[PATCH v2 0/1] mmc: host: meson-gx-mmc: fix possible deadlock condition for preempt_rt

[Brad Harper <bjharper@gmail.com>]

This is a updated experiamental patch for review following discussions
with Jerome / Sebastian regarding the usage of threadded interupts in
meson-gx-mmc.  I don't have a complete understanding or am I a kernel
developer but this is my best efforts attempt to address this issue.

Also thanks to both of of them for opening up the discussions and 
Kevin for pointing me in the right direction for patch formatting. 

Force threaded interrupts for meson_mmc_irq to prevent possible deadlock
condition during mmc operations when using preempt_rt with 5.9.0-rc3-rt3
patches on arm64.

Using meson-gx-mmc with an emmc device on Hardkernel Odroid N2+
configured with preempt_rt resulted in the soc becoming unresponsive.  
With lock checking enabled the below inconsistent lock state was 
observed during boot.

After some discussions with tglx in IRC #linux-rt a patch was suggested
to remove IRQF_ONESHOT from request_threaded_irq.
This has been tested and confirmed by me to resolve both the 
unresponsive soc and the inconsistent lock state warning when using 
5.9.0-rc3-rt3 on arm64 Odroid N2+.

Further review and testing is required to ensure there are no adverse 
impacts or concerns and that is the correct method to resolve the 
problem.  I will continue to test on various amlogic devices with both 
standard mainline low latency kernel and preempt_rt kernel with -rt 
patches.

Changes since v1:
- Add spinlock_t lock to meson_host structure
- Add spin_lock_init to driver probe for the host lock to ensure the 
  irq will not attempt to fire again if the threaded irq component
  is not complete


[    7.858446] ================================
[    7.858448] WARNING: inconsistent lock state
[    7.858450] 5.9.0-rc3-rt3+ #33 Not tainted
[    7.858453] --------------------------------
[    7.858456] inconsistent {IN-HARDIRQ-R} -> {HARDIRQ-ON-W} usage.
[    7.858459] swapper/0/1 [HC0[0]:SC0[0]:HE1:SE1] takes:
[    7.858465] ffff80001219f4d8 (&trig->leddev_list_lock){+?.+}-{0:0}, at: led_trigger_set+0x104/0x270
[    7.858482] {IN-HARDIRQ-R} state was registered at:
[    7.858484]   lock_acquire+0xec/0x468
[    7.858491]   rt_read_lock+0xb0/0x108
[    7.858497]   led_trigger_event+0x34/0x88
[    7.858501]   mmc_request_done+0x3f0/0x450
[    7.858505]   meson_mmc_irq+0x284/0x378
[    7.858511]   __handle_irq_event_percpu+0xcc/0x4a8
[    7.858515]   handle_irq_event_percpu+0x60/0xb0
[    7.858519]   handle_irq_event+0x50/0x108
[    7.858522]   handle_fasteoi_irq+0xd0/0x180
[    7.858527]   generic_handle_irq+0x38/0x50
[    7.858530]   __handle_domain_irq+0x6c/0xc8
[    7.858533]   gic_handle_irq+0x5c/0xb8
[    7.858537]   el1_irq+0xbc/0x180
[    7.858540]   arch_cpu_idle+0x28/0x38
[    7.858544]   default_idle_call+0x90/0x3f0
[    7.858547]   do_idle+0x250/0x268
[    7.858551]   cpu_startup_entry+0x2c/0x78
[    7.858554]   rest_init+0x1b0/0x284
[    7.858559]   arch_call_rest_init+0x18/0x24
[    7.858565]   start_kernel+0x550/0x588
[    7.858569] irq event stamp: 1925495
[    7.858571] hardirqs last  enabled at (1925495): [<ffff8000111e3ba4>] _raw_spin_unlock_irqrestore+0xa4/0xb0
[    7.858576] hardirqs last disabled at (1925494): [<ffff8000111e3c58>] _raw_spin_lock_irqsave+0xa8/0xb8
[    7.858580] softirqs last  enabled at (1857856): [<ffff80001024705c>] bdi_register_va+0x114/0x368
[    7.858586] softirqs last disabled at (1857849): [<ffff80001024705c>] bdi_register_va+0x114/0x368
[    7.858590] 
               other info that might help us debug this:
[    7.858592]  Possible unsafe locking scenario:

[    7.858594]        CPU0
[    7.858595]        ----
[    7.858597]   lock(&trig->leddev_list_lock);
[    7.858600]   <Interrupt>
[    7.858602]     lock(&trig->leddev_list_lock);
[    7.858604] 
                *** DEADLOCK ***

[    7.858606] 3 locks held by swapper/0/1:
[    7.858609]  #0: ffff80001219eb30 (leds_list_lock){++++}-{0:0}, at: led_trigger_register+0xf4/0x1c0
[    7.858619]  #1: ffff0000b0696a70 (&led_cdev->trigger_lock){+.+.}-{0:0}, at: led_trigger_register+0x134/0x1c0
[    7.858629]  #2: ffff800011fb83d0 (rcu_read_lock){....}-{1:2}, at: rt_write_lock+0x8/0x108
[    7.858637] 
               stack backtrace:
[    7.858640] CPU: 5 PID: 1 Comm: swapper/0 Not tainted 5.9.0-rc3-rt3+ #33
[    7.858643] Hardware name: Hardkernel ODROID-N2Plus (DT)
[    7.858646] Call trace:
[    7.858647]  dump_backtrace+0x0/0x1e8
[    7.858650]  show_stack+0x20/0x30
[    7.858653]  dump_stack+0xf0/0x164
[    7.858659]  print_usage_bug+0x2b4/0x2c0
[    7.858662]  mark_lock+0x2e8/0x360
[    7.858665]  __lock_acquire+0x238/0x1858
[    7.858669]  lock_acquire+0xec/0x468
[    7.858672]  rt_write_lock+0xb0/0x108
[    7.858675]  led_trigger_set+0x104/0x270
[    7.858678]  led_trigger_register+0x180/0x1c0
[    7.858681]  heartbeat_trig_init+0x28/0x5c
[    7.858686]  do_one_initcall+0x90/0x4bc
[    7.858690]  kernel_init_freeable+0x2cc/0x338
[    7.858694]  kernel_init+0x1c/0x11c
[    7.858697]  ret_from_fork+0x10/0x34

Brad Harper (1):
  mmc: host: meson-gx-mmc: fix possible deadlock condition for
    preempt_rt

 drivers/mmc/host/meson-gx-mmc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

-- 
2.20.1