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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Simon Horman <horms+renesas@verge.net.au>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.20 182/352] serial: sh-sci: Fix locking in sci_submit_rx()
Date:   Mon, 11 Feb 2019 15:16:49 +0100
Message-Id: <20190211141858.671251270@linuxfoundation.org>
In-Reply-To: <20190211141846.543045703@linuxfoundation.org>
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4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit dd1f2250da95e87cb3e612858f94b14f99445a7c ]

Some callers of sci_submit_rx() hold the port spinlock, others don't.
During fallback to PIO, the driver needs to obtain the port spinlock.
If the lock was already held, spinlock recursion is detected, causing a
deadlock: BUG: spinlock recursion on CPU#0.

Fix this by adding a flag parameter to sci_submit_rx() for the caller to
indicate the port spinlock is already held, so spinlock recursion can be
avoided.

Move the spin_lock_irqsave() up, so all DMA disable steps are protected,
which is safe as the recently introduced dmaengine_terminate_async() can
be called in atomic context.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/sh-sci.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index cc56cb3b3eca..613007d7165e 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -1331,7 +1331,7 @@ static void sci_tx_dma_release(struct sci_port *s)
 	dma_release_channel(chan);
 }
 
-static void sci_submit_rx(struct sci_port *s)
+static void sci_submit_rx(struct sci_port *s, bool port_lock_held)
 {
 	struct dma_chan *chan = s->chan_rx;
 	struct uart_port *port = &s->port;
@@ -1362,16 +1362,18 @@ static void sci_submit_rx(struct sci_port *s)
 	return;
 
 fail:
+	/* Switch to PIO */
+	if (!port_lock_held)
+		spin_lock_irqsave(&port->lock, flags);
 	if (i)
 		dmaengine_terminate_async(chan);
 	for (i = 0; i < 2; i++)
 		s->cookie_rx[i] = -EINVAL;
 	s->active_rx = -EINVAL;
-	/* Switch to PIO */
-	spin_lock_irqsave(&port->lock, flags);
 	s->chan_rx = NULL;
 	sci_start_rx(port);
-	spin_unlock_irqrestore(&port->lock, flags);
+	if (!port_lock_held)
+		spin_unlock_irqrestore(&port->lock, flags);
 }
 
 static void work_fn_tx(struct work_struct *work)
@@ -1491,7 +1493,7 @@ static enum hrtimer_restart rx_timer_fn(struct hrtimer *t)
 	}
 
 	if (port->type == PORT_SCIFA || port->type == PORT_SCIFB)
-		sci_submit_rx(s);
+		sci_submit_rx(s, true);
 
 	/* Direct new serial port interrupts back to CPU */
 	scr = serial_port_in(port, SCSCR);
@@ -1617,7 +1619,7 @@ static void sci_request_dma(struct uart_port *port)
 		s->chan_rx_saved = s->chan_rx = chan;
 
 		if (port->type == PORT_SCIFA || port->type == PORT_SCIFB)
-			sci_submit_rx(s);
+			sci_submit_rx(s, false);
 	}
 }
 
@@ -1667,7 +1669,7 @@ static irqreturn_t sci_rx_interrupt(int irq, void *ptr)
 			scr |= SCSCR_RDRQE;
 		} else {
 			scr &= ~SCSCR_RIE;
-			sci_submit_rx(s);
+			sci_submit_rx(s, false);
 		}
 		serial_port_out(port, SCSCR, scr);
 		/* Clear current interrupt */
-- 
2.19.1