[PATCH 1/2] dma-buf: add dma_fence_unwrap

[Daniel Vetter]

On Mon, Mar 28, 2022 at 04:26:44PM +0200, Christian König wrote:
> Am 28.03.22 um 16:22 schrieb Daniel Vetter:
> > On Mon, Mar 28, 2022 at 12:28:31PM +0200, Christian König wrote:
> > > Hi Ville & Daniel,
> > > 
> > > Am 25.03.22 um 16:28 schrieb Christian König:
> > > > Am 25.03.22 um 16:25 schrieb Ville Syrjälä:
> > > > > On Fri, Mar 11, 2022 at 12:02:43PM +0100, Christian König wrote:
> > > > > > Add a general purpose helper to deep dive into
> > > > > > dma_fence_chain/dma_fence_array
> > > > > > structures and iterate over all the fences in them.
> > > > > > 
> > > > > > This is useful when we need to flatten out all fences in those
> > > > > > structures.
> > > > > > 
> > > > > > Signed-off-by: Christian König <christian.koenig at amd.com>
> > > > > One of the dma-buf patches took down Intel CI. Looks like every
> > > > > machine oopses in some sync_file thing now:
> > > > > <1>[  260.470008] BUG: kernel NULL pointer dereference, address:
> > > > > 0000000000000010
> > > > > <1>[  260.470020] #PF: supervisor read access in kernel mode
> > > > > <1>[  260.470025] #PF: error_code(0x0000) - not-present page
> > > > > <6>[  260.470030] PGD 0 P4D 0
> > > > > <4>[  260.470035] Oops: 0000 [#1] PREEMPT SMP NOPTI
> > > > > <4>[  260.470040] CPU: 0 PID: 5306 Comm: core_hotunplug Not tainted
> > > > > 5.17.0-CI-CI_DRM_11405+ #1
> > > > > <4>[  260.470049] Hardware name: Intel Corporation Jasper Lake
> > > > > Client Platform/Jasperlake DDR4 SODIMM RVP, BIOS
> > > > > JSLSFWI1.R00.2385.D02.2010160831 10/16/2020
> > > > > <4>[  260.470058] RIP: 0010:dma_fence_array_first+0x19/0x20
> > > I've looked into this and the root cause seems to be that the new code
> > > doesn't handle dma_fence_arrays with zero elements.
> > > 
> > > That is rather easy to fix, but a dma_fence_array with zero number of
> > > elements is most likely a bug because under the wrong circumstances it can
> > > create a dma_fence instance which will never signal.
> > > 
> > > I've send out a patch on Frinday ([PATCH] dma-buf: WIP dma_fence_array_first
> > > fix) which avoids the crash and prints a warning if anybody tries to create
> > > a dma_fence_array with zero length.
> > > 
> > > Can you test this?
> > It's in drm-tip now (in the fixup branch) so drm-tip results should have
> > the result soonish:
> > 
> > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fintel-gfx-ci.01.org%2Ftree%2Fdrm-tip%2Findex.html&data=04%7C01%7Cchristian.koenig%40amd.com%7C0afc74b5df0c4ea384af08da10c672fa%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637840742273792356%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=SL2CuMgM6lCSOhDTvs%2FaFg6zRlc7F3X%2BNkf6GuGMGXI%3D&reserved=0?
> 
> How do I find something in there? Is there a search function over all the
> test results?

Not really. You can ask on #intel-gfx-ci, or look at the tests that have
blown up without this to know where to look.

You can also download all the logfiles with wget recursive or so from the
build directory (the links in the top row) and search locally.
-Daniel

> 
> Thanks,
> Christian.
> 
> > 
> > Cheers, Daniel
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch