linux-kernel - [PATCH v2] kdb: use ktime_get_mono_fast_ns() instead of ktime_get

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Message-Id: <3f15868475cb4b32353885ee03c983209279fa81.1517192387.git.baolin.wang@linaro.org>
Date:   Mon, 29 Jan 2018 10:22:51 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     jason.wessel@...driver.com, daniel.thompson@...aro.org
Cc:     mingo@...nel.org, arnd@...db.de, broonie@...nel.org,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: [PATCH v2] kdb: use ktime_get_mono_fast_ns() instead of ktime_get_ts()

The kdb code will print the monotonic time by ktime_get_ts(), but
the ktime_get_ts() will be protected by a sequence lock, that will
introduce one deadlock risk if the lock was already held in the
context from which we entered the debugger.

Thus we can use the ktime_get_mono_fast_ns() to get the monotonic
time, which is NMI safe access to clock monotonic. Moreover we can
remove the 'struct timespec', which is not y2038 safe.

Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
---
Changes since v1:
 - Use ktime_get_mono_fast_ns() instead of ktime_get_seconds().
---
 kernel/debug/kdb/kdb_main.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 69e70f4..bf1d0e0 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -2486,10 +2486,10 @@ static int kdb_kill(int argc, const char **argv)
  */
 static void kdb_sysinfo(struct sysinfo *val)
 {
-	struct timespec uptime;
-	ktime_get_ts(&uptime);
+	u64 uptime = ktime_get_mono_fast_ns();
+
 	memset(val, 0, sizeof(*val));
-	val->uptime = uptime.tv_sec;
+	val->uptime = div_u64(uptime, NSEC_PER_SEC);
 	val->loads[0] = avenrun[0];
 	val->loads[1] = avenrun[1];
 	val->loads[2] = avenrun[2];
-- 
1.7.9.5