From: Aaro Koskinen <aaro.koski...@nokia.com>
There is a narrow window where the SVC kthread may go to sleep with the
maximum (infinite) timeout, missing the wakeup/shutdown from the client
and making the client hang:
Client process SVC kthread
============== ===========
stratix10_svc_done()
while (!kthread_should_stop())
kthread_stop();
ret_fifo = kfifo_out_spinlocked();
wake_up_process();
/* kthread is already running. */
wait_for_completion();
if (!ret_fifo)
/* kthread going to sleep and nobody
* will wake it up unless there is a
* timeout. */
schedule_timeout_interruptible();
/* Client waits for the
* kthread to wake up and
* stop. */
The race window is quite narrow, so in normal use the hang is difficult
to reproduce. The following artificial method was used to trigger a hang
with stratix01-rsu driver and write to "reboot_image":
- Create 100% background CPU load (e.g. "while :; do true; done &"
multiple times).
- Insert busy-looping mdelay(1000) to the kernel thread just before
schedule_timeout_interruptible(). This does not change the program
logic, just timing.
- Now write to "reboot_image", it should hang instantly.
- Examining stack traces, the client process is shown as stuck in
kthread_stop() and kthread remains sleeping and scheduled out as
predicted:
# cat /proc/493/stack
[<0>] __switch_to+0xe0/0x15c
[<0>] kthread_stop+0x9c/0x270
[<0>] stratix10_svc_done+0x58/0xd0
[<0>] rsu_send_msg+0xa0/0x120
[<0>] reboot_image_store+0x9c/0xe0
[<0>] dev_attr_store+0x24/0x40
[<0>] sysfs_kf_write+0x50/0x60
[<0>] kernfs_fop_write_iter+0x124/0x1b4
[<0>] new_sync_write+0xf0/0x190
[<0>] vfs_write+0x21c/0x280
[<0>] ksys_write+0x74/0x100
[<0>] __arm64_sys_write+0x28/0x3c
[<0>] el0_svc_common.constprop.0+0x9c/0x210
[<0>] do_el0_svc+0x78/0xa0
[<0>] el0_svc+0x20/0x30
[<0>] el0_sync_handler+0x1a4/0x1b0
[<0>] el0_sync+0x180/0x1c0
# cat /proc/494/stack
[<0>] __switch_to+0xe0/0x15c
[<0>] svc_normal_to_secure_thread+0x5d8/0x1430
[<0>] kthread+0x150/0x160
[<0>] ret_from_fork+0x10/0x3c
As a workaround, make the kthread to poll for stopped status once a
second instead going to an infinite sleep.
Upstream-Status: Pending
Signed-off-by: Aaro Koskinen <aaro.koski...@nokia.com>
[patch provided by Nokia directly]
Signed-off-by: Liwei Song <liwei.s...@windriver.com>
---
drivers/firmware/stratix10-svc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/firmware/stratix10-svc.c b/drivers/firmware/stratix10-svc.c
index 65a566cba99a..2aae36906616 100644
--- a/drivers/firmware/stratix10-svc.c
+++ b/drivers/firmware/stratix10-svc.c
@@ -552,7 +552,7 @@ static int svc_normal_to_secure_thread(void *data)
&chan->svc_fifo_lock);
if (!ret_fifo) {
- schedule_timeout_interruptible(MAX_SCHEDULE_TIMEOUT);
+ schedule_timeout_interruptible(HZ);
continue;
}
--
2.35.5
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