On 13/08/14 01:54, Stephen Boyd wrote:
> 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@xxxxxxxxxx>
> Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
> ---
> 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
I really like this patch.
After I've reviewed things properly I will probably propose a patch to
change gic_sgi_lock to a raw_rwlock_t. My motivation is that I think
that using a rwlock renders it safe to call smp_send_reschedule() from
FIQ handlers.
No need to wait for me though. The change is good as it is:
Reviewed-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> +
> /*
> * 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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