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From: Przemek Socha <soprwa@gmail.com>
To: Ming Lei <ming.lei@redhat.com>
Reply-To: soprwa@gmail.com
Cc: Christoph Hellwig <hch@lst.de>, Patrick Steinhardt <ps@pks.im>,
        Bart Van Assche <Bart.VanAssche@wdc.com>,
        Tomas Janousek <tomi@nomi.cz>,
        Alan Stern <stern@rowland.harvard.edu>, stable@vger.kernel.org
Subject: Re: [PATCH] block: really disable runtime-pm for blk-mq
Date: Mon, 30 Jul 2018 17:14:03 +0200
Message-ID: <2191598.hWjFyhWQyz@eclipse>
In-Reply-To: <20180730120219.24164-1-ming.lei@redhat.com>
References: <20180730120219.24164-1-ming.lei@redhat.com>
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Dnia poniedzia=C5=82ek, 30 lipca 2018 14:02:19 CEST piszesz:
> Runtime PM isn't ready for blk-mq yet, and commit 765e40b675a9 ("block:
> disable runtime-pm for blk-mq") tried to disable it. Unfortunately,
> it can't take effect in that way since user space still can switch
> it on via 'echo auto > /sys/block/sdN/device/power/control'.
>=20
> This patch disables runtime-pm for blk-mq really by pm_runtime_disable()
> and fixes all kinds of PM related kernel crash.
>=20
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Patrick Steinhardt <ps@pks.im>
> Cc: Bart Van Assche <Bart.VanAssche@wdc.com>
> Cc: Tomas Janousek <tomi@nomi.cz>
> Cc: Przemek Socha <soprwa@gmail.com>
> Cc: Alan Stern <stern@rowland.harvard.edu>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  block/blk-core.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>=20
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 03a4ea93a5f3..090b782df129 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -3769,9 +3769,11 @@ EXPORT_SYMBOL(blk_finish_plug);
>   */
>  void blk_pm_runtime_init(struct request_queue *q, struct device *dev)
>  {
> -	/* not support for RQF_PM and ->rpm_status in blk-mq yet */
> -	if (q->mq_ops)
> +	/* Don't enable runtime PM for blk-mq until it is ready */
> +	if (q->mq_ops) {
> +		pm_runtime_disable(dev);
>  		return;
> +	}
>=20
>  	q->dev =3D dev;
>  	q->rpm_status =3D RPM_ACTIVE;

This patch works perfectly with SATA ssd. I have checked "resume" with all=
=20
schedulers and with kernel command line "scsi_mod.use_blk_mq=3D1" option  (=
bfq,=20
kyber, deadline-mq). There is no more kernel oops with NULL pointer=20
dereference, and machine can resume successfully. When this patch will get =
to=20
stable tree i will close that bug report : https://bugzilla.kernel.org/
show_bug.cgi?id=3D200435.

Thank you very much,
Przemek.