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    Subject[PATCH v2 1/4] spi: spi-geni-qcom: Fix geni_spi_isr() NULL dereference in timeout case
    Date
    In commit 7ba9bdcb91f6 ("spi: spi-geni-qcom: Don't keep a local state
    variable") we changed handle_fifo_timeout() so that we set
    "mas->cur_xfer" to NULL to make absolutely sure that we don't mess
    with the buffers from the previous transfer in the timeout case.

    Unfortunately, this caused the IRQ handler to dereference NULL in some
    cases. One case:

    CPU0 CPU1
    ---- ----
    setup_fifo_xfer()
    geni_se_setup_m_cmd()
    <hardware starts transfer>
    <transfer completes in hardware>
    <hardware sets M_RX_FIFO_WATERMARK_EN in m_irq>
    ...
    handle_fifo_timeout()
    spin_lock_irq(mas->lock)
    mas->cur_xfer = NULL
    geni_se_cancel_m_cmd()
    spin_unlock_irq(mas->lock)

    geni_spi_isr()
    spin_lock(mas->lock)
    if (m_irq & M_RX_FIFO_WATERMARK_EN)
    geni_spi_handle_rx()
    mas->cur_xfer NULL dereference!

    tl;dr: Seriously delayed interrupts for RX/TX can lead to timeout
    handling setting mas->cur_xfer to NULL.

    Let's check for the NULL transfer in the TX and RX cases and reset the
    watermark or clear out the fifo respectively to put the hardware back
    into a sane state.

    NOTE: things still could get confused if we get timeouts all the way
    through handle_fifo_timeout() and then start a new transfer because
    interrupts from the old transfer / cancel / abort could still be
    pending. A future patch will help this corner case.

    Fixes: 561de45f72bd ("spi: spi-geni-qcom: Add SPI driver support for GENI based QUP")
    Signed-off-by: Douglas Anderson <dianders@chromium.org>
    ---

    Changes in v2:
    - (ptr == NULL) => (!ptr).
    - Addressed loop nits in geni_spi_handle_rx().
    - Commit message rewording from Stephen.

    drivers/spi/spi-geni-qcom.c | 14 ++++++++++++++
    1 file changed, 14 insertions(+)

    diff --git a/drivers/spi/spi-geni-qcom.c b/drivers/spi/spi-geni-qcom.c
    index 25810a7eef10..bf55abbd39f1 100644
    --- a/drivers/spi/spi-geni-qcom.c
    +++ b/drivers/spi/spi-geni-qcom.c
    @@ -354,6 +354,12 @@ static bool geni_spi_handle_tx(struct spi_geni_master *mas)
    unsigned int bytes_per_fifo_word = geni_byte_per_fifo_word(mas);
    unsigned int i = 0;

    + /* Stop the watermark IRQ if nothing to send */
    + if (!mas->cur_xfer) {
    + writel(0, se->base + SE_GENI_TX_WATERMARK_REG);
    + return false;
    + }
    +
    max_bytes = (mas->tx_fifo_depth - mas->tx_wm) * bytes_per_fifo_word;
    if (mas->tx_rem_bytes < max_bytes)
    max_bytes = mas->tx_rem_bytes;
    @@ -396,6 +402,14 @@ static void geni_spi_handle_rx(struct spi_geni_master *mas)
    if (rx_last_byte_valid && rx_last_byte_valid < 4)
    rx_bytes -= bytes_per_fifo_word - rx_last_byte_valid;
    }
    +
    + /* Clear out the FIFO and bail if nowhere to put it */
    + if (mas->cur_xfer == NULL) {
    + while (i++ < DIV_ROUND_UP(rx_bytes, bytes_per_fifo_word))
    + readl(se->base + SE_GENI_RX_FIFOn);
    + return;
    + }
    +
    if (mas->rx_rem_bytes < rx_bytes)
    rx_bytes = mas->rx_rem_bytes;

    --
    2.29.2.684.gfbc64c5ab5-goog
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