Content-Type: multipart/mixed; boundary="===============0113170580064402495==" MIME-Version: 1.0 From: Peter Zijlstra To: lkp@lists.01.org Subject: Re: [trace events] WARNING: CPU: 0 PID: 91 at kernel/sched/core.c:7253 __might_sleep() Date: Wed, 08 Oct 2014 17:48:38 +0200 Message-ID: <20141008154838.GM10832@worktop.programming.kicks-ass.net> In-Reply-To: <20141008110825.58bdb51d@gandalf.local.home> List-Id: --===============0113170580064402495== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On Wed, Oct 08, 2014 at 11:08:25AM -0400, Steven Rostedt wrote: > > Steve, wth is that thing supposed to do? > > = > > set_current_state(TASK_INTERRUPTIBLE); > > while (!kthread_should_stop()) > > schedule(); > > = > > That looks broken alright. It'll revert to a yield() 'spin' loop if it > > ever gets a wakeup for anything other than the kthread_stop(). > > = > > Did you mean to write something like: > > = > > set_current_state(TASK_INTERRUPTIBLE); > > while (!kthread_should_stop()) { > > schedule(); > > set_current_state(TASK_INTERRUPTIBLE); > > } > > __set_current_state(TASK_RUNNING); > > = > > ? > = > Wow, what a blast from the past. That code hasn't been touched since > 2009! > = > Anyway, all that thread did was call test work on each cpu, and then > waits to be killed. It should only get a single wake up and that should > be from the kthread_stop() call. IOW, that loop should never be > executed more than once. > = > What exactly is the bug here? The bug is as explained, the loop is wrong and will revert to a yield 'spin' loop after a single wakeup. The debugging that caught it is that you exit the loop without setting TASK_RUNNING. --===============0113170580064402495==--