linux-kernel - Re: [PATCH v5 2/7] scsi: libsas: shut down the PHY if events reached the threshold

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Message-ID: <c1accdc7-00a7-06a3-5531-ae64ef797cd2@suse.de>
Date:   Fri, 15 Dec 2017 13:18:32 +0100
From:   Hannes Reinecke <hare@...e.de>
To:     Jason Yan <yanaijie@...wei.com>, martin.petersen@...cle.com,
        jejb@...ux.vnet.ibm.com
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        john.garry@...wei.com, zhaohongjiang@...wei.com, hare@...e.com,
        dan.j.williams@...el.com, jthumshirn@...e.de,
        Raj.Dinesh@...rosemi.com, hch@....de, huangdaode@...ilicon.com,
        chenxiang66@...ilicon.com, xiyou.wangcong@...il.com,
        Ewan Milne <emilne@...hat.com>, Tomas Henzl <thenzl@...hat.com>
Subject: Re: [PATCH v5 2/7] scsi: libsas: shut down the PHY if events reached
 the threshold

On 12/08/2017 10:42 AM, Jason Yan wrote:
> If the PHY burst too many events, we will alloc a lot of events for the
> worker. This may leads to memory exhaustion.
> 
> Dan Williams suggested to shut down the PHY if the events reached the
> threshold, because in this case the PHY may have gone into some
> erroneous state. Users can re-enable the PHY by sysfs if they want.
> 
> We cannot use the fixed memory pool because if we run out of events, the
> shut down event and loss of signal event will lost too. The events still
> need to be allocated and processed in this case.
> 
> Suggested-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Jason Yan <yanaijie@...wei.com>
> CC: John Garry <john.garry@...wei.com>
> CC: Johannes Thumshirn <jthumshirn@...e.de>
> CC: Ewan Milne <emilne@...hat.com>
> CC: Christoph Hellwig <hch@....de>
> CC: Tomas Henzl <thenzl@...hat.com>
> ---
>  drivers/scsi/libsas/sas_init.c | 33 ++++++++++++++++++++++++++++++++-
>  drivers/scsi/libsas/sas_phy.c  | 27 ++++++++++++++++++++++++++-
>  include/scsi/libsas.h          |  6 ++++++
>  3 files changed, 64 insertions(+), 2 deletions(-)
> 
Well, this still looks a bit error prone; what if the system runs out of
memory before the pool is exhausted?
(Also a threshold of 1024 events is a bit arbitrary; one might want to
adjust that).

Couldn't you allocate two static events always (for shutdown and signal
loss), and then use a fixed pool?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@...e.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)