[PATCH 1/5] dma-coherent: serialize reserved memory pool initialization

[Marek Szyprowski]

Multiple devices can share the same "shared-dma-pool" reserved memory
region, in which case the dma_coherent_mem structure is created by the
first device attached to it and stored in rmem->priv. To avoid the
potential race, serialize the check and initialization of rmem->priv
with a mutex.

Fixes: 7bfa5ab6fa1b ("drivers: dma-coherent: add initialization from device tree")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
---
 kernel/dma/coherent.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/coherent.c b/kernel/dma/coherent.c
index 4d0266893bcc..ac62b6bd3d0d 100644
--- a/kernel/dma/coherent.c
+++ b/kernel/dma/coherent.c
@@ -7,6 +7,7 @@
 #include <linux/slab.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/dma-direct.h>
 #include <linux/dma-map-ops.h>
 
@@ -335,10 +336,18 @@ static phys_addr_t dma_reserved_default_memory_base __initdata;
 static phys_addr_t dma_reserved_default_memory_size __initdata;
 #endif
 
+static DEFINE_MUTEX(rmem_dma_mutex);
+
 static int rmem_dma_device_init(struct reserved_mem *rmem, struct device *dev)
 {
-	struct dma_coherent_mem *mem = rmem->priv;
+	struct dma_coherent_mem *mem;
 
+	/*
+	 * Multiple devices can share the same pool and may be probed
+	 * concurrently, so serialize the initialization of rmem->priv.
+	 */
+	guard(mutex)(&rmem_dma_mutex);
+	mem = rmem->priv;
 	if (!mem) {
 		mem = dma_init_coherent_memory(rmem->base, rmem->base,
 					       rmem->size, true);
-- 
2.43.0