[PATCH AUTOSEL 5.10 19/33] dma-debug: fix a possible deadlock on radix_lock

Sasha Levin
2024-11-24T13:54:47Z

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/2WMS7BBSF5OZYB63VT44U5YWLFP5HL6U/#RWM6MLQX5ANBTEQ2PRM7OXCBGCE6NPWU
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 654b039dfc335..d19f610c9eef8 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -1047,9 +1047,13 @@ 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,
--
2.43.0