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Date: Wed, 17 Jan 2024 12:31:33 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Chen Zhongjin <chenzhongjin@huawei.com>
Cc: <linux-kernel@vger.kernel.org>, <linux-trace-kernel@vger.kernel.org>,
 <yangjihong1@huawei.com>, <naveen.n.rao@linux.ibm.com>,
 <anil.s.keshavamurthy@intel.com>, <davem@davemloft.net>,
 <paulmck@kernel.org>, <mhiramat@kernel.org>, <tglx@linutronix.de>,
 <peterz@infradead.org>, <pmladek@suse.com>, <dianders@chromium.org>,
 <npiggin@gmail.com>, <mpe@ellerman.id.au>, <jkl820.git@gmail.com>,
 <juerg.haefliger@canonical.com>, <rick.p.edgecombe@intel.com>,
 <eric.devolder@oracle.com>, <mic@digikod.net>
Subject: Re: [PATCH] kprobes: Use synchronize_rcu_tasks_rude in
 kprobe_optimizer
Message-Id: <20240117123133.2e40438936167e6a4aec8b16@linux-foundation.org>
In-Reply-To: <20240117061636.288412-1-chenzhongjin@huawei.com>
References: <20240117061636.288412-1-chenzhongjin@huawei.com>
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On Wed, 17 Jan 2024 06:16:36 +0000 Chen Zhongjin <chenzhongjin@huawei.com> wrote:

> There is a deadlock scenario in kprobe_optimizer():
> 
> pid A				pid B			pid C
> kprobe_optimizer()		do_exit()		perf_kprobe_init()
> mutex_lock(&kprobe_mutex)	exit_tasks_rcu_start()	mutex_lock(&kprobe_mutex)
> synchronize_rcu_tasks()		zap_pid_ns_processes()	// waiting kprobe_mutex
> // waiting tasks_rcu_exit_srcu	kernel_wait4()
> 				// waiting pid C exit
> 
> To avoid this deadlock loop, use synchronize_rcu_tasks_rude() in kprobe_optimizer()
> rather than synchronize_rcu_tasks(). synchronize_rcu_tasks_rude() can also promise
> that all preempted tasks have scheduled, but it will not wait tasks_rcu_exit_srcu.
> 
> Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>

Thanks.  Should we backport this fix into earlier kernels?  If so, are
we able to identify a suitable Fixes: target?