[PATCH v3 3/4] kdb: Make kdb_printf robust to run in NMI context

From: Sumit Garg <sumit.garg@linaro.org>
To: daniel.thompson@linaro.org
Cc: kgdb-bugreport@lists.sourceforge.net, jason.wessel@windriver.com,
	dianders@chromium.org, pmladek@suse.com,
	sergey.senozhatsky@gmail.com, linux-kernel@vger.kernel.org,
	Sumit Garg <sumit.garg@linaro.org>
Subject: [PATCH v3 3/4] kdb: Make kdb_printf robust to run in NMI context
Date: Wed, 27 May 2020 11:55:58 +0530	[thread overview]
Message-ID: <1590560759-21453-4-git-send-email-sumit.garg@linaro.org> (raw)
In-Reply-To: <1590560759-21453-1-git-send-email-sumit.garg@linaro.org>

While rounding up CPUs via NMIs, its possible that a rounded up CPU
maybe holding a console port lock leading to kgdb master CPU stuck in
a deadlock during invocation of console write operations. So in order
to avoid such a deadlock, enable oops_in_progress prior to invocation
of console handlers.

Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
---
 kernel/debug/kdb/kdb_io.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 349dfcc..f848482 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -566,7 +566,17 @@ static void kdb_msg_write(char *msg, int msg_len)
 	for_each_console(c) {
 		if (!(c->flags & CON_ENABLED))
 			continue;
+		/*
+		 * While rounding up CPUs via NMIs, its possible that
+		 * a rounded up CPU maybe holding a console port lock
+		 * leading to kgdb master CPU stuck in a deadlock during
+		 * invocation of console write operations. So in order
+		 * to avoid such a deadlock, enable oops_in_progress
+		 * prior to invocation of console handlers.
+		 */
+		++oops_in_progress;
 		c->write(c, msg, msg_len);
+		--oops_in_progress;
 		touch_nmi_watchdog();
 	}
 }
-- 
2.7.4

