Re: [PATCH] drm/xe: Keep walking on SVM eviction failure

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

On Tue, 2026-09-08 at 12:31 -0700, Matthew Brost wrote:
> On Tue, Sep 08, 2026 at 06:55:22PM +0000,
> sashiko-bot@kernel.org wrote:
> > Thank you for your contribution! Sashiko AI review found 1
> > potential issue(s) to consider:
> > - [Medium] Unconditionally masking `xe_svm_bo_evict()` errors as `-
> > ENOSPC` hides fatal errors and triggers TTM error log spam.
> > --
> > 
> > commit 8fcbc00a7aa0e3b2119f7df96129747882247423
> > Author: Matthew Brost <matthew.brost@intel.com>
> > 
> > drm/xe: Keep walking on SVM eviction failure
> > 
> > This commit adjusts the error handling in xe_bo_move() for SVM
> > eviction
> > failures. It overwrites the return code from xe_svm_bo_evict() with
> > -ENOSPC
> > to force TTM to continue walking the LRU list for eviction
> > candidates.
> > 
> > > diff --git a/drivers/gpu/drm/xe/xe_bo.c
> > > b/drivers/gpu/drm/xe/xe_bo.c
> > > --- a/drivers/gpu/drm/xe/xe_bo.c
> > > +++ b/drivers/gpu/drm/xe/xe_bo.c
> > > @@ -1043,6 +1043,11 @@ static int xe_bo_move(struct
> > > ttm_buffer_object *ttm_bo, bool evict,
> > >  		} else {
> > >  			drm_dbg(&xe->drm, "Evict system
> > > allocator BO failed=%pe\n",
> > >  				ERR_PTR(ret));
> > > +			/*
> > > +			 * The semantic we want upon SVM
> > > eviction failure is
> > > +			 * keep walking for eviction, which is -
> > > ENOSPC.
> > > +			 */
> > > +			ret = -ENOSPC;
> > 
> > [Severity: Medium]
> > Does unconditionally overwriting the error with -ENOSPC hide fatal
> > errors like
> > -ENOMEM?
> > 
> > When system memory is exhausted, xe_svm_bo_evict() can return -
> > ENOMEM. By
> > masking this as -ENOSPC, it seems we might break proper error
> > propagation to
> > higher layers, preventing expected OOM handling.
> > 
> 
> Yea.. Perhaps -ENOMEM should actually be returned to the upper layers
> as
> this indicates we are out of system memory and attemping more
> evictions
> is unlikely to help.
> 
> Second opinion from the Xe team on this one?

IMO we should just convert specific errors (or exclude specific errors)
and add a motivation in the commit message for future reference.

Thanks,
Thomas



> 
> > Furthermore, could this trigger a TTM error log spam loop? When
> > returned to
> > TTM, -ENOSPC causes ttm_bo_evict() to log an unconditional
> > pr_err("Buffer eviction failed\n"). Since -ENOSPC is converted to -
> > EBUSY in
> > ttm_bo_evict_cb(), it signals the LRU walker
> > (ttm_lru_walk_for_evict()) to
> > skip the BO and continue walking. 
> > 
> > During genuine resource exhaustion, this might cause a fruitless
> > iteration over
> > the entire LRU list, logging a pr_err() for every single buffer
> > object. Even
> > benign SVM races might spam the kernel log with errors.
> > 
> 
> The spam is probably seperate issue in TTM. -ENOSPC likely shouldn't
> emit a pr_err as it continues walking.
> 
> Matt
> 
> > >  		}
> > >  
> > >  		goto out;
> > 
> > -- 
> > Sashiko AI review ·
> > https://sashiko.dev/#/patchset/20260908184346.92332-1-matthew.brost@intel.com?part=1