linux-kernel - Re: 答复: 答复: 答复: 答复: [PATCH] kdb: Fix the deadlock issue in KDB debugging.

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Message-ID: <20240313141745.GD202685@aspen.lan>
Date: Wed, 13 Mar 2024 14:17:45 +0000
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Liuye <liu.yeC@....com>
Cc: "jason.wessel@...driver.com" <jason.wessel@...driver.com>,
	"dianders@...omium.org" <dianders@...omium.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"jirislaby@...nel.org" <jirislaby@...nel.org>,
	"kgdb-bugreport@...ts.sourceforge.net" <kgdb-bugreport@...ts.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: Re: 答复: 答复: 答复: 答复: [PATCH] kdb: Fix the deadlock
 issue in KDB debugging.

On Wed, Mar 13, 2024 at 01:22:17AM +0000, Liuye wrote:
> >On Tue, Mar 12, 2024 at 10:04:54AM +0000, Liuye wrote:
> >> >On Tue, Mar 12, 2024 at 08:37:11AM +0000, Liuye wrote:
> >> >> I know that you said schedule_work is not NMI save, which is the
> >> >> first issue. Perhaps it can be fixed using irq_work_queue. But
> >> >> even if irq_work_queue is used to implement it, there will still
> >> >> be a deadlock problem because slave cpu1 still has not released
> >> >> the running queue lock of master CPU0.
> >> >
> >> >This doesn't sound right to me. Why do you think CPU1 won't
> >> >release the run queue lock?
> >>
> >> In this example, CPU1 is waiting for CPU0 to release
> >> dbg_slave_lock.
> >
> >That shouldn't be a problem. CPU0 will have released that lock by the
> >time the irq work is dispatched.
>
> Release dbg_slave_lock in CPU0. Before that, shcedule_work needs to be
> handled, and we are back to the previous issue.

Sorry but I still don't understand what problem you think can happen
here. What is wrong with calling schedule_work() from the IRQ work
handler?

Both irq_work_queue() and schedule_work() are calls to queue deferred
work. It does not matter when the work is queued (providing we are lock
safe). What matters is when the work is actually executed.

Please can you describe the problem you think exists based on when the
work is executed.


Daniel.