Quoting Michał Winiarski (2017-12-13 12:50:40)
> This gets rid of the following lockdep splat:
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 4.15.0-rc2-CI-Patchwork_7428+ #1 Not tainted
> ------------------------------------------------------
> debugfs_test/1351 is trying to acquire lock:
> (&dev->struct_mutex){+.+.}, at: [<000000009d90d1a3>] i915_mutex_lock_interruptible+0x47/0x130 [i915]
>
> but task is already holding lock:
> (&mm->mmap_sem){++++}, at: [<000000005df01c1e>] __do_page_fault+0x106/0x560
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #6 (&mm->mmap_sem){++++}:
> __might_fault+0x63/0x90
> _copy_to_user+0x1e/0x70
> filldir+0x8c/0xf0
> dcache_readdir+0xeb/0x160
> iterate_dir+0xe6/0x150
> SyS_getdents+0xa0/0x130
> entry_SYSCALL_64_fastpath+0x1c/0x89
>
> -> #5 (&sb->s_type->i_mutex_key#5){++++}:
> lockref_get+0x9/0x20
>
> -> #4 ((completion)&req.done){+.+.}:
> wait_for_common+0x54/0x210
> devtmpfs_create_node+0x130/0x150
> device_add+0x5ad/0x5e0
> device_create_groups_vargs+0xd4/0xe0
> device_create+0x35/0x40
> msr_device_create+0x22/0x40
> cpuhp_invoke_callback+0xc5/0xbf0
> cpuhp_thread_fun+0x167/0x210
> smpboot_thread_fn+0x17f/0x270
> kthread+0x173/0x1b0
> ret_from_fork+0x24/0x30
>
> -> #3 (cpuhp_state-up){+.+.}:
> cpuhp_issue_call+0x132/0x1c0
> __cpuhp_setup_state_cpuslocked+0x12f/0x2a0
> __cpuhp_setup_state+0x3a/0x50
> page_writeback_init+0x3a/0x5c
> start_kernel+0x393/0x3e2
> secondary_startup_64+0xa5/0xb0
>
> -> #2 (cpuhp_state_mutex){+.+.}:
> __mutex_lock+0x81/0x9b0
> __cpuhp_setup_state_cpuslocked+0x4b/0x2a0
> __cpuhp_setup_state+0x3a/0x50
> page_alloc_init+0x1f/0x26
> start_kernel+0x139/0x3e2
> secondary_startup_64+0xa5/0xb0
>
> -> #1 (cpu_hotplug_lock.rw_sem){++++}:
> cpus_read_lock+0x34/0xa0
> apply_workqueue_attrs+0xd/0x40
> __alloc_workqueue_key+0x2c7/0x4e1
> intel_guc_submission_init+0x10c/0x650 [i915]
> intel_uc_init_hw+0x29e/0x460 [i915]
> i915_gem_init_hw+0xca/0x290 [i915]
> i915_gem_init+0x115/0x3a0 [i915]
> i915_driver_load+0x9a8/0x16c0 [i915]
> i915_pci_probe+0x2e/0x90 [i915]
> pci_device_probe+0x9c/0x120
> driver_probe_device+0x2a3/0x480
> __driver_attach+0xd9/0xe0
> bus_for_each_dev+0x57/0x90
> bus_add_driver+0x168/0x260
> driver_register+0x52/0xc0
> do_one_initcall+0x39/0x150
> do_init_module+0x56/0x1ef
> load_module+0x231c/0x2d70
> SyS_finit_module+0xa5/0xe0
> entry_SYSCALL_64_fastpath+0x1c/0x89
>
> -> #0 (&dev->struct_mutex){+.+.}:
> lock_acquire+0xaf/0x200
> __mutex_lock+0x81/0x9b0
> i915_mutex_lock_interruptible+0x47/0x130 [i915]
> i915_gem_fault+0x201/0x760 [i915]
> __do_fault+0x15/0x70
> __handle_mm_fault+0x85b/0xe40
> handle_mm_fault+0x14f/0x2f0
> __do_page_fault+0x2d1/0x560
> page_fault+0x22/0x30
>
> other info that might help us debug this:
>
> Chain exists of:
> &dev->struct_mutex --> &sb->s_type->i_mutex_key#5 --> &mm->mmap_sem
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&mm->mmap_sem);
> lock(&sb->s_type->i_mutex_key#5);
> lock(&mm->mmap_sem);
> lock(&dev->struct_mutex);
>
> *** DEADLOCK ***
>
> 1 lock held by debugfs_test/1351:
> #0: (&mm->mmap_sem){++++}, at: [<000000005df01c1e>] __do_page_fault+0x106/0x560
>
> stack backtrace:
> CPU: 2 PID: 1351 Comm: debugfs_test Not tainted 4.15.0-rc2-CI-Patchwork_7428+ #1
> Hardware name: /NUC6i5SYB, BIOS SYSKLi35.86A.0057.2017.0119.1758 01/19/2017
> Call Trace:
> dump_stack+0x5f/0x86
> print_circular_bug+0x230/0x3b0
> check_prev_add+0x439/0x7b0
> ? lockdep_init_map_crosslock+0x20/0x20
> ? unwind_get_return_address+0x16/0x30
> ? __lock_acquire+0x1385/0x15a0
> __lock_acquire+0x1385/0x15a0
> lock_acquire+0xaf/0x200
> ? i915_mutex_lock_interruptible+0x47/0x130 [i915]
> __mutex_lock+0x81/0x9b0
> ? i915_mutex_lock_interruptible+0x47/0x130 [i915]
> ? i915_mutex_lock_interruptible+0x47/0x130 [i915]
> ? i915_mutex_lock_interruptible+0x47/0x130 [i915]
> i915_mutex_lock_interruptible+0x47/0x130 [i915]
> ? __pm_runtime_resume+0x4f/0x80
> i915_gem_fault+0x201/0x760 [i915]
> __do_fault+0x15/0x70
> __handle_mm_fault+0x85b/0xe40
> handle_mm_fault+0x14f/0x2f0
> __do_page_fault+0x2d1/0x560
> page_fault+0x22/0x30
> RIP: 0033:0x7f98d6f49116
> RSP: 002b:00007ffd6ffc3278 EFLAGS: 00010283
> RAX: 00007f98d39a2bc0 RBX: 0000000000000000 RCX: 0000000000001680
> RDX: 0000000000001680 RSI: 00007ffd6ffc3400 RDI: 00007f98d39a2bc0
> RBP: 00007ffd6ffc33a0 R08: 0000000000000000 R09: 00000000000005a0
> R10: 000055e847c2a830 R11: 0000000000000002 R12: 0000000000000001
> R13: 000055e847c1d040 R14: 00007ffd6ffc3400 R15: 00007f98d6752ba0
>
> v2: Init preempt_work unconditionally (Chris)
>
> Testcase: igt/debugfs_test/read_all_entries
With a #i915.enable_guc=1 addendum (or something)
> Signed-off-by: Michał Winiarski <michal.winiarski@xxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: Michal Wajdeczko <michal.wajdeczko@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_drv.c | 1 +
> drivers/gpu/drm/i915/i915_gem.c | 4 ++
> drivers/gpu/drm/i915/intel_guc.c | 57 +++++++++++++++++++++++
> drivers/gpu/drm/i915/intel_guc.h | 2 +
> drivers/gpu/drm/i915/intel_guc_log.c | 23 ----------
> drivers/gpu/drm/i915/intel_guc_submission.c | 70 +++++++----------------------
> drivers/gpu/drm/i915/intel_guc_submission.h | 2 +
> drivers/gpu/drm/i915/intel_uc.c | 26 +++++++++++
> drivers/gpu/drm/i915/intel_uc.h | 2 +
> 9 files changed, 110 insertions(+), 77 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 721ccce1832f..285c8b238bff 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -621,6 +621,7 @@ static void i915_gem_fini(struct drm_i915_private *dev_priv)
> i915_gem_contexts_fini(dev_priv);
> mutex_unlock(&dev_priv->drm.struct_mutex);
>
> + intel_uc_fini_wq(dev_priv);
> i915_gem_cleanup_userptr(dev_priv);
>
> i915_gem_drain_freed_objects(dev_priv);
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 8c3d801696b7..4b2ca43a610f 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -5160,6 +5160,10 @@ int i915_gem_init(struct drm_i915_private *dev_priv)
> if (ret)
> return ret;
>
> + ret = intel_uc_init_wq(dev_priv);
> + if (ret)
> + return ret;
> +
> /* This is just a security blanket to placate dragons.
> * On some systems, we very sporadically observe that the first TLBs
> * used by the CS may be stale, despite us poking the TLB reset. If
> diff --git a/drivers/gpu/drm/i915/intel_guc.c b/drivers/gpu/drm/i915/intel_guc.c
> index 92ed22f38fc4..3c6bf5a34c3c 100644
> --- a/drivers/gpu/drm/i915/intel_guc.c
> +++ b/drivers/gpu/drm/i915/intel_guc.c
> @@ -69,6 +69,63 @@ void intel_guc_init_early(struct intel_guc *guc)
> guc->notify = gen8_guc_raise_irq;
> }
>
> +int intel_guc_init_wq(struct intel_guc *guc)
> +{
> + struct drm_i915_private *dev_priv = guc_to_i915(guc);
if (!HAS_GUC()) or if (!USES_GUC()) ?
I think you want at least the former.
But other than the extra allocation,
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
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