Hi Daniel, On 2023-08-03 9:03 a.m., Daniel Vetter wrote:
On Thu, 27 Jul 2023 at 22:13, Zhanjun Dong <zhanjun.dong@xxxxxxxxx> wrote:This attempts to avoid circular locking dependency between flush delayed work and intel_gt_reset. Switched from cancel_delayed_work_sync to cancel_delayed_work, the non-sync version for reset path, it is safe as the worker has the trylock code to handle the lock; Meanwhile keep the sync version for park/fini to ensure the worker is not still running during suspend or shutdown. 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 (>->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 (>->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 (>->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 --> >->reset.mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(>->reset.mutex); lock(fs_reclaim); lock(>->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 (>->reset.mutex){+.+.}-{3:3}, at: intel_gt_reset+0x19e/0x470 [i915] v2: Add sync flag to guc_cancel_busyness_worker to ensure reset path calls asynchronous cancel. v3: Add sync flag to intel_guc_submission_disable to ensure reset path calls asynchronous cancel. v4: Set to always sync from __uc_fini_hw path. Signed-off-by: Zhanjun Dong <zhanjun.dong@xxxxxxxxx> Cc: John Harrison <John.C.Harrison@xxxxxxxxx> Cc: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx> --- .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 17 ++++++++++------- .../gpu/drm/i915/gt/uc/intel_guc_submission.h | 2 +- drivers/gpu/drm/i915/gt/uc/intel_uc.c | 4 ++-- 3 files changed, 13 insertions(+), 10 deletions(-) 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..ef4300246ce1 100644 --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c @@ -1357,9 +1357,12 @@ static void guc_enable_busyness_worker(struct intel_guc *guc) mod_delayed_work(system_highpri_wq, &guc->timestamp.work, guc->timestamp.ping_delay); } -static void guc_cancel_busyness_worker(struct intel_guc *guc) +static void guc_cancel_busyness_worker(struct intel_guc *guc, bool sync) { - cancel_delayed_work_sync(&guc->timestamp.work); + if (sync) + cancel_delayed_work_sync(&guc->timestamp.work); + else + cancel_delayed_work(&guc->timestamp.work); } static void __reset_guc_busyness_stats(struct intel_guc *guc) @@ -1370,7 +1373,7 @@ static void __reset_guc_busyness_stats(struct intel_guc *guc) unsigned long flags; ktime_t unused; - guc_cancel_busyness_worker(guc); + guc_cancel_busyness_worker(guc, false);This needs an absolutely giantic explainer of why this is correct, and why it's needed. I suspect this one of these "shut up lockdep, break the code" kind of patches. -Daniel
Thanks for comments. Will add more code comments in next revision. Regards, Zhanjun
spin_lock_irqsave(&guc->timestamp.lock, flags); @@ -1485,7 +1488,7 @@ static int guc_init_engine_stats(struct intel_guc *guc) static void guc_fini_engine_stats(struct intel_guc *guc) { - guc_cancel_busyness_worker(guc); + guc_cancel_busyness_worker(guc, true); } void intel_guc_busyness_park(struct intel_gt *gt) @@ -1500,7 +1503,7 @@ void intel_guc_busyness_park(struct intel_gt *gt) * and causes an unclaimed register access warning. Cancel the worker * synchronously here. */ - guc_cancel_busyness_worker(guc); + guc_cancel_busyness_worker(guc, true); /* * Before parking, we should sample engine busyness stats if we need to. @@ -4501,9 +4504,9 @@ int intel_guc_submission_enable(struct intel_guc *guc) } /* Note: By the time we're here, GuC may have already been reset */ -void intel_guc_submission_disable(struct intel_guc *guc) +void intel_guc_submission_disable(struct intel_guc *guc, bool sync) { - guc_cancel_busyness_worker(guc); + guc_cancel_busyness_worker(guc, sync); /* Semaphore interrupt disable and route to host */ guc_route_semaphores(guc, false); diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.h b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.h index c57b29cdb1a6..a77de0d6ed58 100644 --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.h +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.h @@ -16,7 +16,7 @@ struct intel_engine_cs; void intel_guc_submission_init_early(struct intel_guc *guc); int intel_guc_submission_init(struct intel_guc *guc); int intel_guc_submission_enable(struct intel_guc *guc); -void intel_guc_submission_disable(struct intel_guc *guc); +void intel_guc_submission_disable(struct intel_guc *guc, bool sync); void intel_guc_submission_fini(struct intel_guc *guc); int intel_guc_preempt_work_create(struct intel_guc *guc); void intel_guc_preempt_work_destroy(struct intel_guc *guc); diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc.c b/drivers/gpu/drm/i915/gt/uc/intel_uc.c index 18250fb64bd8..5b76f0d4d2a6 100644 --- a/drivers/gpu/drm/i915/gt/uc/intel_uc.c +++ b/drivers/gpu/drm/i915/gt/uc/intel_uc.c @@ -566,7 +566,7 @@ static int __uc_init_hw(struct intel_uc *uc) * We've failed to load the firmware :( */ err_submission: - intel_guc_submission_disable(guc); + intel_guc_submission_disable(guc, true); err_log_capture: __uc_capture_load_err_log(uc); err_rps: @@ -597,7 +597,7 @@ static void __uc_fini_hw(struct intel_uc *uc) return; if (intel_uc_uses_guc_submission(uc)) - intel_guc_submission_disable(guc); + intel_guc_submission_disable(guc, true); __uc_sanitize(uc); } -- 2.34.1
