The patch spi: spi-fsl-dspi: Fix race condition in TCFQ/EOQ interrupt has been applied to the spi tree at https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-5.4 All being well this means that it will be integrated into the linux-next tree (usually sometime in the next 24 hours) and sent to Linus during the next merge window (or sooner if it is a bug fix), however if problems are discovered then the patch may be dropped or reverted. You may get further e-mails resulting from automated or manual testing and review of the tree, please engage with people reporting problems and send followup patches addressing any issues that are reported if needed. If any updates are required or you are submitting further changes they should be sent as incremental updates against current git, existing patches will not be replaced. Please add any relevant lists and maintainers to the CCs when replying to this mail. Thanks, Mark >From e327364948492f6a4e866417d3d4d17d95fed285 Mon Sep 17 00:00:00 2001 From: Vladimir Oltean <olteanv@xxxxxxxxx> Date: Tue, 3 Sep 2019 13:57:08 +0300 Subject: [PATCH] spi: spi-fsl-dspi: Fix race condition in TCFQ/EOQ interrupt 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@xxxxxxxxx> Link: https://lore.kernel.org/r/20190903105708.32273-1-olteanv@xxxxxxxxx Signed-off-by: Mark Brown <broonie@xxxxxxxxxx> --- 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); } -- 2.20.1