linux-kernel - Re: [PATCH] MIPS: Remove noreturn attribute for die()

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Date:   Wed, 9 Aug 2023 17:30:09 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     "Maciej W. Rozycki" <macro@...am.me.uk>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH] MIPS: Remove noreturn attribute for die()

On 08/08/2023 10:54 PM, Maciej W. Rozycki wrote:
> On Tue, 1 Aug 2023, Tiezhu Yang wrote:
>
>> If notify_die() returns NOTIFY_STOP, there is no need to call
>> make_task_dead(), we can remove noreturn attribute for die(),
>> this is similar with arm64, riscv and csky.
>
>  So you want to keep a task alive that has caused a kernel oops in the
> process context in this case, right?  What purpose would it be for and
> what condition causes `notify_die' to return NOTIFY_STOP?  IOW why is
> there no need to call `make_task_dead' in this case?
>
>   Maciej
>

I did some research, hope it is useful.

There is a related description in Documentation/input/notifier.rst:

   For each kind of event but the last, the callback may return
   NOTIFY_STOP in order to "eat" the event: the notify loop is
   stopped and the keyboard event is dropped.

In commit 748f2edb5271 ("x86 NMI: better support for debuggers"), it said:

   If the notify is handled with a NOTIFY_STOP return, the
   system is given a new lease on life.

In commit 004429956b48 ("handle recursive calls to bust_spinlocks()"),
it said:

   However, at least on i386 die() has been capable of returning
   (and on other architectures this should really be that way, too)
   when notify_die() returns NOTIFY_STOP.

In commit 22f5991c85de ("x86-64: honor notify_die() returning NOTIFY_STOP"),
it said:

   This requires making die() return a value, making its callers honor
   this (and be prepared that it may return)

In commit 620de2f5dc69 ("[IA64] honor notify_die() returning NOTIFY_STOP"),
it said:

   This requires making die() and die_if_kernel() return a value,
   and their callers to honor this (and be prepared that it returns).

Thanks,
Tiezhu