6.6-stable review patch. If anyone has any objections, please let me know.
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From: Levi Yun yeoreum.yun@arm.com
[ Upstream commit 7543c3e3b9b88212fcd0aaf5cab5588797bdc7de ]
radix_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().
Reported-by: Denis Nikitin denik@chromium.org Closes: https://lists.linaro.org/archives/list/coresight@lists.linaro.org/thread/2WM... Signed-off-by: Levi Yun yeoreum.yun@arm.com Signed-off-by: Christoph Hellwig hch@lst.de Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/dma/debug.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c index e472cc37d7de4..958d4aa77dcad 100644 --- a/kernel/dma/debug.c +++ b/kernel/dma/debug.c @@ -1051,9 +1051,13 @@ static void check_unmap(struct dma_debug_entry *ref) }
hash_bucket_del(entry); - dma_entry_free(entry); - put_hash_bucket(bucket, flags); + + /* + * Free the entry outside of bucket_lock to avoid ABBA deadlocks + * between that and radix_lock. + */ + dma_entry_free(entry); }
static void check_for_stack(struct device *dev,