On Fri, 2021-05-28 at 09:16 +0200, Christian König wrote:
Am 27.05.21 um 17:51 schrieb Thomas Hellström:
On Thu, 2021-05-27 at 17:32 +0200, Christian König wrote:
Am 27.05.21 um 17:05 schrieb Thomas Hellström:
On Thu, 2021-05-27 at 17:01 +0200, Thomas Hellström wrote:
On Thu, 2021-05-27 at 16:54 +0200, Christian König wrote:
Am 27.05.21 um 16:19 schrieb Thomas Hellström: > The swapping code was dereference bo->ttm pointers > without > having > the > dma-resv lock held. Also it might try to swap out > unpopulated > bos. > > Fix this by moving the bo->ttm dereference until we have > the > reservation > lock. Check that the ttm_tt is populated after the > swap_notify > callback. > > Signed-off-by: Thomas Hellström > thomas.hellstrom@linux.intel.com > --- > drivers/gpu/drm/ttm/ttm_bo.c | 16 > +++++++++++++++- > drivers/gpu/drm/ttm/ttm_device.c | 8 +++----- > 2 files changed, 18 insertions(+), 6 deletions(-) > > diff --git a/drivers/gpu/drm/ttm/ttm_bo.c > b/drivers/gpu/drm/ttm/ttm_bo.c > index 9f53506a82fc..86213d37657b 100644 > --- a/drivers/gpu/drm/ttm/ttm_bo.c > +++ b/drivers/gpu/drm/ttm/ttm_bo.c > @@ -1163,6 +1163,16 @@ int ttm_bo_swapout(struct > ttm_buffer_object > *bo, struct ttm_operation_ctx *ctx, > if (!ttm_bo_evict_swapout_allowable(bo, ctx, > &place, > &locked, NULL)) > return -EBUSY; > > + dma_resv_assert_held(bo->base.resv); > + > + if (!bo->ttm || > + bo->ttm->page_flags & TTM_PAGE_FLAG_SG || > + bo->ttm->page_flags & TTM_PAGE_FLAG_SWAPPED) > { > + if (locked) > + dma_resv_unlock(bo->base.resv); > + return -EBUSY; > + } > + > if (!ttm_bo_get_unless_zero(bo)) { > if (locked) > dma_resv_unlock(bo->base.resv); > @@ -1215,7 +1225,8 @@ int ttm_bo_swapout(struct > ttm_buffer_object > *bo, struct ttm_operation_ctx *ctx, > if (bo->bdev->funcs->swap_notify) > bo->bdev->funcs->swap_notify(bo); > > - ret = ttm_tt_swapout(bo->bdev, bo->ttm, > gfp_flags); > + if (ttm_tt_is_populated(bo->ttm)) > + ret = ttm_tt_swapout(bo->bdev, bo->ttm, > gfp_flags); Exactly that is what I won't recommend. We would try to swap out the same BO over and over again with that.
But we wouldn't since the BO is taken off the LRU and never re- added,
In fact, we'd probably might want to take the !bo->ttm bos off the LRU as well..
No, we don't want to take any BOs of the LRU unless they are pinned.
Adding a TT object or populating it doesn't necessarily put the BO back to the LRU.
OK, but swapped bos are also taken off the LRU list so these unpopulated bos are just taking the same path. Only difference to swapped is that they don't get read back on re-populate, but typically cleared.
But what would be the point of keeping swapped-out bos on the LRU list?, particularly when we're iterating under a spinlock? Shouldn't we try to re-add to LRU (if not already on an LRU) just before populating? There aren't really that many calls in core TTM.
I want to avoid removing BOs from the LRU as much as possible since we forgot on multiple places that we want to re-add them.
Conceptual I think the swapped BOs should have a separate memory domain, this way we can ignore them cleanly when swapping things out.
Yes, that would of course work as well. Keeping them on the system LRU is IMO highly undesirable.
Going to pick this patch up, modifying it a bit more and then pushing it to drm-misc-fixes for upstreaming.
OK, I dropped the TTM fix for the purge-in-swap-notify from the i915 series, hoping that the reworked variant of this patch lands first.
Thanks, Thomas
Thanks, Christian.
/Thomas
Christian.
/Thomas