In the Linux kernel, the following vulnerability has been resolved:dma-debug: fix a possible deadlock on radix_lockradix_lock() shouldn't be held while holding dma_hash_entry[idx].lock
otherwise, there's a possible deadlock scenario when
dma debug API is called holding rq_lock():CPU0                   CPU1                       CPU2
dma_free_attrs()
check_unmap()          add_dma_entry()            __schedule() //out
                                                  (A) rq_lock()
get_hash_bucket()
(A) dma_entry_hash
                                                  check_sync()
                       (A) radix_lock()           (W) dma_entry_hash
dma_entry_free()
(W) radix_lock()
                       // CPU2's one
                       (W) rq_lock()CPU1 situation can happen when it extending radix tree and
it tries to wake up kswapd via wake_all_kswapd().CPU2 situation can happen while perf_event_task_sched_out()
(i.e. dma sync operation is called while deleting perf_event using
 etm and etr tmc which are Arm Coresight hwtracing driver backends).To remove this possible situation, call dma_entry_free() after
put_hash_bucket() in check_unmap().