spi: bcm2835: Fix race on DMA termination

If a DMA transfer finishes orderly right when spi_transfer_one_message()
determines that it has timed out, the callbacks bcm2835_spi_dma_done()
and bcm2835_spi_handle_err() race to call dmaengine_terminate_all(),
potentially leading to double termination.

Prevent by atomically changing the dma_pending flag before calling
dmaengine_terminate_all().

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Fixes: 3ecd37edaa2a ("spi: bcm2835: enable dma modes for transfers meeting certain conditions")
Cc: stable@vger.kernel.org # v4.2+
Cc: Mathias Duckeck <m.duckeck@kunbus.de>
Cc: Frank Pavlic <f.pavlic@kunbus.de>
Cc: Martin Sperl <kernel@martin.sperl.org>
Cc: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c
index 594e971..774161b 100644 (file)
--- a/drivers/spi/spi-bcm2835.c
+++ b/drivers/spi/spi-bcm2835.c
@@ -232,10 +232,9 @@ static void bcm2835_spi_dma_done(void *data)
         * is called the tx-dma must have finished - can't get to this
         * situation otherwise...
         */
-       dmaengine_terminate_all(master->dma_tx);
-
-       /* mark as no longer pending */
-       bs->dma_pending = 0;
+       if (cmpxchg(&bs->dma_pending, true, false)) {
+               dmaengine_terminate_all(master->dma_tx);
+       }
 
        /* and mark as completed */;
        complete(&master->xfer_completion);
@@ -617,10 +616,9 @@ static void bcm2835_spi_handle_err(struct spi_master *master,
        struct bcm2835_spi *bs = spi_master_get_devdata(master);
 
        /* if an error occurred and we have an active dma, then terminate */
-       if (bs->dma_pending) {
+       if (cmpxchg(&bs->dma_pending, true, false)) {
                dmaengine_terminate_all(master->dma_tx);
                dmaengine_terminate_all(master->dma_rx);
-               bs->dma_pending = 0;
        }
        /* and reset */
        bcm2835_spi_reset_hw(master);