Stephen, On Wed, Aug 13, 2014 at 06:57:18AM -0700, 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 | 23 +++++++++++++++++++++-- > 1 file changed, 21 insertions(+), 2 deletions(-) Applied to irqchip/urgent with Nico's Ack. thx, Jason. -- 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
