[PATCH 04/12] i3c: mipi-i3c-hci: Fix race in DMA ring dequeue

[Frank Li]

On Fri, Feb 27, 2026 at 04:11:41PM +0200, Adrian Hunter wrote:
> The HCI DMA dequeue path (hci_dma_dequeue_xfer()) may be invoked for
> multiple transfers that timeout around the same time.  However, the
> function is not serialized and can race with itself.
>
> When a timeout occurs, hci_dma_dequeue_xfer() stops the ring, processes
> incomplete transfers, and then restarts the ring.  If another timeout
> triggers a parallel call into the same function, the two instances may
> interfere with each other - stopping or restarting the ring at unexpected
> times.

how to sync with another hci_dma_queue_xfer()?

Frank

>
> Add a mutex so that hci_dma_dequeue_xfer() is serialized with respect to
> itself.
>
> Fixes: 9ad9a52cce282 ("i3c/master: introduce the mipi-i3c-hci driver")
> Cc: stable at vger.kernel.org
> Signed-off-by: Adrian Hunter <adrian.hunter at intel.com>
> ---
>  drivers/i3c/master/mipi-i3c-hci/dma.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/i3c/master/mipi-i3c-hci/dma.c b/drivers/i3c/master/mipi-i3c-hci/dma.c
> index f60654fbe58e..5a9af561e4cb 100644
> --- a/drivers/i3c/master/mipi-i3c-hci/dma.c
> +++ b/drivers/i3c/master/mipi-i3c-hci/dma.c
> @@ -133,6 +133,7 @@ struct hci_rh_data {
>  	struct hci_xfer **src_xfers;
>  	spinlock_t lock;
>  	struct completion op_done;
> +	struct mutex control_mutex;
>  };
>
>  struct hci_rings_data {
> @@ -347,6 +348,7 @@ static int hci_dma_init(struct i3c_hci *hci)
>  		rh->regs = hci->base_regs + offset;
>  		spin_lock_init(&rh->lock);
>  		init_completion(&rh->op_done);
> +		mutex_init(&rh->control_mutex);
>
>  		rh->xfer_entries = XFER_RING_ENTRIES;
>
> @@ -549,6 +551,8 @@ static bool hci_dma_dequeue_xfer(struct i3c_hci *hci,
>  	unsigned int i;
>  	bool did_unqueue = false;
>
> +	guard(mutex)(&rh->control_mutex);
> +
>  	/* stop the ring */
>  	rh_reg_write(RING_CONTROL, RING_CTRL_ABORT);
>  	if (wait_for_completion_timeout(&rh->op_done, HZ) == 0) {
> --
> 2.51.0
>
>
> --
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