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From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: gor@linux.ibm.com, jpoimboe@redhat.com, jikos@kernel.org,
	mbenes@suse.cz, pmladek@suse.com, mingo@kernel.org,
	linux-kernel@vger.kernel.org, joe.lawrence@redhat.com,
	fweisbec@gmail.com, tglx@linutronix.de, hca@linux.ibm.com,
	svens@linux.ibm.com, sumanthk@linux.ibm.com,
	live-patching@vger.kernel.org
Subject: Re: [RFC][PATCH 6/7] context_tracking: Provide SMP ordering using RCU
Date: Wed, 22 Sep 2021 22:02:38 +0200	[thread overview]
Message-ID: <YUuL3sveLOszCDlj@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210922195350.GC880162@paulmck-ThinkPad-P17-Gen-1>

On Wed, Sep 22, 2021 at 12:53:50PM -0700, Paul E. McKenney wrote:

> I wasn't saying that the patch doesn't work.  But doesn't it add an IPI?
> Or was I looking at it too early this morning?

Ah, no. The patch allows a user-bound NOHZ_FULL task to be transitioned
remotely. Unlike today, where they'll eventually poke it with a signal
to force a kernel entry, which is bad m'kay :-)

The code in question skips transitioning running tasks, seeing as you
can't tell what they're doing etc.. Howver, with context tracking on
you're supposedly able to tell they're in userspace without disturbing
them -- except you really can't today.

So if you can tell that a current running task is in userspace (hence my
patch) you can allow the task to transition without any further ado,
userspace is a safe state vs kernel text patching.

  reply	other threads:[~2021-09-22 20:02 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-22 11:05 [RFC][PATCH 0/7] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL cpus Peter Zijlstra
2021-09-22 11:05 ` [RFC][PATCH 1/7] sched,rcu: Rework try_invoke_on_locked_down_task() Peter Zijlstra
2021-09-22 11:05 ` [RFC][PATCH 2/7] sched: Fix task_try_func() Peter Zijlstra
2021-09-22 11:05 ` [RFC][PATCH 3/7] sched,livepatch: Use task_try_func() Peter Zijlstra
2021-09-23 12:05   ` Petr Mladek
2021-09-23 13:17     ` Peter Zijlstra
2021-09-23 13:47       ` Peter Zijlstra
2021-09-22 11:05 ` [RFC][PATCH 4/7] sched: Simplify wake_up_*idle*() Peter Zijlstra
2021-09-22 11:05 ` [RFC][PATCH 5/7] sched,livepatch: Use wake_up_if_idle() Peter Zijlstra
2021-09-22 13:05   ` Miroslav Benes
2021-09-23 12:19     ` Petr Mladek
2021-09-22 11:05 ` [RFC][PATCH 6/7] context_tracking: Provide SMP ordering using RCU Peter Zijlstra
2021-09-22 15:17   ` Paul E. McKenney
2021-09-22 19:33     ` Peter Zijlstra
2021-09-22 19:47       ` Peter Zijlstra
2021-09-22 19:59         ` Paul E. McKenney
2021-09-22 19:53       ` Paul E. McKenney
2021-09-22 20:02         ` Peter Zijlstra [this message]
2021-09-23 12:10   ` Petr Mladek
2021-09-24 18:57   ` Joel Savitz
2021-09-27 14:33     ` Petr Mladek
2021-09-22 11:05 ` [RFC][PATCH 7/7] livepatch,context_tracking: Avoid disturbing NOHZ_FULL tasks Peter Zijlstra
2021-09-23 13:14   ` Petr Mladek
2021-09-23 13:28     ` Peter Zijlstra
2021-09-24  7:33       ` Petr Mladek
2021-09-23 13:22 ` [RFC][PATCH 0/7] sched,rcu,context_tracking,livepatch: Improve livepatch task transitions for idle and NOHZ_FULL cpus Petr Mladek

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