On 05/21/2013 11:04 AM, anish singh wrote: > On Mon, May 20, 2013 at 9:31 PM, Frederic Weisbecker <fweis...@gmail.com> > wrote: >> When the watchdog code is boot-disabled by the user, for example >> through the 'nmi_watchdog=0' boot option, the setup() callback of >> the watchdog kthread requests to park the task, and that until the >> user later re-enables the watchdog through sysctl or procfs. >> >> However the parking request is not well handled when done from >> the setup() callback. After ->setup() is called, the generic smpboot >> kthread loop directly tries to call the thread function or wait >> for some event if ->thread_should_run() is false. >> >> In the case of the watchdog kthread, ->thread_should_run() returns >> false and the kthread goes to sleep and wait for the watchdog timer >> to wake it up. But the timer is not enabled since the user requested >> to disable the watchdog. We want the kthread to park instead of waiting >> for events that can't happen. >> >> As a result, later unpark requests after sysctl write through >> 'sysctl -w kernel.watchdog=1' won't wake up/unpark the task as >> expected, since it's not parked anyway, leaving the value modified >> without triggering any action. > Out of curiosity, this can happen only for short period of time right?After > some time this will work right as the thread get back in action > after the schedule call.Then sysctl and procfs will work I think.
kthread_unpark() can wake up a task only if the task is in TASK_PARKED state. But since the above task would be in TASK_INTERRUPTIBLE state (since it is not parked), kthread_unpark() will be powerless to do anything. Regards, Srivatsa S. Bhat -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
