[Intel-gfx] [PATCH v4] drm/i915: Avoid circular locking dependency when flush delayed work on gt reset

Dong, Zhanjun zhanjun.dong at intel.com
Tue Aug 8 22:03:30 UTC 2023


Hi Andi,


On 2023-08-03 8:36 a.m., Andi Shyti wrote:
> 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"
> 

Thanks, will be fixed in next revision.

>> 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]
>>
>> 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 at intel.com>
>> Cc: John Harrison <John.C.Harrison at Intel.com>
>> Cc: Andi Shyti <andi.shyti at linux.intel.com>
>> ---
>>   .../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

I like this idea, will change it that way in next revision.

Regards,
Zhanjun
> 
>>   }
>>   
>>   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


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