[RFC PATCH] dma-buf/dma-fence: Use a successful read_trylock() annotation for dma_fence_begin_signalling()
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 --- 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
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 "Upper layer" here currently being the drm scheduler and "Driver callback" being an xe scheduler callback.
While opt-in annotating the drm scheduler would achieve the same result, I think this patch should be considered anyway, as I don't think we will miss any true lockdep violations as a result of it.
/Thomas
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.
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_);
linaro-mm-sig@lists.linaro.org
-
Thomas Hellström