Hi Zhanjun, On Thu, Jul 27, 2023 at 01:13:23PM -0700, Zhanjun Dong 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. Next time, please wrap the sentences to 65 characters (standing to the e-mail netiquette, RFC1855[1]) or 70-75 characters (standing to the kernel guidelines[2]). [1] https://www.ietf.org/rfc/rfc1855.txt chapter "2.1.1 For mail", page 3 [2] https://docs.kernel.org/process/submitting-patches.html chapter "The canonical patch format" > 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. Thanks for taking care of this, there was a period we could see this splatter everywhere :) > 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); The guc_cancel_busyness_worker() wrapper is made to make life simpler, in oder not to force the caller to find guc->timestamp.work. But if we add a true/false value, then we make it again difficult because we need to go and check what they mean, so that we decrease readability. I would rather prefer something like: static void guc_cancel_busyness_worker_sync(struct intel_guc *guc) { cancel_delayed_work_sync(&guc->timestamp.work); } static void guc_cancel_busyness_worker(struct intel_guc *guc) { cancel_delayed_work(&guc->timestamp.work); } We could perhaps improve this with defines or inlines, but I like this way more. What do you think? Andi > } > > 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); > > 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
