From: Vladimir Oltean <olteanv@gmail.com>

Date: Tue, 3 Sep 2019 13:57:08 +0300

Subject: spi: spi-fsl-dspi: Fix race condition in TCFQ/EOQ interrupt

Git-commit: e327364948492f6a4e866417d3d4d17d95fed285

Patch-mainline: v5.4-rc1

References: bsc#1167260

When the driver is working in TCFQ/EOQ mode (i.e. interacts with the SPI

controller's FIFOs directly) the following sequence of operations

happens:

- The first byte of the tx buffer gets pushed to the TX FIFO (dspi->len

  gets decremented). This triggers the train of interrupts that handle

  the rest of the bytes.

- The dspi_interrupt handles a TX confirmation event. It reads the newly

  available byte from the RX FIFO, checks the dspi->len exit condition,

  and if there's more to be done, it kicks off the next interrupt in the

  train by writing the next byte to the TX FIFO.

Now the problem is that the wait queue is woken up one byte too early,

because dspi->len becomes 0 as soon as the byte has been pushed into the

TX FIFO. Its interrupt has not yet been processed and the RX byte has

not been put from the FIFO into the buffer.

Depending on the timing of the wait queue wakeup vs the handling of the

last dspi_interrupt, it can happen that the main SPI message pump thread

has already returned back into the spi_device driver. When the rx buffer

is on stack (which it can be, because in this mode, the DSPI doesn't do

DMA), the last interrupt will perform a memory write into an rx buffer

that has been freed. This manifests as stack corruption.

The solution is to only wake up the wait queue when dspi_rxtx says so,

i.e. after it has processed the last TX confirmation interrupt and

collected the last RX byte.

Fixes: c55be3059159 ("spi: spi-fsl-dspi: Use poll mode in case the platform IRQ is missing")

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>

Link: https://lore.kernel.org/r/20190903105708.32273-1-olteanv@gmail.com

Signed-off-by: Mark Brown <broonie@kernel.org>

Signed-off-by: Mian Yousaf Kaukab <ykaukab@suse.de>

---

 drivers/spi/spi-fsl-dspi.c | 4 +---

 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c

index 77db43f1290f..bec758e978fb 100644

--- a/drivers/spi/spi-fsl-dspi.c

+++ b/drivers/spi/spi-fsl-dspi.c

@@ -710,9 +710,7 @@ static irqreturn_t dspi_interrupt(int irq, void *dev_id)

 	if (!(spi_sr & (SPI_SR_EOQF | SPI_SR_TCFQF)))

 		return IRQ_NONE;

-	dspi_rxtx(dspi);

-

-	if (!dspi->len) {

+	if (dspi_rxtx(dspi) == 0) {

 		dspi->waitflags = 1;

 		wake_up_interruptible(&dspi->waitq);

 	}

-- 

2.26.2