[PATCH 5.15.y v3 1/4] ipmi:ssif: Fix a shutdown race

[Corey Minyard <corey@minyard.net>]

It was possible for the SSIF thread to stop and quit before the
kthread_stop() call because ssif->stopping was set before the
stop.  So only exit the SSIF thread is kthread_should_stop()
returns true.

In the mainstream kernel this was fixed in 6bd0eb6d759b ("ipmi:ssif:
Fix a shutdown race").  However, that requires a fix in kernel
version 6.1 has a fix to kthread stop to cause interruptible waits
to return -ERESTARTSYS on a stop.  This has not been backported to
older kernels, and that would probably be a bad idea.  But it means
that the mainstrem kernel fix for this will not work.

Instead, wait for kthread_should_stop() to return true before exiting
the thread.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
---
 drivers/char/ipmi/ipmi_ssif.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/char/ipmi/ipmi_ssif.c b/drivers/char/ipmi/ipmi_ssif.c
index 30f757249c5c..430302d2da6e 100644
--- a/drivers/char/ipmi/ipmi_ssif.c
+++ b/drivers/char/ipmi/ipmi_ssif.c
@@ -513,6 +513,16 @@ static int ipmi_ssif_thread(void *data)
 		}
 	}
 
+	/*
+	 * The thread can break out of the loop if stopping is set,
+	 * and this can be before kthread_stop() gets called and thus
+	 * kthread_should_stop() will not be set.  This can cause
+	 * spinning calling this function and other bad things.  So
+	 * wait for kthread_should_stop() to be set.
+	 */
+	while (!kthread_should_stop())
+		msleep_interruptible(1);
+
 	return 0;
 }
 
-- 
2.43.0