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Are you seeing any allocations happening during unmap? I don't >> immediately see any, but that sounds surprising. > > Not allocations but we are acquiring locks during unmap. My understanding > is (at least some) unmaps have to also be done in the dma fence signaling > critical path (the run stage), but Danilo/you can correct me if I am wrong > on that. We cannot avoid all locking but those same locks cannot be held in > any other paths which do a memory allocation (as mentioned in one of the > deadlock scenarios), that is probably the main thing to check for unmap. > Right, OK we are on the same page now: no allocations happening on unmap, but it can still deadlock, because the driver is typically going to use a single lock to protect calls both map and unmap-related calls to the buddy allocator. For the deadlock above, I think a good way to break that deadlock is to not allow taking that lock in a fence signaling calling path. So during an unmap, instead of "lock, unmap/free, unlock" it should move the item to a deferred-free list, which is processed separately. Of course, this is a little complex, because the allocation and reclaim has to be aware of such lists if they get large. thanks, -- John Hubbard