Hi Ahmad, >Hi George, > On 05.03.25 11:10, George Cherian wrote: >> This series adds a new kernel command line option to watchdog core to >> stop the watchdog on panic. This is useul in certain systems which prevents >> successful loading of kdump kernel due to watchdog reset. >> >> Some of the watchdog drivers stop function could sleep. For such >> drivers the stop_on_panic is not valid as the notifier callback happens >> in atomic context. Introduce WDIOF_STOP_MAYSLEEP flag to watchdog_info >> options to indicate whether the stop function would sleep. > >Did you consider having a reset_on_panic instead, which sets a user-specified >timeout on panic? This would make the mechanism useful also for watchdogs /proc/sys/kernel/panic already provides that support. You may echo a non-zero value and the system tries for a soft reboot after those many seconds. But this doesn't happen in case of a kdump kernel load after panic. >that can't be disabled and would protect against system lock up: >Consider a memory-corruption bug (perhaps externally via DMA), which partially >overwrites both main and kdump kernel. With a disabled watchdog, the system >may not be able to recover on its own. Yes, that is the reason why the kernel command-line is optional and by default it is set to zero. So that in cases if you have a corrupted kdump kernel then watchdog kicks in. > >If you did consider it, what made you decide against it? watchdog.stop_on_panic=1 is specifically for systems which can't boot a kdump kernel due to the fact that the kdump kernel gets a watchdog reset while booting, may be due to a shorter watchdog time. For eg: a 32-bit watchdog down counter running at 1GHz. reset_on_panic can guarantee only the largest watchdog timeout supported by HW, since there is no one to ping the watchdog. > >Thanks, >Ahmad > >> >> > Changelog: > v1 -> v2 > - Remove the per driver flag setting option > - Take the parameter via kernel command-line parameter to watchdog_core. > > v2 -> v3 > - Remove the helper function watchdog_stop_on_panic() from watchdog.h. > - There are no users for this. > > v3 -> v4 > - Since the panic notifier is in atomic context, watchdog functions > which sleep can't be called. > - Add an options flag WDIOF_STOP_MAYSLEEP to indicate whether stop > function sleeps. > - Simplify the stop_on_panic kernel command line parsing. > - Enable the panic notiffier only if the watchdog stop function doesn't > sleep > > George Cherian (2): > watchdog: Add a new flag WDIOF_STOP_MAYSLEEP > drivers: watchdog: Add support for panic notifier callback - George
