Quoting Tvrtko Ursulin (2020-01-27 15:33:44)
>
> On 26/01/2020 10:23, Chris Wilson wrote:
> > <0> [198.668822] gem_exec-1246 0.... 193899010us : timeline_advance: timeline_advance:387 GEM_BUG_ON(!atomic_read(&tl->pin_count))
> > <0> [198.668859] ---------------------------------
> > <4> [198.669619] ------------[ cut here ]------------
> > <2> [198.669621] kernel BUG at drivers/gpu/drm/i915/gt/intel_timeline.c:387!
> > <4> [198.669703] invalid opcode: 0000 [#1] PREEMPT SMP PTI
> > <4> [198.669712] CPU: 0 PID: 1246 Comm: gem_exec_create Tainted: G U W 5.5.0-rc6-CI-CI_DRM_7755+ #1
> > <4> [198.669723] Hardware name: /NUC7i5BNB, BIOS BNKBL357.86A.0054.2017.1025.1822 10/25/2017
> > <4> [198.669776] RIP: 0010:timeline_advance+0x7b/0xe0 [i915]
> > <4> [198.669785] Code: 00 48 c7 c2 10 f1 46 a0 48 c7 c7 70 1b 32 a0 e8 bb dd e7 e0 bf 01 00 00 00 e8 d1 af e7 e0 31 f6 bf 09 00 00 00 e8 35 ef d8 e0 <0f> 0b 48 c7 c1 48 fa 49 a0 ba 84 01 00 00 48 c7 c6 10 f1 46 a0 48
> > <4> [198.669803] RSP: 0018:ffffc900004c3a38 EFLAGS: 00010296
> > <4> [198.669810] RAX: ffff888270b35140 RBX: ffff88826f32ee00 RCX: 0000000000000006
> > <4> [198.669818] RDX: 00000000000017c5 RSI: 0000000000000000 RDI: 0000000000000009
> > <4> [198.669826] RBP: ffffc900004c3a64 R08: 0000000000000000 R09: 0000000000000000
> > <4> [198.669834] R10: 0000000000000000 R11: 0000000000000000 R12: ffff88826f9b5980
> > <4> [198.669841] R13: 0000000000000cc0 R14: ffffc900004c3dc0 R15: ffff888253610068
> > <4> [198.669849] FS: 00007f63e663fe40(0000) GS:ffff888276c00000(0000) knlGS:0000000000000000
> > <4> [198.669857] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > <4> [198.669864] CR2: 00007f171f8e39a8 CR3: 000000026b1f6005 CR4: 00000000003606f0
> > <4> [198.669872] Call Trace:
> > <4> [198.669924] intel_timeline_get_seqno+0x12/0x40 [i915]
> > <4> [198.669977] __i915_request_create+0x76/0x5a0 [i915]
> > <4> [198.670024] i915_request_create+0x86/0x1c0 [i915]
> > <4> [198.670068] i915_gem_do_execbuffer+0xbf2/0x2500 [i915]
> > <4> [198.670082] ? __lock_acquire+0x460/0x15d0
> > <4> [198.670128] i915_gem_execbuffer2_ioctl+0x11f/0x470 [i915]
> > <4> [198.670171] ? i915_gem_execbuffer_ioctl+0x300/0x300 [i915]
> > <4> [198.670181] drm_ioctl_kernel+0xa7/0xf0
> > <4> [198.670188] drm_ioctl+0x2e1/0x390
> > <4> [198.670233] ? i915_gem_execbuffer_ioctl+0x300/0x300 [i915]
> >
> > Fixes: 841350223816 ("drm/i915/gt: Drop mutex serialisation between context pin/unpin")
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/gt/intel_context.c | 46 ++++++++++++++-----------
> > drivers/gpu/drm/i915/i915_active.h | 6 ++++
> > 2 files changed, 31 insertions(+), 21 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> > index 23137b2a8689..57e8a051ddc2 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_context.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> > @@ -67,21 +67,18 @@ static int intel_context_active_acquire(struct intel_context *ce)
> > {
> > int err;
> >
> > - err = i915_active_acquire(&ce->active);
> > - if (err)
> > - return err;
> > + __i915_active_acquire(&ce->active);
> > +
> > + if (intel_context_is_barrier(ce))
> > + return 0;
> >
> > /* Preallocate tracking nodes */
> > - if (!intel_context_is_barrier(ce)) {
> > - err = i915_active_acquire_preallocate_barrier(&ce->active,
> > - ce->engine);
> > - if (err) {
> > - i915_active_release(&ce->active);
> > - return err;
> > - }
> > - }
> > + err = i915_active_acquire_preallocate_barrier(&ce->active,
> > + ce->engine);
> > + if (err)
> > + i915_active_release(&ce->active);
> >
> > - return 0;
> > + return err;
> > }
> >
> > static void intel_context_active_release(struct intel_context *ce)
> > @@ -101,13 +98,19 @@ int __intel_context_do_pin(struct intel_context *ce)
> > return err;
> > }
> >
> > - if (mutex_lock_interruptible(&ce->pin_mutex))
> > - return -EINTR;
> > + err = i915_active_acquire(&ce->active);
> > + if (err)
> > + return err;
> > +
> > + if (mutex_lock_interruptible(&ce->pin_mutex)) {
> > + err = -EINTR;
> > + goto out_release;
> > + }
> >
> > - if (likely(!atomic_read(&ce->pin_count))) {
> > + if (likely(!atomic_add_unless(&ce->pin_count, 1, 0))) {
> > err = intel_context_active_acquire(ce);
> > if (unlikely(err))
> > - goto err;
> > + goto out_unlock;
> >
> > err = ce->ops->pin(ce);
> > if (unlikely(err))
> > @@ -117,18 +120,19 @@ int __intel_context_do_pin(struct intel_context *ce)
> > ce->ring->head, ce->ring->tail);
> >
> > smp_mb__before_atomic(); /* flush pin before it is visible */
> > + atomic_inc(&ce->pin_count);
> > }
> >
> > - atomic_inc(&ce->pin_count);
> > GEM_BUG_ON(!intel_context_is_pinned(ce)); /* no overflow! */
> > -
> > - mutex_unlock(&ce->pin_mutex);
> > - return 0;
> > + GEM_BUG_ON(i915_active_is_idle(&ce->active));
> > + goto out_unlock;
> >
> > err_active:
> > intel_context_active_release(ce);
> > -err:
> > +out_unlock:
> > mutex_unlock(&ce->pin_mutex);
> > +out_release:
> > + i915_active_release(&ce->active);
> > return err;
> > }
> >
> > diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h
> > index b571f675c795..51e1e854ca55 100644
> > --- a/drivers/gpu/drm/i915/i915_active.h
> > +++ b/drivers/gpu/drm/i915/i915_active.h
> > @@ -188,6 +188,12 @@ int i915_active_acquire(struct i915_active *ref);
> > bool i915_active_acquire_if_busy(struct i915_active *ref);
> > void i915_active_release(struct i915_active *ref);
> >
> > +static inline void __i915_active_acquire(struct i915_active *ref)
> > +{
> > + GEM_BUG_ON(!atomic_read(&ref->count));
> > + atomic_inc(&ref->count);
> > +}
> > +
> > static inline bool
> > i915_active_is_idle(const struct i915_active *ref)
> > {
> >
>
> Change looks okay but I would like to read something more in the commit
> message. Like I feel there is more to it than acquire order otherwise
> problem would be much more widespread.
I added the information about the issue of the mutex_lock vs unlocked
unpin, but the rest of the motion is continuing the theme of trying to
make ww_mutex easier (which you didn't hear).
https://patchwork.freedesktop.org/patch/350849/?series=72626&rev=1
-Chris
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