Hi , here is a respin of the patches I posted last week for the RT kernel now targeted for mainline (http://lkml.org/lkml/2008/7/24/98). Thomas, steven, a note for you at the end. The goal of this patchset is to simplify the locking constraints on the radix tree used for IRQ reverse mapping on the pSeries machines and provide lockless access to this tree. This also solves the following BUG under preempt-rt: BUG: sleeping function called from invalid context swapper(1) at kernel/rtmutex.c:739 in_atomic():1 [00000002], irqs_disabled():1 Call Trace: [c0000001e20f3340] [c000000000010370] .show_stack+0x70/0x1bc (unreliable) [c0000001e20f33f0] [c000000000049380] .__might_sleep+0x11c/0x138 [c0000001e20f3470] [c0000000002a2f64] .__rt_spin_lock+0x3c/0x98 [c0000001e20f34f0] [c0000000000c3f20] .kmem_cache_alloc+0x68/0x184 [c0000001e20f3590] [c000000000193f3c] .radix_tree_node_alloc+0xf0/0x144 [c0000001e20f3630] [c000000000195190] .radix_tree_insert+0x18c/0x2fc [c0000001e20f36f0] [c00000000000c710] .irq_radix_revmap+0x1a4/0x1e4 [c0000001e20f37b0] [c00000000003b3f0] .xics_startup+0x30/0x54 [c0000001e20f3840] [c00000000008b864] .setup_irq+0x26c/0x370 [c0000001e20f38f0] [c00000000008ba68] .request_irq+0x100/0x158 [c0000001e20f39a0] [c0000000001ee9c0] .hvc_open+0xb4/0x148 [c0000001e20f3a40] [c0000000001d72ec] .tty_open+0x200/0x368 [c0000001e20f3af0] [c0000000000ce928] .chrdev_open+0x1f4/0x25c [c0000001e20f3ba0] [c0000000000c8bf0] .__dentry_open+0x188/0x2c8 [c0000001e20f3c50] [c0000000000c8dec] .do_filp_open+0x50/0x70 [c0000001e20f3d70] [c0000000000c8e8c] .do_sys_open+0x80/0x148 [c0000001e20f3e20] [c00000000000928c] .init_post+0x4c/0x100 [c0000001e20f3ea0] [c0000000003c0e0c] .kernel_init+0x428/0x478 [c0000001e20f3f90] [c000000000027448] .kernel_thread+0x4c/0x68 The root cause of this bug lies in the fact that the XICS interrupt controller uses a radix tree for its reverse irq mapping and that we cannot allocate the tree nodes (even GFP_ATOMIC) with preemption disabled. In fact, we have 2 nested preemption disabling when we want to allocate a new node: - setup_irq() does a spin_lock_irqsave() before calling xics_startup() which then calls irq_radix_revmap() to insert a new node in the tree - irq_radix_revmap() also does a spin_lock_irqsave() (in irq_radix_wrlock()) before the radix_tree_insert() Also, if an IRQ gets registered before the tree is initialized (namely the IPI), it will be inserted into the tree in interrupt context once the tree have been initialized, hence the need for a spin_lock_irqsave() in the insertion path. This serie is split into 3 patches: - The first patch moves the initialization of the radix tree earlier in the boot process before any IRQ gets registered, but after the mm is up. - The second patch splits irq_radix_revmap() into its 2 components: one for lookup and one for insertion into the radix tree. - And finally, the third patch makes the radix tree fully lockless on the lookup side. Here is the diffstat for the whole patchset: arch/powerpc/kernel/irq.c | 134 ++++++++------------------------- arch/powerpc/platforms/pseries/smp.c | 1 + arch/powerpc/platforms/pseries/xics.c | 11 +-- include/asm-powerpc/irq.h | 24 +++++- 4 files changed, 58 insertions(+), 112 deletions(-) Thomas, Steven, the first 2 patches can be applied seamlessly to 2.6.26-rt1 with offsets, the third patch has a trivial to fix reject in arch/powerpc/kernel/irq.c because the irq_big_lock is changed to a raw spinlock in preempt-rt. If you want those patches for RT, just flag me, I have those sitting on my test box. Thanks, Sebastien. -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
