spi: tegra210-quad: Protect curr_xfer check in IRQ handler

Now that all other accesses to curr_xfer are done under the lock,
protect the curr_xfer NULL check in tegra_qspi_isr_thread() with the
spinlock. Without this protection, the following race can occur:

  CPU0 (ISR thread)              CPU1 (timeout path)
  ----------------               -------------------
  if (!tqspi->curr_xfer)
    // sees non-NULL
                                 spin_lock()
                                 tqspi->curr_xfer = NULL
                                 spin_unlock()
  handle_*_xfer()
    spin_lock()
    t = tqspi->curr_xfer  // NULL!
    ... t->len ...        // NULL dereference!

With this patch, all curr_xfer accesses are now properly synchronized.

Although all accesses to curr_xfer are done under the lock, in
tegra_qspi_isr_thread() it checks for NULL, releases the lock and
reacquires it later in handle_cpu_based_xfer()/handle_dma_based_xfer().
There is a potential for an update in between, which could cause a NULL
pointer dereference.

To handle this, add a NULL check inside the handlers after acquiring
the lock. This ensures that if the timeout path has already cleared
curr_xfer, the handler will safely return without dereferencing the
NULL pointer.

Fixes: b4e002d8a7ce ("spi: tegra210-quad: Fix timeout handling")
Signed-off-by: Breno Leitao <leitao@debian.org>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://patch.msgid.link/20260126-tegra_xfer-v2-6-6d2115e4f387@debian.org
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-tegra210-quad.c b/drivers/spi/spi-tegra210-quad.c
index 79aeb80aa4a709aedad0ae125d307471a0b3ff97..f425d62e0c276a553a6c6f8fac313369fb409128 100644 (file)
--- a/drivers/spi/spi-tegra210-quad.c
+++ b/drivers/spi/spi-tegra210-quad.c
@@ -1457,6 +1457,11 @@ static irqreturn_t handle_cpu_based_xfer(struct tegra_qspi *tqspi)
        spin_lock_irqsave(&tqspi->lock, flags);
        t = tqspi->curr_xfer;
 
+       if (!t) {
+               spin_unlock_irqrestore(&tqspi->lock, flags);
+               return IRQ_HANDLED;
+       }
+
        if (tqspi->tx_status ||  tqspi->rx_status) {
                tegra_qspi_handle_error(tqspi);
                complete(&tqspi->xfer_completion);
@@ -1527,6 +1532,11 @@ static irqreturn_t handle_dma_based_xfer(struct tegra_qspi *tqspi)
        spin_lock_irqsave(&tqspi->lock, flags);
        t = tqspi->curr_xfer;
 
+       if (!t) {
+               spin_unlock_irqrestore(&tqspi->lock, flags);
+               return IRQ_HANDLED;
+       }
+
        if (num_errors) {
                tegra_qspi_dma_unmap_xfer(tqspi, t);
                tegra_qspi_handle_error(tqspi);
@@ -1565,6 +1575,7 @@ exit:
 static irqreturn_t tegra_qspi_isr_thread(int irq, void *context_data)
 {
        struct tegra_qspi *tqspi = context_data;
+       unsigned long flags;
        u32 status;
 
        /*
@@ -1582,7 +1593,9 @@ static irqreturn_t tegra_qspi_isr_thread(int irq, void *context_data)
         * If no transfer is in progress, check if this was a real interrupt
         * that the timeout handler already processed, or a spurious one.
         */
+       spin_lock_irqsave(&tqspi->lock, flags);
        if (!tqspi->curr_xfer) {
+               spin_unlock_irqrestore(&tqspi->lock, flags);
                /* Spurious interrupt - transfer not ready */
                if (!(status & QSPI_RDY))
                        return IRQ_NONE;
@@ -1599,7 +1612,14 @@ static irqreturn_t tegra_qspi_isr_thread(int irq, void *context_data)
                tqspi->rx_status = tqspi->status_reg & (QSPI_RX_FIFO_OVF | QSPI_RX_FIFO_UNF);
 
        tegra_qspi_mask_clear_irq(tqspi);
+       spin_unlock_irqrestore(&tqspi->lock, flags);
 
+       /*
+        * Lock is released here but handlers safely re-check curr_xfer under
+        * lock before dereferencing.
+        * DMA handler also needs to sleep in wait_for_completion_*(), which
+        * cannot be done while holding spinlock.
+        */
        if (!tqspi->is_curr_dma_xfer)
                return handle_cpu_based_xfer(tqspi);