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

[Stephen Boyd <sboyd@codeaurora.org>]

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.

Cc: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
---
 drivers/irqchip/irq-gic.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
index 7c131cf7cc13..824c1e2ac403 100644
--- a/drivers/irqchip/irq-gic.c
+++ b/drivers/irqchip/irq-gic.c
@@ -72,6 +72,8 @@ struct gic_chip_data {
 };
 
 static DEFINE_RAW_SPINLOCK(irq_controller_lock);
+/* Synchronize switching CPU interface and sending SGIs */
+static DEFINE_RAW_SPINLOCK(gic_sgi_lock);
 
 /*
  * The GIC mapping of CPU interfaces does not necessarily match
@@ -658,7 +660,7 @@ 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 +675,7 @@ 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
 
@@ -742,6 +744,7 @@ void gic_migrate_target(unsigned int new_cpu_id)
 	cur_target_mask = 0x01010101 << cur_cpu_id;
 	ror_val = (cur_cpu_id - new_cpu_id) & 31;
 
+	raw_spin_lock(&gic_sgi_lock);
 	raw_spin_lock(&irq_controller_lock);
 
 	/* Update the target interface for this logical CPU */
@@ -763,6 +766,7 @@ void gic_migrate_target(unsigned int new_cpu_id)
 	}
 
 	raw_spin_unlock(&irq_controller_lock);
+	raw_spin_unlock(&gic_sgi_lock);
 
 	/*
 	 * Now let's migrate and clear any potential SGIs that might be
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
hosted by The Linux Foundation