linux-kernel - [PATCH 6/6] spi: tegra210-quad: Protect curr

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Message-Id: <20260116-tegra_xfer-v1-6-02d96c790619@debian.org>
Date: Fri, 16 Jan 2026 02:41:46 -0800
From: Breno Leitao <leitao@...ian.org>
To: Thierry Reding <thierry.reding@...il.com>, 
 Jonathan Hunter <jonathanh@...dia.com>, 
 Sowjanya Komatineni <skomatineni@...dia.com>, 
 Laxman Dewangan <ldewangan@...dia.com>, Mark Brown <broonie@...nel.org>, 
 Vishwaroop A <va@...dia.com>
Cc: Thierry Reding <treding@...dia.com>, linux-tegra@...r.kernel.org, 
 linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Breno Leitao <leitao@...ian.org>, kernel-team@...a.com, puranjay@...nel.org, 
 usamaarif642@...il.com
Subject: [PATCH 6/6] 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@...ian.org>
---
 drivers/spi/spi-tegra210-quad.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/spi/spi-tegra210-quad.c b/drivers/spi/spi-tegra210-quad.c
index 79aeb80aa4a7..c0443c986dd9 100644
--- 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 @@ static irqreturn_t handle_dma_based_xfer(struct tegra_qspi *tqspi)
 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 +1612,12 @@ 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);
 
+	/*
+	 *  TODO: Keep tqspi->lock held for both handle functions below to avoid
+	 *  releasing and reacquiring the lock between calls.
+	 */
 	if (!tqspi->is_curr_dma_xfer)
 		return handle_cpu_based_xfer(tqspi);
 

-- 
2.47.3