[Intel-gfx] [PATCH] drm/i915/gtt: Always acquire struct_mutex for gen6_ppgtt_cleanup

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-05-23 11:01:09)
> 
> On 23/05/2019 10:21, Tvrtko Ursulin wrote:
> > 
> > On 23/05/2019 07:49, Chris Wilson wrote:
> >> We rearranged the vm_destroy_ioctl to avoid taking struct_mutex, little
> >> realising that buried underneath the gen6 ppgtt release path was a
> >> struct_mutex requirement (to remove its GGTT vma). Until that
> >> struct_mutex is vanquished, take a detour in gen6_ppgtt_cleanup to do
> >> the i915_vma_destroy from inside a worker under the struct_mutex.
> >>
> >> <4> [257.740160] WARN_ON(debug_locks && 
> >> !lock_is_held(&(&vma->vm->i915->drm.struct_mutex)->dep_map))
> >> <4> [257.740213] WARNING: CPU: 3 PID: 1507 at 
> >> drivers/gpu/drm/i915/i915_vma.c:841 i915_vma_destroy+0x1ae/0x3a0 [i915]
> >> <4> [257.740214] Modules linked in: snd_hda_codec_hdmi i915 
> >> x86_pkg_temp_thermal mei_hdcp coretemp crct10dif_pclmul crc32_pclmul 
> >> ghash_clmulni_intel snd_hda_codec_realtek snd_hda_codec_generic 
> >> snd_hda_intel snd_hda_codec snd_hwdep snd_hda_core r8169 realtek 
> >> snd_pcm mei_me mei prime_numbers lpc_ich
> >> <4> [257.740224] CPU: 3 PID: 1507 Comm: gem_vm_create Tainted: G     
> >> U            5.2.0-rc1-CI-CI_DRM_6118+ #1
> >> <4> [257.740225] Hardware name: MSI MS-7924/Z97M-G43(MS-7924), BIOS 
> >> V1.12 02/15/2016
> >> <4> [257.740249] RIP: 0010:i915_vma_destroy+0x1ae/0x3a0 [i915]
> >> <4> [257.740250] Code: 00 00 00 48 81 c7 c8 00 00 00 e8 ed 08 f0 e0 85 
> >> c0 0f 85 78 fe ff ff 48 c7 c6 e8 ec 30 a0 48 c7 c7 da 55 33 a0 e8 42 
> >> 8c e9 e0 <0f> 0b 8b 83 40 01 00 00 85 c0 0f 84 63 fe ff ff 48 c7 c1 c1 
> >> 58 33
> >> <4> [257.740251] RSP: 0018:ffffc90000aafc68 EFLAGS: 00010282
> >> <4> [257.740252] RAX: 0000000000000000 RBX: ffff8883f7957840 RCX: 
> >> 0000000000000003
> >> <4> [257.740253] RDX: 0000000000000046 RSI: 0000000000000006 RDI: 
> >> ffffffff8212d1b9
> >> <4> [257.740254] RBP: ffffc90000aafcc8 R08: 0000000000000000 R09: 
> >> 0000000000000000
> >> <4> [257.740255] R10: 0000000000000000 R11: 0000000000000000 R12: 
> >> ffff8883f4d5c2a8
> >> <4> [257.740256] R13: ffff8883f4d5d680 R14: ffff8883f4d5c668 R15: 
> >> ffff8883f4d5c2f0
> >> <4> [257.740257] FS:  00007f777fa8fe40(0000) GS:ffff88840f780000(0000) 
> >> knlGS:0000000000000000
> >> <4> [257.740258] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> <4> [257.740259] CR2: 00007f777f6522b0 CR3: 00000003c612a006 CR4: 
> >> 00000000001606e0
> >> <4> [257.740260] Call Trace:
> >> <4> [257.740283]  gen6_ppgtt_cleanup+0x25/0x60 [i915]
> >> <4> [257.740306]  i915_ppgtt_release+0x102/0x290 [i915]
> >> <4> [257.740330]  i915_gem_vm_destroy_ioctl+0x7c/0xa0 [i915]
> >> <4> [257.740376]  ? i915_gem_vm_create_ioctl+0x160/0x160 [i915]
> >> <4> [257.740379]  drm_ioctl_kernel+0x83/0xf0
> >> <4> [257.740382]  drm_ioctl+0x2f3/0x3b0
> >> <4> [257.740422]  ? i915_gem_vm_create_ioctl+0x160/0x160 [i915]
> >> <4> [257.740426]  ? _raw_spin_unlock_irqrestore+0x39/0x60
> >> <4> [257.740430]  do_vfs_ioctl+0xa0/0x6e0
> >> <4> [257.740433]  ? lock_acquire+0xa6/0x1c0
> >> <4> [257.740436]  ? __task_pid_nr_ns+0xb9/0x1f0
> >> <4> [257.740439]  ksys_ioctl+0x35/0x60
> >> <4> [257.740441]  __x64_sys_ioctl+0x11/0x20
> >> <4> [257.740443]  do_syscall_64+0x55/0x1c0
> >> <4> [257.740445]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >>
> >> References: e0695db7298e ("drm/i915: Create/destroy VM (ppGTT) for use 
> >> with contexts")
> >> Fixes: 7f3f317a66ca ("drm/i915: Restore control over ppgtt for context 
> >> creation ABI")
> >> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> >> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >> ---
> >>   drivers/gpu/drm/i915/i915_gem_gtt.c | 32 +++++++++++++++++++++++++++--
> >>   drivers/gpu/drm/i915/i915_gem_gtt.h |  2 ++
> >>   2 files changed, 32 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c 
> >> b/drivers/gpu/drm/i915/i915_gem_gtt.c
> >> index 9ed41aefb456..5a350251766a 100644
> >> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> >> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> >> @@ -1828,11 +1828,33 @@ static void gen6_ppgtt_free_pd(struct 
> >> gen6_hw_ppgtt *ppgtt)
> >>               free_pt(&ppgtt->base.vm, pt);
> >>   }
> >> +struct gen6_ppgtt_cleanup_work {
> >> +    struct work_struct base;
> >> +    struct i915_vma *vma;
> >> +};
> >> +
> >> +static void gen6_ppgtt_cleanup_work(struct work_struct *wrk)
> >> +{
> >> +    struct gen6_ppgtt_cleanup_work *work =
> >> +        container_of(wrk, typeof(*work), base);
> >> +    struct drm_i915_private *i915 = work->vma->vm->i915;
> > 
> > Does the sequence need an extra reference on ppgtt for dereferencing the 
> > vm here? Alternatively storing i915 in the work struct could work around 
> > that.
> 
> Nope - vma has a pointer to vm as well which it will dereference. So if 
> reference is needed it's needed - it looks like it is to me, since only 
> contexts take them, which vma's still rely on, right?

Nah, vm is decidedly dead at this point, we just need to stuff the i915
pointer into the cleanup_work.
-Chris