Re: [Intel-gfx] [PATCH] drm/i915: Avoid circular locking dependency when flush delayed work on gt reset

[Andrzej Hajda]

On 06.06.2023 05:00, Zhanjun Dong wrote:

This attemps to avoid circular locing dependency between flush delayed work and 
intel_gt_reset.

WARNING: possible circular locking dependency detected
6.4.0-rc1-drmtip_1340-g31e3463b0edb+ #1 Not tainted
------------------------------------------------------
kms_pipe_crc_ba/6415 is trying to acquire lock:
ffff88813e6cc640 
((work_completion)(&(&guc->timestamp.work)->work)){+.+.}-{0:0}, at: 
__flush_work+0x42/0x530

but task is already holding lock:
ffff88813e6cce90 (&gt->reset.mutex){+.+.}-{3:3}, at: intel_gt_reset+0x19e/0x470 
[i915]

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (&gt->reset.mutex){+.+.}-{3:3}:
         lock_acquire+0xd8/0x2d0
         i915_gem_shrinker_taints_mutex+0x31/0x50 [i915]
         intel_gt_init_reset+0x65/0x80 [i915]
         intel_gt_common_init_early+0xe1/0x170 [i915]
         intel_root_gt_init_early+0x48/0x60 [i915]
         i915_driver_probe+0x671/0xcb0 [i915]
         i915_pci_probe+0xdc/0x210 [i915]
         pci_device_probe+0x95/0x120
         really_probe+0x164/0x3c0
         __driver_probe_device+0x73/0x160
         driver_probe_device+0x19/0xa0
         __driver_attach+0xb6/0x180
         bus_for_each_dev+0x77/0xd0
         bus_add_driver+0x114/0x210
         driver_register+0x5b/0x110
         __pfx_vgem_open+0x3/0x10 [vgem]
         do_one_initcall+0x57/0x270
         do_init_module+0x5f/0x220
         load_module+0x1ca4/0x1f00
         __do_sys_finit_module+0xb4/0x130
         do_syscall_64+0x3c/0x90
         entry_SYSCALL_64_after_hwframe+0x72/0xdc

-> #2 (fs_reclaim){+.+.}-{0:0}:
         lock_acquire+0xd8/0x2d0
         fs_reclaim_acquire+0xac/0xe0
         kmem_cache_alloc+0x32/0x260
         i915_vma_instance+0xb2/0xc60 [i915]
         i915_gem_object_ggtt_pin_ww+0x175/0x370 [i915]
         vm_fault_gtt+0x22d/0xf60 [i915]
         __do_fault+0x2f/0x1d0
         do_pte_missing+0x4a/0xd20
         __handle_mm_fault+0x5b0/0x790
         handle_mm_fault+0xa2/0x230
         do_user_addr_fault+0x3ea/0xa10
         exc_page_fault+0x68/0x1a0
         asm_exc_page_fault+0x26/0x30

-> #1 (&gt->reset.backoff_srcu){++++}-{0:0}:
         lock_acquire+0xd8/0x2d0
         _intel_gt_reset_lock+0x57/0x330 [i915]
         guc_timestamp_ping+0x35/0x130 [i915]
         process_one_work+0x250/0x510
         worker_thread+0x4f/0x3a0
         kthread+0xff/0x130
         ret_from_fork+0x29/0x50

-> #0 ((work_completion)(&(&guc->timestamp.work)->work)){+.+.}-{0:0}:
         check_prev_add+0x90/0xc60
         __lock_acquire+0x1998/0x2590
         lock_acquire+0xd8/0x2d0
         __flush_work+0x74/0x530
         __cancel_work_timer+0x14f/0x1f0
         intel_guc_submission_reset_prepare+0x81/0x4b0 [i915]
         intel_uc_reset_prepare+0x9c/0x120 [i915]
         reset_prepare+0x21/0x60 [i915]
         intel_gt_reset+0x1dd/0x470 [i915]
         intel_gt_reset_global+0xfb/0x170 [i915]
         intel_gt_handle_error+0x368/0x420 [i915]
         intel_gt_debugfs_reset_store+0x5c/0xc0 [i915]
         i915_wedged_set+0x29/0x40 [i915]
         simple_attr_write_xsigned.constprop.0+0xb4/0x110
         full_proxy_write+0x52/0x80
         vfs_write+0xc5/0x4f0
         ksys_write+0x64/0xe0
         do_syscall_64+0x3c/0x90
         entry_SYSCALL_64_after_hwframe+0x72/0xdc

other info that might help us debug this:
  Chain exists of:
   (work_completion)(&(&guc->timestamp.work)->work) --> fs_reclaim --> 
&gt->reset.mutex
   Possible unsafe locking scenario:
         CPU0                    CPU1
         ----                    ----
    lock(&gt->reset.mutex);
                                 lock(fs_reclaim);
                                 lock(&gt->reset.mutex);
    lock((work_completion)(&(&guc->timestamp.work)->work));

  *** DEADLOCK ***
  3 locks held by kms_pipe_crc_ba/6415:
   #0: ffff888101541430 (sb_writers#15){.+.+}-{0:0}, at: ksys_write+0x64/0xe0
   #1: ffff888136c7eab8 (&attr->mutex){+.+.}-{3:3}, at: 
simple_attr_write_xsigned.constprop.0+0x47/0x110
   #2: ffff88813e6cce90 (&gt->reset.mutex){+.+.}-{3:3}, at: 
intel_gt_reset+0x19e/0x470 [i915]

Signed-off-by: Zhanjun Dong <zhanjun.d...@intel.com>

This unlocks multiple machines on CI, thx.

Reviewed-by: Andrzej Hajda <andrzej.ha...@intel.com>

Regards
Andrzej

---
  drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c 
b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index a0e3ef1c65d2..22390704542e 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -1359,7 +1359,7 @@ static void guc_enable_busyness_worker(struct intel_guc 
*guc)

static void guc_cancel_busyness_worker(struct intel_guc *guc)

  {
-       cancel_delayed_work_sync(&guc->timestamp.work);
+       cancel_delayed_work(&guc->timestamp.work);
  }

static void __reset_guc_busyness_stats(struct intel_guc *guc)