[Intel-gfx] [PATCH] drm/i915/gt: Add one more rcu_barrier() after draining the ppGTT freelist

[Intel-gfx] [PATCH] drm/i915/gt: Add one more rcu_barrier() after draining the ppGTT freelist

[Chris Wilson]

Since gen7 full-ppgtt uses nested vm references (the ppGTT is a slot
within the global GTT and so has a buried i915_ggtt) we may need to go
through a couple of RCU barriers before we have freed all the structs.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_ggtt.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c b/drivers/gpu/drm/i915/gt/intel_ggtt.c
index 894d08e5a21f..cb31ed712db3 100644
--- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
+++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
@@ -684,8 +684,9 @@ static void ggtt_cleanup_hw(struct i915_ggtt *ggtt)
 
 	atomic_set(&ggtt->vm.open, 0);
 
-	rcu_barrier(); /* flush the RCU'ed__i915_vm_release */
-	flush_workqueue(ggtt->vm.i915->wq);
+	do { /* flush the RCU'ed__i915_vm_release */
+		rcu_barrier();
+	} while (flush_workqueue(ggtt->vm.i915->wq));
 
 	mutex_lock(&ggtt->vm.mutex);
 
-- 
2.20.1

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Re: [Intel-gfx] [PATCH] drm/i915/gt: Add one more rcu_barrier() after draining the ppGTT freelist

[Mika Kuoppala]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Since gen7 full-ppgtt uses nested vm references (the ppGTT is a slot
> within the global GTT and so has a buried i915_ggtt) we may need to go
> through a couple of RCU barriers before we have freed all the structs.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/gt/intel_ggtt.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> index 894d08e5a21f..cb31ed712db3 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> @@ -684,8 +684,9 @@ static void ggtt_cleanup_hw(struct i915_ggtt *ggtt)
>  
>  	atomic_set(&ggtt->vm.open, 0);
>  
> -	rcu_barrier(); /* flush the RCU'ed__i915_vm_release */
> -	flush_workqueue(ggtt->vm.i915->wq);
> +	do { /* flush the RCU'ed__i915_vm_release */
> +		rcu_barrier();
> +	} while (flush_workqueue(ggtt->vm.i915->wq));

flush_workqueue returns void. you want flush_work?
-Mika

>  
>  	mutex_lock(&ggtt->vm.mutex);
>  
> -- 
> 2.20.1
>
> _______________________________________________
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> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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Re: [Intel-gfx] [PATCH] drm/i915/gt: Add one more rcu_barrier() after draining the ppGTT freelist

[Chris Wilson]

Quoting Mika Kuoppala (2020-04-02 09:44:33)
> Chris Wilson <chris@chris-wilson.co.uk> writes:
> 
> > Since gen7 full-ppgtt uses nested vm references (the ppGTT is a slot
> > within the global GTT and so has a buried i915_ggtt) we may need to go
> > through a couple of RCU barriers before we have freed all the structs.
> >
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > ---
> >  drivers/gpu/drm/i915/gt/intel_ggtt.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> > index 894d08e5a21f..cb31ed712db3 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> > @@ -684,8 +684,9 @@ static void ggtt_cleanup_hw(struct i915_ggtt *ggtt)
> >  
> >       atomic_set(&ggtt->vm.open, 0);
> >  
> > -     rcu_barrier(); /* flush the RCU'ed__i915_vm_release */
> > -     flush_workqueue(ggtt->vm.i915->wq);
> > +     do { /* flush the RCU'ed__i915_vm_release */
> > +             rcu_barrier();
> > +     } while (flush_workqueue(ggtt->vm.i915->wq));
> 
> flush_workqueue returns void. you want flush_work?

Darnation. I see in i915_gem_drain_workqueue() we just did N passes :(
-Chris
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Re: [Intel-gfx] [PATCH] drm/i915/gt: Add one more rcu_barrier() after draining the ppGTT freelist

[Chris Wilson]

Quoting Chris Wilson (2020-04-02 09:48:18)
> Quoting Mika Kuoppala (2020-04-02 09:44:33)
> > Chris Wilson <chris@chris-wilson.co.uk> writes:
> > 
> > > Since gen7 full-ppgtt uses nested vm references (the ppGTT is a slot
> > > within the global GTT and so has a buried i915_ggtt) we may need to go
> > > through a couple of RCU barriers before we have freed all the structs.
> > >
> > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > > ---
> > >  drivers/gpu/drm/i915/gt/intel_ggtt.c | 5 +++--
> > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> > > index 894d08e5a21f..cb31ed712db3 100644
> > > --- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
> > > +++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> > > @@ -684,8 +684,9 @@ static void ggtt_cleanup_hw(struct i915_ggtt *ggtt)
> > >  
> > >       atomic_set(&ggtt->vm.open, 0);
> > >  
> > > -     rcu_barrier(); /* flush the RCU'ed__i915_vm_release */
> > > -     flush_workqueue(ggtt->vm.i915->wq);
> > > +     do { /* flush the RCU'ed__i915_vm_release */
> > > +             rcu_barrier();
> > > +     } while (flush_workqueue(ggtt->vm.i915->wq));
> > 
> > flush_workqueue returns void. you want flush_work?
> 
> Darnation. I see in i915_gem_drain_workqueue() we just did N passes :(

Waitasec this is i915->wq, we can just use i915_gem_drain_workqueue()
(although that's now a misnomer).
-Chris
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[Intel-gfx] ✗ Fi.CI.BUILD: failure for drm/i915/gt: Add one more rcu_barrier() after draining the ppGTT freelist

[Patchwork]

== Series Details ==

Series: drm/i915/gt: Add one more rcu_barrier() after draining the ppGTT freelist
URL   : https://patchwork.freedesktop.org/series/75402/
State : failure

== Summary ==

CALL    scripts/checksyscalls.sh
  CALL    scripts/atomic/check-atomics.sh
  DESCEND  objtool
  CHK     include/generated/compile.h
  CC [M]  drivers/gpu/drm/i915/gt/intel_ggtt.o
drivers/gpu/drm/i915/gt/intel_ggtt.c: In function ‘ggtt_cleanup_hw’:
drivers/gpu/drm/i915/gt/intel_ggtt.c:688:11: error: void value not ignored as it ought to be
  } while (flush_workqueue(ggtt->vm.i915->wq));
           ^~~~~~~~~~~~~~~
scripts/Makefile.build:267: recipe for target 'drivers/gpu/drm/i915/gt/intel_ggtt.o' failed
make[4]: *** [drivers/gpu/drm/i915/gt/intel_ggtt.o] Error 1
scripts/Makefile.build:505: recipe for target 'drivers/gpu/drm/i915' failed
make[3]: *** [drivers/gpu/drm/i915] Error 2
scripts/Makefile.build:505: recipe for target 'drivers/gpu/drm' failed
make[2]: *** [drivers/gpu/drm] Error 2
scripts/Makefile.build:505: recipe for target 'drivers/gpu' failed
make[1]: *** [drivers/gpu] Error 2
Makefile:1683: recipe for target 'drivers' failed
make: *** [drivers] Error 2

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Re: [Intel-gfx] [PATCH] drm/i915/gt: Add one more rcu_barrier() after draining the ppGTT freelist

[kbuild test robot]

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Hi Chris,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on drm-intel/for-linux-next]
[also build test ERROR on drm-tip/drm-tip v5.6 next-20200402]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Chris-Wilson/drm-i915-gt-Add-one-more-rcu_barrier-after-draining-the-ppGTT-freelist/20200402-204936
base:   git://anongit.freedesktop.org/drm-intel for-linux-next
config: i386-allyesconfig (attached as .config)
compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   drivers/gpu/drm/i915/gt/intel_ggtt.c: In function 'ggtt_cleanup_hw':
>> drivers/gpu/drm/i915/gt/intel_ggtt.c:671:11: error: void value not ignored as it ought to be
     } while (flush_workqueue(ggtt->vm.i915->wq));
              ^~~~~~~~~~~~~~~

vim +671 drivers/gpu/drm/i915/gt/intel_ggtt.c

   662	
   663	static void ggtt_cleanup_hw(struct i915_ggtt *ggtt)
   664	{
   665		struct i915_vma *vma, *vn;
   666	
   667		atomic_set(&ggtt->vm.open, 0);
   668	
   669		do { /* flush the RCU'ed__i915_vm_release */
   670			rcu_barrier();
 > 671		} while (flush_workqueue(ggtt->vm.i915->wq));
   672	
   673		mutex_lock(&ggtt->vm.mutex);
   674	
   675		list_for_each_entry_safe(vma, vn, &ggtt->vm.bound_list, vm_link)
   676			WARN_ON(__i915_vma_unbind(vma));
   677	
   678		if (drm_mm_node_allocated(&ggtt->error_capture))
   679			drm_mm_remove_node(&ggtt->error_capture);
   680		mutex_destroy(&ggtt->error_mutex);
   681	
   682		ggtt_release_guc_top(ggtt);
   683		intel_vgt_deballoon(ggtt);
   684	
   685		ggtt->vm.cleanup(&ggtt->vm);
   686	
   687		mutex_unlock(&ggtt->vm.mutex);
   688		i915_address_space_fini(&ggtt->vm);
   689	
   690		arch_phys_wc_del(ggtt->mtrr);
   691	
   692		if (ggtt->iomap.size)
   693			io_mapping_fini(&ggtt->iomap);
   694	}
   695	

---
0-DAY CI Kernel Test Service, Intel Corporation
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