Re: [PATCH, RFC] improved hacks to allow -rt to run kernbench on POWER

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

> And here is an updated patch.  There has to be a better way than the
> #ifdef, but I need the two local variables, and breaking the intervening
> code out into a separate function didn't quite seem right either.
> 
> Thoughts?

Nothing comes to mind right now...

> This one does only one oops during boot-up, which I will start looking
> at:
> 
> BUG: sleeping function called from invalid context ifconfig(994) at kernel/rtmutex.c:637
> in_atomic():1 [00000002], irqs_disabled():1
> Call Trace:
> [c0000000ff49f030] [c000000000010028] .show_stack+0x6c/0x1a0 (unreliable)
> [c0000000ff49f0d0] [c00000000004f8b4] .__might_sleep+0x11c/0x138
> [c0000000ff49f150] [c00000000039c920] .__rt_spin_lock+0x38/0xa0
> [c0000000ff49f1d0] [c0000000000cf8e8] .kmem_cache_alloc+0x68/0x184
> [c0000000ff49f270] [c0000000001f7534] .radix_tree_node_alloc+0x3c/0x104
> [c0000000ff49f300] [c0000000001f8418] .radix_tree_insert+0x19c/0x324
> [c0000000ff49f3c0] [c00000000000b758] .irq_radix_revmap+0x140/0x178
> [c0000000ff49f470] [c000000000044aec] .xics_startup+0x30/0x54
> [c0000000ff49f500] [c0000000000997f4] .setup_irq+0x254/0x320
> [c0000000ff49f5b0] [c000000000099984] .request_irq+0xc4/0x114
> [c0000000ff49f660] [d00000000079b194] .e1000_open+0xdc/0x1b8 [e1000]
> [c0000000ff49f6f0] [c00000000030a840] .dev_open+0x94/0x110
> [c0000000ff49f790] [c00000000030a69c] .dev_change_flags+0x110/0x220
> [c0000000ff49f830] [c00000000036a0a8] .devinet_ioctl+0x2cc/0x764
> [c0000000ff49f930] [c00000000036a6a8] .inet_ioctl+0xe8/0x138
> [c0000000ff49f9b0] [c0000000002f9acc] .sock_ioctl+0x2c8/0x314
> [c0000000ff49fa50] [c0000000000e6dec] .do_ioctl+0x5c/0xf0
> [c0000000ff49faf0] [c0000000000e731c] .vfs_ioctl+0x49c/0x4d4
> [c0000000ff49fba0] [c0000000000e73ec] .sys_ioctl+0x98/0xe0
> [c0000000ff49fc50] [c000000000117944] .dev_ifsioc+0x1e0/0x46c
> [c0000000ff49fd40] [c00000000011e1d4] .compat_sys_ioctl+0x40c/0x4a0
> [c0000000ff49fe30] [c00000000000852c] syscall_exit+0x0/0x40

The radix tree is used by the powerpc IRQ subsystem with some hand-made
locking that involves per-cpu variables among others, you may want to
have a look at arch/powerpc/kernel/irq.c ... It should all be GFP_ATOMIC
though, but if -rt can't cope with even GFP_ATOMIC when preempt is off,
then we have a deeper problem (the allocation of the page for RCU in
freeing page tables is another one that will GFP_ATOMIC in
non-preemptible context afaik).

Ben.