[PATCH 5.9 010/252] lan743x: prevent entire kernel HANG on open, for some platforms

Greg Kroah-Hartman
2020-11-23T12:41:40Z

From: Sven Van Asbroeck <thesven73@gmail.com>

[ Upstream commit 796a2665ca3e91ebaba7222f76fd9a035714e2d8 ]

On arm imx6, when opening the chip's netdev, the whole Linux
kernel intermittently hangs/freezes.

This is caused by a bug in the driver code which tests if pcie
interrupts are working correctly, using the software interrupt:

1. open: enable the software interrupt
2. open: tell the chip to assert the software interrupt
3. open: wait for flag
4. ISR: acknowledge s/w interrupt, set flag
5. open: notice flag, disable the s/w interrupt, continue

Unfortunately the ISR only acknowledges the s/w interrupt, but
does not disable it. This will re-trigger the ISR in a tight
loop.

On some (lucky) platforms, open proceeds to disable the s/w
interrupt even while the ISR is 'spinning'. On arm imx6,
the spinning ISR does not allow open to proceed, resulting
in a hung Linux kernel.

Fix minimally by disabling the s/w interrupt in the ISR, which
will prevent it from spinning. This won't break anything because
the s/w interrupt is used as a one-shot interrupt.

Note that this is a minimal fix, overlooking many possible
cleanups, e.g.:
- lan743x_intr_software_isr() is completely redundant and reads
INT_STS twice for no apparent reason
- disabling the s/w interrupt in lan743x_intr_test_isr() is now
redundant, but harmless
- waiting on software_isr_flag can be converted from a sleeping
poll loop to wait_event_timeout()

Fixes: 23f0703c125b ("lan743x: Add main source files for new lan743x driver")
Tested-by: Sven Van Asbroeck <thesven73@gmail.com> # arm imx6 lan7430
Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com>
Link: https://lore.kernel.org/r/20201112204741.12375-1-TheSven73@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/ethernet/microchip/lan743x_main.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/net/ethernet/microchip/lan743x_main.c
+++ b/drivers/net/ethernet/microchip/lan743x_main.c
@@ -148,7 +148,8 @@ static void lan743x_intr_software_isr(vo

int_sts = lan743x_csr_read(adapter, INT_STS);
if (int_sts & INT_BIT_SW_GP_) {
- lan743x_csr_write(adapter, INT_STS, INT_BIT_SW_GP_);
+ /* disable the interrupt to prevent repeated re-triggering */
+ lan743x_csr_write(adapter, INT_EN_CLR, INT_BIT_SW_GP_);
intr->software_isr_flag = 1;
}
}