From: Peter Zijlstra <peterz@infradead.org>
To: Petr Mladek <pmladek@suse.com>
Cc: gor@linux.ibm.com, jpoimboe@redhat.com, jikos@kernel.org,
mbenes@suse.cz, 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, paulmck@kernel.org
Subject: Re: [RFC][PATCH 7/7] livepatch,context_tracking: Avoid disturbing NOHZ_FULL tasks
Date: Thu, 23 Sep 2021 15:28:56 +0200 [thread overview]
Message-ID: <YUyBGJGCgrR56C7r@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <YUx9yNfgm4nnd23y@alley>
On Thu, Sep 23, 2021 at 03:14:48PM +0200, Petr Mladek wrote:
> IMHO, this is not safe:
>
> CPU0 CPU1
>
> klp_check_task(A)
> if (context_tracking_state_cpu(task_cpu(task)) == CONTEXT_USER)
> goto complete;
>
> clear_tsk_thread_flag(task, TIF_PATCH_PENDING);
>
> # task switching to kernel space
> klp_update_patch_state(A)
> if (test_and_clear_tsk_thread_flag(task, TIF_PATCH_PENDING))
> //false
>
> # calling kernel code with old task->patch_state
>
> task->patch_state = klp_target_state;
>
> BANG: CPU0 sets task->patch_state when task A is already running
> kernel code on CPU1.
Why is that a problem? That is, who actually cares about
task->patch_state ? I was under the impression that state was purely for
klp itself, to track which task has observed the new state.
next prev parent reply other threads:[~2021-09-23 13:32 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
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 [this message]
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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