Quoting Chris Wilson (2017-12-13 15:23:31)
> 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>
Michał pointed out that intel_uc_init_wq contains the HAS_GUC, and I
just confused the similar function names.
-Chris
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