Messages in this thread | | | Date | Tue, 21 May 2013 13:19:17 +0530 | From | "Srivatsa S. Bhat" <> | Subject | Re: [RFC PATCH 6/8] kthread: Enable parking requests from setup() and unpark() callbacks |
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On 05/21/2013 11:04 AM, anish singh wrote: > On Mon, May 20, 2013 at 9:31 PM, Frederic Weisbecker <fweisbec@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
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