This is a note to let you know that I've just added the patch titled
serial: 8250_dma: Fix DMA Rx rearm race
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
serial-8250_dma-fix-dma-rx-rearm-race.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 57e9af7831dcf211c5c689c2a6f209f4abdf0bce Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@xxxxxxxxxxxxxxx>
Date: Mon, 30 Jan 2023 13:48:41 +0200
Subject: serial: 8250_dma: Fix DMA Rx rearm race
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From: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
commit 57e9af7831dcf211c5c689c2a6f209f4abdf0bce upstream.
As DMA Rx can be completed from two places, it is possible that DMA Rx
completes before DMA completion callback had a chance to complete it.
Once the previous DMA Rx has been completed, a new one can be started
on the next UART interrupt. The following race is possible
(uart_unlock_and_check_sysrq_irqrestore() replaced with
spin_unlock_irqrestore() for simplicity/clarity):
CPU0 CPU1
dma_rx_complete()
serial8250_handle_irq()
spin_lock_irqsave(&port->lock)
handle_rx_dma()
serial8250_rx_dma_flush()
__dma_rx_complete()
dma->rx_running = 0
// Complete DMA Rx
spin_unlock_irqrestore(&port->lock)
serial8250_handle_irq()
spin_lock_irqsave(&port->lock)
handle_rx_dma()
serial8250_rx_dma()
dma->rx_running = 1
// Setup a new DMA Rx
spin_unlock_irqrestore(&port->lock)
spin_lock_irqsave(&port->lock)
// sees dma->rx_running = 1
__dma_rx_complete()
dma->rx_running = 0
// Incorrectly complete
// running DMA Rx
This race seems somewhat theoretical to occur for real but handle it
correctly regardless. Check what is the DMA status before complething
anything in __dma_rx_complete().
Reported-by: Gilles BULOZ <gilles.buloz@xxxxxxxxxxx>
Tested-by: Gilles BULOZ <gilles.buloz@xxxxxxxxxxx>
Fixes: 9ee4b83e51f7 ("serial: 8250: Add support for dmaengine")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230130114841.25749-3-ilpo.jarvinen@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/8250/8250_dma.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
--- a/drivers/tty/serial/8250/8250_dma.c
+++ b/drivers/tty/serial/8250/8250_dma.c
@@ -46,15 +46,23 @@ static void __dma_rx_complete(void *para
struct uart_8250_dma *dma = p->dma;
struct tty_port *tty_port = &p->port.state->port;
struct dma_tx_state state;
+ enum dma_status dma_status;
int count;
- dma->rx_running = 0;
- dmaengine_tx_status(dma->rxchan, dma->rx_cookie, &state);
+ /*
+ * New DMA Rx can be started during the completion handler before it
+ * could acquire port's lock and it might still be ongoing. Don't to
+ * anything in such case.
+ */
+ dma_status = dmaengine_tx_status(dma->rxchan, dma->rx_cookie, &state);
+ if (dma_status == DMA_IN_PROGRESS)
+ return;
count = dma->rx_size - state.residue;
tty_insert_flip_string(tty_port, dma->rx_buf, count);
p->port.icount.rx += count;
+ dma->rx_running = 0;
tty_flip_buffer_push(tty_port);
}
Patches currently in stable-queue which might be from ilpo.jarvinen@xxxxxxxxxxxxxxx are
queue-5.4/serial-8250_dma-fix-dma-rx-rearm-race.patch
queue-5.4/serial-8250_dma-fix-dma-rx-completion-race.patch
