linux-kernel - Re: [PATCH] scsi_lib: increase {host|target|device}

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Message-ID: <CADAEsF8OySXKpqBmN-Vi+8md=RpHAyUghO99UnrwJRdD72yWCQ@mail.gmail.com>
Date:   Fri, 2 Mar 2018 12:56:26 +0800
From:   Ganesh Mahendran <opensource.ganesh@...il.com>
To:     Bart Van Assche <Bart.VanAssche@....com>
Cc:     "jejb@...ux.vnet.ibm.com" <jejb@...ux.vnet.ibm.com>,
        "hch@....de" <hch@....de>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] scsi_lib: increase {host|target|device}_busy count after
 dispatch cmd

Hi, Bart:

2018-03-02 7:11 GMT+08:00 Bart Van Assche <Bart.VanAssche@....com>:
> On Mon, 2017-06-05 at 17:37 +0800, Ganesh Mahendran wrote:
>> In android system, when there are lots of threads running. Thread A
>> holding *host_busy* count is easily to be preempted, and if at the
>> same time, thread B set *host_blocked*, then all other threads will
>> be io blocked.
>
> Hello Ganesh,
>
> Have you considered to insert preempt_disable() and preempt_enable() calls
> where necessary to achieve the same effect? I think that would result in a
> much less intrusive patch.

Yes, preempt_disable()preempt_enable will also achieve the same effect.
But I just think preempt_disable()preempt_enable may be a little heavy for
this problem which can be fixed by increaseing {host|target|device}_busy count
after dispatch cmd.

Thanks.

>
> Thanks,
>
> Bart.
>
>