Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Mark Tomlinson <Mark.Tomlinson@alliedtelesis.co.nz>
To:     Greg KH <gregkh@linuxfoundation.org>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RESEND] tty/sysrq: Do not call sync directly from
 sysrq_do_reset()
Thread-Topic: [PATCH RESEND] tty/sysrq: Do not call sync directly from
 sysrq_do_reset()
Thread-Index: AQHUhcqxsQOYM6dIbkaK+PjfzFnZzKVijaSAgACj7IA=
Date:   Tue, 27 Nov 2018 19:58:17 +0000
Message-ID: <6d069b48-da59-911b-19cc-cc24d3136c48@alliedtelesis.co.nz>
References: <20181126205723.14478-1-mark.tomlinson@alliedtelesis.co.nz>
 <20181127101135.GA15856@kroah.com>
In-Reply-To: <20181127101135.GA15856@kroah.com>
Accept-Language: en-NZ, en-US
Content-Language: en-US
x-ms-exchange-messagesentrepresentingtype: 1
x-ms-exchange-transport-fromentityheader: Hosted
x-originating-ip: [10.32.16.78]
Content-Type: text/plain; charset="Windows-1252"
Content-ID: <3E2C62F5D2440C419F1EED802E708020@atlnz.lc>
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 27/11/18 11:11 PM, Greg KH wrote:
> On Tue, Nov 27, 2018 at 09:57:23AM +1300, Mark Tomlinson wrote:
>> sysrq_do_reset() is called in softirq context, so it cannot call
>> sync() directly. Instead, call orderly_reboot(), which creates a work
>> item to run /sbin/reboot, or do emergency_sync and restart if the
>> command fails.
>>
>> Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
>> ---
>>   drivers/tty/sysrq.c | 3 +--
>>   1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
>> index ad1ee5d01b53..f2ca32c1ad7c 100644
>> --- a/drivers/tty/sysrq.c
>> +++ b/drivers/tty/sysrq.c
>> @@ -660,8 +660,7 @@ static void sysrq_do_reset(struct timer_list *t)
>>  =20
>>   	state->reset_requested =3D true;
>>  =20
>> -	ksys_sync();
>> -	kernel_restart(NULL);
>> +	orderly_reboot();
>=20
> Is this something new?  Why haven't we had reports of this failing in
> the past?  Or has something changed recently to cause this to now be
> needed?
>=20
> thanks,
>=20
> greg k-h
>=20

As far as I can tell, sysrq_do_reset() is only used when setting the=20
"keyset" property in "/chosen/linux,sysrq-reset-seq" (which is what I=20
want to do). No DTS file in the kernel tree sets this, so I don't know=20
if anyone else is using this. I am wondering whether it ever worked. A=20
reboot does occur after a kernel panic, so if the console is not=20
available, it may appear to have worked.

Pressing the standard 'sysrq' key followed by 'b'(reboot) instead calls=20
sysrq_handle_reboot(), which does not call sync at all, but=20
emergency_restart(). Also, the 's'(sync) key calls emergency_sync(),=20
which performs the sync via a work queue.=