If a watchdog driver tells the framework that the device is running, the framework takes care of feeding the watchdog until userspace opens the device. If the userspace application which is supposed to do that never comes up properly, the watchdog is fed indefinitely by the kernel. This can be especially problematic for embedded devices. The existing handle_boot_enabled cmdline parameter/config option partially solves that, but that is only usable for the subset of hardware watchdogs that have (or can be configured by the bootloader to have) a timeout that is sufficient to make it realistic for userspace to come up. Many devices have timeouts of a second, or even less, making handle_boot_enabled insufficient. These patches allow one to set a maximum time for which the kernel will feed the watchdog, thus ensuring that either userspace has come up, or the board gets reset. This allows fallback logic in the bootloader to attempt some recovery (for example, if an automatic update is in progress, it could roll back to the previous version). The patches have been tested on a Raspberry Pi 2 and a Wandboard. A preparatory patch of this series has already been merged (c013b65ad8a1e "watchdog: introduce watchdog_worker_should_ping helper"). On 2017-07-08, Guenter wrote [1] It is sufficiently different to handle_boot_enabled to keep it separate. I am mostly ok with the patch. One comment below. That one comment (regarding the placement of the module_param) has been addressed in this version. There has been some opposition to making the default value of watchdog.open_timeout configurable in Kconfig, but in [2] Guenter said I used to be opposed to it, but it does seem to make some sense to me now after thinking about it. I do hope that these patches can now find their way into the kernel, but if 2/2 is somehow still controversial, please consider just taking 1/2. (I can't help but noting that handle_boot_enabled does get its default value from Kconfig, and nobody complained about that when that option was added). [1] https://patchwork.kernel.org/patch/9754095/ [2] https://patchwork.kernel.org/patch/9754093/ Rasmus Villemoes (2): watchdog: introduce watchdog.open_timeout commandline parameter watchdog: introduce CONFIG_WATCHDOG_OPEN_TIMEOUT Documentation/watchdog/watchdog-parameters.txt | 9 +++++++++ drivers/watchdog/Kconfig | 9 +++++++++ drivers/watchdog/watchdog_dev.c | 27 +++++++++++++++++++++++++- 3 files changed, 44 insertions(+), 1 deletion(-) -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
