lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Wed, 12 Apr 2017 12:43:09 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Peter Zijlstra <peterz@...radead.org> Cc: LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Subject: Re: [RFC][PATCH] sched: Have do_idle() call __schedule() without enabling preemption On Wed, 12 Apr 2017 18:21:57 +0200 Peter Zijlstra <peterz@...radead.org> wrote: > On Wed, Apr 12, 2017 at 10:41:24AM -0400, Steven Rostedt wrote: > > [ tl;dr; version ] > > > > Peter, In order to have synchronize_rcu_tasks() work, the idle task can > > never be preempted. There's a very small window in > > schedule_preempt_disable() that enables preemption, and when this > > happens, it breaks synchronize_rcu_tasks() (see above email for > > details). > > > > Is there any reason to enable preemption, or can we simply have idle > > call into schedule without ever allowing it to be preempted, as in my > > patch? > > Dunno,.. this changelog should convince me, not make me do the work :-) I didn't want you to do any work. I was wondering if you knew of any reason. But looking into the history of the do_idle() function and schedule_preempt_disable(), I don't see any reason. I'll post another patch with a better change log. > > > Note, it is almost good enough to just change > > schedule_preempt_disable() to do the exact same thing, but there's one > > instance in kernel/locking/mutex.c that calls it in a non running state. > > The point being that that must not happen because of > sched_submit_work(), which, for idle, should not matter. Right, and also for all the other cases that call schedule_preempt_disable() which includes init/main.c and another location in mutex.c that sets the task state to TASK_RUNNING just before calling it. But the one case where it can be something other than TASK_RUNNING, then we need to keep the current method. OK, I think it is fine for the idle task to never enable preemption and I'll post a better change log patch. Thanks! -- Steve
Powered by blists - more mailing lists