4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Lukas Wunner <lu...@wunner.de>

commit e82b0b3828451c1cd331d9f304c6078fcd43b62e upstream.

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 <lu...@wunner.de>
Fixes: 3ecd37edaa2a ("spi: bcm2835: enable dma modes for transfers meeting 
certain conditions")
Cc: sta...@vger.kernel.org # v4.2+
Cc: Mathias Duckeck <m.duck...@kunbus.de>
Cc: Frank Pavlic <f.pav...@kunbus.de>
Cc: Martin Sperl <ker...@martin.sperl.org>
Cc: Noralf Trønnes <nor...@tronnes.org>
Signed-off-by: Mark Brown <broo...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/spi/spi-bcm2835.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

--- a/drivers/spi/spi-bcm2835.c
+++ b/drivers/spi/spi-bcm2835.c
@@ -233,10 +233,9 @@ static void bcm2835_spi_dma_done(void *d
         * 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(struc
        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);


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