Christian,
Ping?
On Wed, 2024-08-14 at 10:37 +0200, Thomas Hellström wrote:
Christian,
Ack to merge this through drm-misc-next, or do you want to pick it up for dma-buf?
Thanks, Thomas
On Wed, 2024-08-14 at 09:10 +0200, Daniel Vetter wrote:
On Fri, May 26, 2023 at 01:11:28PM +0200, Thomas Hellström wrote:
Daniel,
On 4/28/23 14:52, Thomas Hellström wrote:
Condsider the following call sequence:
/* Upper layer */ dma_fence_begin_signalling(); lock(tainted_shared_lock); /* Driver callback */ dma_fence_begin_signalling(); ...
The driver might here use a utility that is annotated as intended for the dma-fence signalling critical path. Now if the upper layer isn't correctly annotated yet for whatever reason, resulting in
/* Upper layer */ lock(tainted_shared_lock); /* Driver callback */ dma_fence_begin_signalling();
We will receive a false lockdep locking order violation notification from dma_fence_begin_signalling(). However entering a dma-fence signalling critical section itself doesn't block and could not cause a deadlock.
So use a successful read_trylock() annotation instead for dma_fence_begin_signalling(). That will make sure that the locking order is correctly registered in the first case, and doesn't register any locking order in the second case.
The alternative is of course to make sure that the "Upper layer" is always correctly annotated. But experience shows that's not easily achievable in all cases.
Signed-off-by: Thomas Hellström thomas.hellstrom@linux.intel.com
Resurrecting the discussion on this one. I can't see a situation where we would miss *relevant* locking order violation warnings with this patch. Ofc if we have a scheduler annotation patch that would work fine as well, but the lack of annotation in the scheduler callbacks is really starting to hurt us.
Yeah this is just a bit too brain-melting to review, but I concur now.
Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch
I think what would help is some lockdep selftests to check that we both catch the stuff we want to, and don't incur false positives. Maybe with a plea that lockdep should have some native form of cross-release annotations ...
But definitely seperate patch set, since it might take a few rounds of review by lockdep folks. -Sima
Thanks,
Thomas
drivers/dma-buf/dma-fence.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma- fence.c index f177c56269bb..17f632768ef9 100644 --- a/drivers/dma-buf/dma-fence.c +++ b/drivers/dma-buf/dma-fence.c @@ -308,8 +308,8 @@ bool dma_fence_begin_signalling(void) if (in_atomic()) return true;
- /* ... and non-recursive readlock */
- lock_acquire(&dma_fence_lockdep_map, 0, 0, 1, 1, NULL,
_RET_IP_);
- /* ... and non-recursive successful read_trylock */
- lock_acquire(&dma_fence_lockdep_map, 0, 1, 1, 1, NULL,
_RET_IP_); return false; } @@ -340,7 +340,7 @@ void __dma_fence_might_wait(void) lock_map_acquire(&dma_fence_lockdep_map); lock_map_release(&dma_fence_lockdep_map); if (tmp)
lock_acquire(&dma_fence_lockdep_map, 0, 0, 1,1, NULL, _THIS_IP_);
lock_acquire(&dma_fence_lockdep_map, 0, 1, 1,1, NULL, _THIS_IP_); } #endif