linux-kernel - [PATCH AUTOSEL 5.15 22/36] dma-debug: fix a possible deadlock on radix

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Message-ID: <20241124135219.3349183-22-sashal@kernel.org>
Date: Sun, 24 Nov 2024 08:51:36 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Levi Yun <yeoreum.yun@....com>,
	Denis Nikitin <denik@...omium.org>,
	Christoph Hellwig <hch@....de>,
	Sasha Levin <sashal@...nel.org>,
	m.szyprowski@...sung.com,
	iommu@...ts.linux.dev
Subject: [PATCH AUTOSEL 5.15 22/36] dma-debug: fix a possible deadlock on radix_lock

From: Levi Yun <yeoreum.yun@....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@...omium.org>
Closes: https://lists.linaro.org/archives/list/coresight@lists.linaro.org/thread/2WMS7BBSF5OZYB63VT44U5YWLFP5HL6U/#RWM6MLQX5ANBTEQ2PRM7OXCBGCE6NPWU
Signed-off-by: Levi Yun <yeoreum.yun@....com>
Signed-off-by: Christoph Hellwig <hch@....de>
Signed-off-by: Sasha Levin <sashal@...nel.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 09ccb4d6bc7b6..b3961b4ae1696 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -1046,9 +1046,13 @@ 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