[PATCH v3] irqchip: gic: Allow gic_arch_extn hooks to call into scheduler

[sboyd@codeaurora.org (Stephen Boyd)]

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. We put this all behind the b.L switcher config
option so that if we're not using this feature we don't have to
acquire any locks at all in the IPI path.

Cc: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---
 drivers/irqchip/irq-gic.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
index 7c131cf7cc13..c1dc65209899 100644
--- a/drivers/irqchip/irq-gic.c
+++ b/drivers/irqchip/irq-gic.c
@@ -81,6 +81,11 @@ static DEFINE_RAW_SPINLOCK(irq_controller_lock);
 #define NR_GIC_CPU_IF 8
 static u8 gic_cpu_map[NR_GIC_CPU_IF] __read_mostly;
 
+#ifdef CONFIG_BL_SWITCHER
+/* Synchronize switching CPU interface and sending SGIs */
+static DEFINE_RAW_SPINLOCK(gic_sgi_lock);
+#endif
+
 /*
  * Supported arch specific GIC irq extension.
  * Default make them NULL.
@@ -656,9 +661,12 @@ static void __init gic_pm_init(struct gic_chip_data *gic)
 static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq)
 {
 	int cpu;
-	unsigned long flags, map = 0;
+	unsigned long map = 0;
+#ifdef CONFIG_BL_SWITCHER
+	unsigned long flags;
 
-	raw_spin_lock_irqsave(&irq_controller_lock, flags);
+	raw_spin_lock_irqsave(&gic_sgi_lock, flags);
+#endif
 
 	/* Convert our logical CPU mask into a physical one. */
 	for_each_cpu(cpu, mask)
@@ -673,7 +681,9 @@ 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);
+#ifdef CONFIG_BL_SWITCHER
+	raw_spin_unlock_irqrestore(&gic_sgi_lock, flags);
+#endif
 }
 #endif
 
@@ -764,6 +774,15 @@ 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
-- 
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