[ Upstream commit 8493eab02608b0e82f67b892aa72882e510c31d0 ]
When uart_flush_buffer() is called, the .flush_buffer() callback zeroes the tx_dma_len field. This may race with the work queue function handling transmit DMA requests:
1. If the buffer is flushed before the first DMA API call, dmaengine_prep_slave_single() may be called with a zero length, causing the DMA request to never complete, leading to messages like:
rcar-dmac e7300000.dma-controller: Channel Address Error happen
and, with debug enabled:
sh-sci e6e88000.serial: sci_dma_tx_work_fn: ffff800639b55000: 0...0, cookie 126
and DMA timeouts.
2. If the buffer is flushed after the first DMA API call, but before the second, dma_sync_single_for_device() may be called with a zero length, causing the transmit data not to be flushed to RAM, and leading to stale data being output.
Fix this by: 1. Letting sci_dma_tx_work_fn() return immediately if the transmit buffer is empty, 2. Extending the critical section to cover all DMA preparational work, so tx_dma_len stays consistent for all of it, 3. Using local copies of circ_buf.head and circ_buf.tail, to make sure they match the actual operation above.
Reported-by: Eugeniu Rosca erosca@de.adit-jv.com Suggested-by: Yoshihiro Shimoda yoshihiro.shimoda.uh@renesas.com Signed-off-by: Geert Uytterhoeven geert+renesas@glider.be Reviewed-by: Eugeniu Rosca erosca@de.adit-jv.com Tested-by: Eugeniu Rosca erosca@de.adit-jv.com Link: https://lore.kernel.org/r/20190624123540.20629-2-geert+renesas@glider.be Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/tty/serial/sh-sci.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-)
diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c index 8ec8b3bbaf25..ea35f5144237 100644 --- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -1291,6 +1291,7 @@ static void work_fn_tx(struct work_struct *work) struct uart_port *port = &s->port; struct circ_buf *xmit = &port->state->xmit; dma_addr_t buf; + int head, tail;
/* * DMA is idle now. @@ -1300,16 +1301,23 @@ static void work_fn_tx(struct work_struct *work) * consistent xmit buffer state. */ spin_lock_irq(&port->lock); - buf = s->tx_dma_addr + (xmit->tail & (UART_XMIT_SIZE - 1)); + head = xmit->head; + tail = xmit->tail; + buf = s->tx_dma_addr + (tail & (UART_XMIT_SIZE - 1)); s->tx_dma_len = min_t(unsigned int, - CIRC_CNT(xmit->head, xmit->tail, UART_XMIT_SIZE), - CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE)); - spin_unlock_irq(&port->lock); + CIRC_CNT(head, tail, UART_XMIT_SIZE), + CIRC_CNT_TO_END(head, tail, UART_XMIT_SIZE)); + if (!s->tx_dma_len) { + /* Transmit buffer has been flushed */ + spin_unlock_irq(&port->lock); + return; + }
desc = dmaengine_prep_slave_single(chan, buf, s->tx_dma_len, DMA_MEM_TO_DEV, DMA_PREP_INTERRUPT | DMA_CTRL_ACK); if (!desc) { + spin_unlock_irq(&port->lock); dev_warn(port->dev, "Failed preparing Tx DMA descriptor\n"); /* switch to PIO */ sci_tx_dma_release(s, true); @@ -1319,20 +1327,20 @@ static void work_fn_tx(struct work_struct *work) dma_sync_single_for_device(chan->device->dev, buf, s->tx_dma_len, DMA_TO_DEVICE);
- spin_lock_irq(&port->lock); desc->callback = sci_dma_tx_complete; desc->callback_param = s; - spin_unlock_irq(&port->lock); s->cookie_tx = dmaengine_submit(desc); if (dma_submit_error(s->cookie_tx)) { + spin_unlock_irq(&port->lock); dev_warn(port->dev, "Failed submitting Tx DMA descriptor\n"); /* switch to PIO */ sci_tx_dma_release(s, true); return; }
+ spin_unlock_irq(&port->lock); dev_dbg(port->dev, "%s: %p: %d...%d, cookie %d\n", - __func__, xmit->buf, xmit->tail, xmit->head, s->cookie_tx); + __func__, xmit->buf, tail, head, s->cookie_tx);
dma_async_issue_pending(chan); }