The following sysrq command causes the following lockdep warning:
# echo t > /proc/sysrq-trigger
....
[ 20.325246] ======================================================
[ 20.325252] WARNING: possible circular locking dependency detected
[ 20.325260] 5.15.0-rc2-next-20210924-00004-gd2d6e664f29f-dirty #163
Not tainted
[ 20.325273] ------------------------------------------------------
[ 20.325279] sh/236 is trying to acquire lock:
[ 20.325293] c1618614 (console_owner){-...}-{0:0}, at:
console_unlock+0x180/0x5bc
[ 20.325361]
[ 20.325361] but task is already holding lock:
[ 20.325368] eefccc90 (&pool->lock){-.-.}-{2:2}, at:
show_workqueue_state+0x104/0x3c8
[ 20.325432]
[ 20.325432] which lock already depends on the new lock.
...
[ 20.325657] -> #2 (&pool->lock/1){-.-.}-{2:2}:
[ 20.325690] __queue_work+0x114/0x810
[ 20.325710] queue_work_on+0x54/0x94
[ 20.325727] __imx_uart_rxint.constprop.0+0x1b4/0x2e0
[ 20.325760] imx_uart_int+0x270/0x310
This problem happens because uart_handle_sysrq_char() is called
with the lock held.
Fix this by using the same approach done in commit 5697df7322fe ("serial:
fsl_lpuart: split sysrq handling"), which calls uart_prepare_sysrq_char()
and uart_unlock_and_check_sysrq() instead.
Its commit log says:
"Instead of uart_handle_sysrq_char() use uart_prepare_sysrq_char() and
uart_unlock_and_check_sysrq(). This will call handle_sysrq() without
holding the port lock, which in turn let us drop the spin_trylock hack."
Do the same here to suppress the false positive lockdep warning.
As __imx_uart_rxint() drops the lock now, remove the spin_unlock()
inside imx_uart_rxint(), which is only used on i.MX1.
Tested on a i.MX7D board via 'echo t > /proc/sysrq-trigger' in the
command line and also by passing the "<break> + t" keys in
the serial console.
Signed-off-by: Fabio Estevam <festevam@xxxxxxx>
---
Changes since v2:
- Keep the cast when calling uart_prepare_sysrq_char() - Johan
- Improve commit log and subject - Johan
drivers/tty/serial/imx.c | 15 +++++----------
1 file changed, 5 insertions(+), 10 deletions(-)
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 8b121cd869e9..a0135718c588 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -803,7 +803,7 @@ static irqreturn_t __imx_uart_rxint(int irq, void *dev_id)
continue;
}
- if (uart_handle_sysrq_char(&sport->port, (unsigned char)rx))
+ if (uart_prepare_sysrq_char(&sport->port, (unsigned char)rx))
continue;
if (unlikely(rx & URXD_ERR)) {
@@ -844,6 +844,7 @@ static irqreturn_t __imx_uart_rxint(int irq, void *dev_id)
}
out:
+ uart_unlock_and_check_sysrq(&sport->port);
tty_flip_buffer_push(port);
return IRQ_HANDLED;
@@ -852,15 +853,10 @@ static irqreturn_t __imx_uart_rxint(int irq, void *dev_id)
static irqreturn_t imx_uart_rxint(int irq, void *dev_id)
{
struct imx_port *sport = dev_id;
- irqreturn_t ret;
spin_lock(&sport->port.lock);
- ret = __imx_uart_rxint(irq, dev_id);
-
- spin_unlock(&sport->port.lock);
-
- return ret;
+ return __imx_uart_rxint(irq, dev_id);
}
static void imx_uart_clear_rx_errors(struct imx_port *sport);
@@ -959,6 +955,7 @@ static irqreturn_t imx_uart_int(int irq, void *dev_id)
imx_uart_writel(sport, USR1_AGTIM, USR1);
__imx_uart_rxint(irq, dev_id);
+ spin_lock(&sport->port.lock);
ret = IRQ_HANDLED;
}
@@ -1977,9 +1974,7 @@ imx_uart_console_write(struct console *co, const char *s, unsigned int count)
unsigned int ucr1;
int locked = 1;
- if (sport->port.sysrq)
- locked = 0;
- else if (oops_in_progress)
+ if (oops_in_progress)
locked = spin_trylock_irqsave(&sport->port.lock, flags);
else
spin_lock_irqsave(&sport->port.lock, flags);
--
2.25.1
