Commit 1a6b69b6548c (ARM: gic: add CPU migration support, 2012-04-12) introduced an acquisition of the irq_controller_lock in gic_raise_softirq() which can lead to a spinlock recursion if the gic_arch_extn hooks call into the scheduler (via complete() or wake_up(), etc.). This happens because gic_arch_extn hooks are normally called with the irq_controller_lock held and calling into the scheduler may cause us to call smp_send_reschedule() which will grab the irq_controller_lock again. Here's an example from a vendor kernel (note that the gic_arch_extn hook code here isn't actually in mainline): BUG: spinlock recursion on CPU#0, swapper/0/1 lock: irq_controller_lock+0x0/0x18, .magic: dead4ead, .owner: sw er_cpu: 0 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.14.10-00430-g3d433c4e Call trace: [<ffffffc000087e1c>] dump_backtrace+0x0/0x140 [<ffffffc000087f6c>] show_stack+0x10/0x1c [<ffffffc00064732c>] dump_stack+0x74/0xc4 [<ffffffc0006446c0>] spin_dump+0x78/0x88 [<ffffffc0006446f4>] spin_bug+0x24/0x34 [<ffffffc0000d47d0>] do_raw_spin_lock+0x58/0x148 [<ffffffc00064d398>] _raw_spin_lock_irqsave+0x24/0x38 [<ffffffc0002c9d7c>] gic_raise_softirq+0x2c/0xbc [<ffffffc00008daa4>] smp_send_reschedule+0x34/0x40 [<ffffffc0000c1e94>] try_to_wake_up+0x224/0x288 [<ffffffc0000c1f4c>] default_wake_function+0xc/0x18 [<ffffffc0000ceef0>] __wake_up_common+0x50/0x8c [<ffffffc0000cef3c>] __wake_up_locked+0x10/0x1c [<ffffffc0000cf734>] complete+0x3c/0x5c [<ffffffc0002f0e78>] msm_mpm_enable_irq_exclusive+0x1b8/0x1c8 [<ffffffc0002f0f58>] __msm_mpm_enable_irq+0x4c/0x7c [<ffffffc0002f0f94>] msm_mpm_enable_irq+0xc/0x18 [<ffffffc0002c9bb0>] gic_unmask_irq+0x40/0x7c [<ffffffc0000de5f4>] irq_enable+0x2c/0x48 [<ffffffc0000de65c>] irq_startup+0x4c/0x74 [<ffffffc0000dd2fc>] __setup_irq+0x264/0x3f0 [<ffffffc0000dd5e0>] request_threaded_irq+0xcc/0x11c [<ffffffc0000df254>] devm_request_threaded_irq+0x68/0xb4 [<ffffffc000471520>] msm_iommu_ctx_probe+0x124/0x2d4 [<ffffffc000337374>] platform_drv_probe+0x20/0x54 [<ffffffc00033598c>] driver_probe_device+0x158/0x340 [<ffffffc000335c20>] __driver_attach+0x60/0x90 [<ffffffc000333c9c>] bus_for_each_dev+0x6c/0x8c [<ffffffc000335304>] driver_attach+0x1c/0x28 [<ffffffc000334f14>] bus_add_driver+0x120/0x204 [<ffffffc0003362e4>] driver_register+0xbc/0x10c [<ffffffc000337348>] __platform_driver_register+0x5c/0x68 [<ffffffc00094c478>] msm_iommu_driver_init+0x54/0x7c [<ffffffc0000813ec>] do_one_initcall+0xa4/0x130 [<ffffffc00091d928>] kernel_init_freeable+0x138/0x1dc [<ffffffc000642578>] kernel_init+0xc/0xd4 We really just want to synchronize the sending of an SGI with the update of the gic_cpu_map[], so introduce a new SGI lock that we can use to synchronize the two code paths. Three main events are happening that we have to consider: 1. We're updating the gic_cpu_mask to point to an incoming CPU 2. We're (potentially) sending an SGI to the outgoing CPU 3. We're redirecting any pending SGIs for the outgoing CPU to the incoming CPU. Events 1 and 3 are already ordered within the same CPU by means of program order and use of I/O accessors. Events 1 and 2 don't need to be ordered, but events 2 and 3 do because any SGIs for the outgoing CPU need to be pending before we can redirect them. Synchronize by acquiring a new lock around event 2 and before event 3. Use smp_mb__after_unlock_lock() before event 3 to ensure that event 1 is seen before event 3 on other CPUs that may be executing event 2. Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx> --- Changes since v1: * Move gic_sgi_lock definition below gic_cpu_map[] * Just use spinlock for synchronization instead of over the map update drivers/irqchip/irq-gic.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c index 7c131cf7cc13..00bac4627d2e 100644 --- a/drivers/irqchip/irq-gic.c +++ b/drivers/irqchip/irq-gic.c @@ -81,6 +81,9 @@ static DEFINE_RAW_SPINLOCK(irq_controller_lock); #define NR_GIC_CPU_IF 8 static u8 gic_cpu_map[NR_GIC_CPU_IF] __read_mostly; +/* Synchronize switching CPU interface and sending SGIs */ +static DEFINE_RAW_SPINLOCK(gic_sgi_lock); + /* * Supported arch specific GIC irq extension. * Default make them NULL. @@ -658,7 +661,7 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq) int cpu; unsigned long flags, map = 0; - raw_spin_lock_irqsave(&irq_controller_lock, flags); + raw_spin_lock_irqsave(&gic_sgi_lock, flags); /* Convert our logical CPU mask into a physical one. */ for_each_cpu(cpu, mask) @@ -673,7 +676,7 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq) /* this always happens on GIC0 */ writel_relaxed(map << 16 | irq, gic_data_dist_base(&gic_data[0]) + GIC_DIST_SOFTINT); - raw_spin_unlock_irqrestore(&irq_controller_lock, flags); + raw_spin_unlock_irqrestore(&gic_sgi_lock, flags); } #endif @@ -764,6 +767,15 @@ void gic_migrate_target(unsigned int new_cpu_id) raw_spin_unlock(&irq_controller_lock); + raw_spin_lock(&gic_sgi_lock); + /* + * Ensure that the gic_cpu_map update above is seen in + * gic_raise_softirq() before we redirect any pending SGIs that + * may have been raised for the outgoing CPU (cur_cpu_id) + */ + smp_mb__after_unlock_lock(); + raw_spin_unlock(&gic_sgi_lock); + /* * Now let's migrate and clear any potential SGIs that might be * pending for us (cur_cpu_id). Since GIC_DIST_SGI_PENDING_SET -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
