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
>
> 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
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
