Converting mm/slab.c
back to spinlocks results in another, but similar bug in anther mm
routine:

BUG: sleeping function called from invalid context at kernel/rtmutex.c:683
in_atomic(): 1 [00000001], irqs_disabled(): 0, pid: 1003, name: net.agent
Call Trace:
[cf057c40] [c0008be8] show_stack+0x4c/0x16c (unreliable)
[cf057c80] [c001c194] __might_sleep+0xd8/0xf8
[cf057c90] [c02b7768] rt_spin_lock+0x30/0x78
[cf057ca0] [c005d0ec] free_hot_cold_page+0xf8/0x35c
[cf057cc0] [c007f0b0] kmem_freepages+0xd8/0x134
[cf057cd0] [c007f620] slab_destroy+0x38/0xe0
[cf057cf0] [c007f814] free_block+0x14c/0x158
[cf057d30] [c007f174] cache_flusharray+0x68/0x150
[cf057d60] [c007f4fc] kmem_cache_free+0x110/0x140
[cf057d80] [c006eb04] remove_vma+0x78/0xc0
[cf057d90] [c006eccc] exit_mmap+0x180/0x208
[cf057dc0] [c00210c8] mmput+0x64/0x114
[cf057de0] [c008b580] exec_mmap+0xd8/0x1b4
[cf057e10] [c008b7c4] flush_old_exec+0x50/0x1d0
[cf057e40] [c00c2fac] load_elf_binary+0x2b0/0x96c
[cf057eb0] [c008ad6c] search_binary_handler+0xf4/0x31c
[cf057ef0] [c008c220] do_execve+0x1b4/0x1ec
[cf057f20] [c000983c] sys_execve+0x50/0x7c
[cf057f40] [c001228c] ret_from_syscall+0x0/0x38
--- Exception: c01 at 0xfeab104
    LR = 0x10024540

..proves that "convert-back" trick isn't panacea. ;-) So, before
I'll dig into this.. is this known issue? Any ideas of proper
fixing?

FWIW, following options enabled:

CONFIG_NO_HZ=y
CONFIG_HIGH_RES_TIMERS=y
CONFIG_PREEMPT_RT=y
CONFIG_PREEMPT=y
CONFIG_PREEMPT_RCU=y
CONFIG_PREEMPT_SOFTIRQS=y
CONFIG_PREEMPT_HARDIRQS=y
CONFIG_DEBUG_FS=y
CONFIG_DEBUG_KERNEL=y
CONFIG_SCHED_DEBUG=y
CONFIG_DEBUG_RT_MUTEXES=y
CONFIG_DEBUG_PI_LIST=y
CONFIG_DEBUG_SPINLOCK=y
CONFIG_DEBUG_SPINLOCK_SLEEP=y
CONFIG_DEBUG_BUGVERBOSE=y
CONFIG_SLAB=y
CONFIG_SLABINFO=y
# CONFIG_HIGHMEM is not set

Thanks,

p.s. Btw, having the convert-back script in scripts/ would be
useful. Could not find it anywhere.

-- 
Anton Vorontsov
email: [email-masked]
irc://irc.freenode.net/bd2