FAILED: patch "[PATCH] tty: serial: fsl_lpuart: fix race on RX DMA shutdown" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 1be6f2b15f902c02e055ae0b419ca789200473c9
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '[email protected]' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

1be6f2b15f90 ("tty: serial: fsl_lpuart: fix race on RX DMA shutdown") 8682ab0eea89 ("tty: serial: fsl_lpuart: switch to new dmaengine_terminate_* API") 4f5cb8c5e915 ("tty: serial: fsl_lpuart: enable wakeup source for lpuart") 374e01fa1304 ("serial: fsl_lpuart: Fix comment typo")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1be6f2b15f902c02e055ae0b419ca789200473c9 Mon Sep 17 00:00:00 2001
From: Alexander Sverdlin <[email protected]>
Date: Thu, 9 Mar 2023 14:43:02 +0100
Subject: [PATCH] tty: serial: fsl_lpuart: fix race on RX DMA shutdown

From time to time DMA completion can come in the middle of DMA shutdown:

<process ctx>: <IRQ>:
lpuart32_shutdown()
lpuart_dma_shutdown()

    del_timer_sync()
					lpuart_dma_rx_complete()
					  lpuart_copy_rx_to_tty()
					    mod_timer()
    lpuart_dma_rx_free()

When the timer fires a bit later, sport->dma_rx_desc is NULL:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000004
pc : lpuart_copy_rx_to_tty+0xcc/0x5bc
lr : lpuart_timer_func+0x1c/0x2c
Call trace:
 lpuart_copy_rx_to_tty
 lpuart_timer_func
 call_timer_fn
 __run_timers.part.0
 run_timer_softirq
 __do_softirq
 __irq_exit_rcu
 irq_exit
 handle_domain_irq
 gic_handle_irq
 call_on_irq_stack
 do_interrupt_handler
 ...

To fix this fold del_timer_sync() into lpuart_dma_rx_free() after dmaengine_terminate_sync() to make sure timer will not be re-started in lpuart_copy_rx_to_tty() <= lpuart_dma_rx_complete().

index f9e164abf920..56e6ba3250cd 100644
@@ -1354,6 +1354,7 @@ static void lpuart_dma_rx_free(struct uart_port *port)
 	struct dma_chan *chan = sport->dma_rx_chan;
 
 	dmaengine_terminate_sync(chan);
+	del_timer_sync(&sport->lpuart_timer);
 	dma_unmap_sg(chan->device->dev, &sport->rx_sgl, 1, DMA_FROM_DEVICE);
 	kfree(sport->rx_ring.buf);
 	sport->rx_ring.tail = 0;

@@ -1813,7 +1814,6 @@ static int lpuart32_startup(struct uart_port *port)
 static void lpuart_dma_shutdown(struct lpuart_port *sport)
 {
 	if (sport->lpuart_dma_rx_use) {
-		del_timer_sync(&sport->lpuart_timer);
 		lpuart_dma_rx_free(&sport->port);
 		sport->lpuart_dma_rx_use = false;
 	}

@@ -1973,10 +1973,8 @@ lpuart_set_termios(struct uart_port *port, struct ktermios *termios,
 	 * Since timer function acqures sport->port.lock, need to stop before
 	 * acquring same lock because otherwise del_timer_sync() can deadlock.
 	 */
-	if (old && sport->lpuart_dma_rx_use) {
-		del_timer_sync(&sport->lpuart_timer);
+	if (old && sport->lpuart_dma_rx_use)
 		lpuart_dma_rx_free(&sport->port);
-	}
 
 	spin_lock_irqsave(&sport->port.lock, flags);
 

@@ -2210,10 +2208,8 @@ lpuart32_set_termios(struct uart_port *port, struct ktermios *termios,
 	 * Since timer function acqures sport->port.lock, need to stop before
 	 * acquring same lock because otherwise del_timer_sync() can deadlock.
 	 */
-	if (old && sport->lpuart_dma_rx_use) {
-		del_timer_sync(&sport->lpuart_timer);
+	if (old && sport->lpuart_dma_rx_use)
 		lpuart_dma_rx_free(&sport->port);
-	}
 
 	spin_lock_irqsave(&sport->port.lock, flags);
 

@@ -3020,7 +3016,6 @@ static int lpuart_suspend(struct device *dev)
 			 * cannot resume as expected, hence gracefully release the
 			 * Rx DMA path before suspend and start Rx DMA path on resume.
 			 */
-			del_timer_sync(&sport->lpuart_timer);
 			lpuart_dma_rx_free(&sport->port);
 
 			/* Disable Rx DMA to use UART port as wakeup source */