Re: [PATCH 01/15] drm/xe/vm: Don't use a pin the vm_resv during validation

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Wed, 2025-08-13 at 07:28 -0700, Matthew Brost wrote:
> On Wed, Aug 13, 2025 at 12:51:07PM +0200, Thomas Hellström wrote:
> > The pinning has the odd side-effect that unlocking *any* resv
> > during validation triggers an "unlocking pinned lock" warning.
> > 
> 
> So this is a cross process thing then - right? e.g., Process A pins a
> dma-resv lock, Process B unlock a dma-resv lock and boom lockdep
> warning? Just want to make sure I am understandinf the problem
> correctly.

No, my understanding is that this is a single process thing.
We lock the vm, pin it, lock a bo for eviction, perhaps using the same
ww_mutex_ctx, unlock the evicted bo => bang.

It might be that the locks need to be locked using the same ww_mutex
context, but not sure.

/Thomas


> 
> Matt 
> 
> > Cc: Matthew Brost <matthew.brost@intel.com>
> > Fixes: 9d5558649f68 ("drm/xe: Rework eviction rejection of bound
> > external bos")
> > Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > ---
> >  drivers/gpu/drm/xe/xe_bo.c |  5 ++---
> >  drivers/gpu/drm/xe/xe_vm.h | 15 ++-------------
> >  2 files changed, 4 insertions(+), 16 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_bo.c
> > b/drivers/gpu/drm/xe/xe_bo.c
> > index 6fea39842e1e..11eaf3b06766 100644
> > --- a/drivers/gpu/drm/xe/xe_bo.c
> > +++ b/drivers/gpu/drm/xe/xe_bo.c
> > @@ -2468,7 +2468,6 @@ int xe_bo_validate(struct xe_bo *bo, struct
> > xe_vm *vm, bool allow_res_evict)
> >  		.no_wait_gpu = false,
> >  		.gfp_retry_mayfail = true,
> >  	};
> > -	struct pin_cookie cookie;
> >  	int ret;
> >  
> >  	if (vm) {
> > @@ -2479,10 +2478,10 @@ int xe_bo_validate(struct xe_bo *bo, struct
> > xe_vm *vm, bool allow_res_evict)
> >  		ctx.resv = xe_vm_resv(vm);
> >  	}
> >  
> > -	cookie = xe_vm_set_validating(vm, allow_res_evict);
> > +	xe_vm_set_validating(vm, allow_res_evict);
> >  	trace_xe_bo_validate(bo);
> >  	ret = ttm_bo_validate(&bo->ttm, &bo->placement, &ctx);
> > -	xe_vm_clear_validating(vm, allow_res_evict, cookie);
> > +	xe_vm_clear_validating(vm, allow_res_evict);
> >  
> >  	return ret;
> >  }
> > diff --git a/drivers/gpu/drm/xe/xe_vm.h
> > b/drivers/gpu/drm/xe/xe_vm.h
> > index 2f213737c7e5..2ecb417c19a2 100644
> > --- a/drivers/gpu/drm/xe/xe_vm.h
> > +++ b/drivers/gpu/drm/xe/xe_vm.h
> > @@ -315,22 +315,14 @@ void xe_vm_snapshot_free(struct
> > xe_vm_snapshot *snap);
> >   * Register this task as currently making bos resident for the vm.
> > Intended
> >   * to avoid eviction by the same task of shared bos bound to the
> > vm.
> >   * Call with the vm's resv lock held.
> > - *
> > - * Return: A pin cookie that should be used for
> > xe_vm_clear_validating().
> >   */
> > -static inline struct pin_cookie xe_vm_set_validating(struct xe_vm
> > *vm,
> > -						     bool
> > allow_res_evict)
> > +static inline void xe_vm_set_validating(struct xe_vm *vm, bool
> > allow_res_evict)
> >  {
> > -	struct pin_cookie cookie = {};
> > -
> >  	if (vm && !allow_res_evict) {
> >  		xe_vm_assert_held(vm);
> > -		cookie = lockdep_pin_lock(&xe_vm_resv(vm)-
> > >lock.base);
> >  		/* Pairs with READ_ONCE in xe_vm_is_validating()
> > */
> >  		WRITE_ONCE(vm->validating, current);
> >  	}
> > -
> > -	return cookie;
> >  }
> >  
> >  /**
> > @@ -338,17 +330,14 @@ static inline struct pin_cookie
> > xe_vm_set_validating(struct xe_vm *vm,
> >   * @vm: Pointer to the vm or NULL
> >   * @allow_res_evict: Eviction from @vm was allowed. Must be set to
> > the same
> >   * value as for xe_vm_set_validation().
> > - * @cookie: Cookie obtained from xe_vm_set_validating().
> >   *
> >   * Register this task as currently making bos resident for the vm.
> > Intended
> >   * to avoid eviction by the same task of shared bos bound to the
> > vm.
> >   * Call with the vm's resv lock held.
> >   */
> > -static inline void xe_vm_clear_validating(struct xe_vm *vm, bool
> > allow_res_evict,
> > -					  struct pin_cookie
> > cookie)
> > +static inline void xe_vm_clear_validating(struct xe_vm *vm, bool
> > allow_res_evict)
> >  {
> >  	if (vm && !allow_res_evict) {
> > -		lockdep_unpin_lock(&xe_vm_resv(vm)->lock.base,
> > cookie);
> >  		/* Pairs with READ_ONCE in xe_vm_is_validating()
> > */
> >  		WRITE_ONCE(vm->validating, NULL);
> >  	}
> > -- 
> > 2.50.1
> >