[PATCH v2] watchdog: make open-write-close-open functionality a config knob
Rasmus Villemoes
rasmus.villemoes at prevas.dk
Fri Mar 26 09:31:56 UTC 2021
The behaviour introduced by commit 31c765081dc4 ("watchdog: stop
watchdog first on startup") causes warnings in the kernel log when the
nowayout feature is enabled:
[ 16.212184] watchdog: watchdog0: nowayout prevents watchdog being stopped!
[ 16.212196] watchdog: watchdog0: watchdog did not stop!
The latter may also appear by itself in case the watchdog is of the
type that cannot be stopped once started (e.g. the common
always-running gpio_wdt kind).
These warnings can be somewhat ominous and distracting, so allow
configuring whether to use this open-write-close-open sequence rather
than just open. Also saves a bit of .text when disabled:
function old new delta
shutdown_on_signal 31 58 +27
watchdog_main 339 306 -33
shutdown_watchdog 34 - -34
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 1/1 up/down: 27/-67) Total: -40 bytes
Make it default n:
- It's a workaround for one specific type of watchdog (and
that seems to be a defect in the kernel driver)
- Even when not enabled in busybox config, it can easily be
implemented outside busybox
- Code size
- Commit 31c765081dc4 should be considered a regression for all the
boards that now end up with KERN_CRIT warnings in dmesg.
- The author of that commit said "This use case is evidently rare, so
if it is indeed causing problems for other people I'd OK then I
understand whatever needs to be done." in the v1 thread.
Cc: Matt Spinler <mspinler at linux.vnet.ibm.com>
Cc: deweloper at wp.pl
Signed-off-by: Rasmus Villemoes <rasmus.villemoes at prevas.dk>
---
miscutils/watchdog.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/miscutils/watchdog.c b/miscutils/watchdog.c
index 0ed10bcf1..c2ee06dcf 100644
--- a/miscutils/watchdog.c
+++ b/miscutils/watchdog.c
@@ -18,6 +18,21 @@
//config: watchdog applet ever fails to write the magic character within a
//config: certain amount of time, the watchdog device assumes the system has
//config: hung, and will cause the hardware to reboot.
+//config:
+//config:config FEATURE_WATCHDOG_OPEN_TWICE
+//config: bool "Open watchdog device twice, closing it gracefully in between"
+//config: depends on WATCHDOG
+//config: default n
+//config: help
+//config: When enabled, the watchdog device is opened and then immediately
+//config: magic-closed, before being opened a second time. This may be necessary
+//config: for some watchdog devices, but can cause spurious warnings in the
+//config: kernel log if the nowayout feature is enabled. Also, if this workaround
+//config: is really needed for you machine to work properly, consider whether
+//config: it should be fixed in the kernel driver instead. Even when disabled,
+//config: the behaviour is easily emulated with a "printf 'V' > /dev/watchdog"
+//config: immediately before starting the busybox watchdog daemnn. Say n unless
+//config: you know that you absolutely need this.
//applet:IF_WATCHDOG(APPLET(watchdog, BB_DIR_SBIN, BB_SUID_DROP))
@@ -73,6 +88,7 @@ static void watchdog_open(const char* device)
/* Use known fd # - avoid needing global 'int fd' */
xmove_fd(xopen(device, O_WRONLY), 3);
+#if ENABLE_FEATURE_WATCHDOG_OPEN_TWICE
/* If the watchdog driver can do something other than cause a reboot
* on a timeout, then it's possible this program may be starting from
* a state when the watchdog hadn't been previously stopped with
@@ -82,6 +98,7 @@ static void watchdog_open(const char* device)
shutdown_watchdog();
xmove_fd(xopen(device, O_WRONLY), 3);
+#endif
}
int watchdog_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
--
2.29.2
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