linux-kernel - Re: [PATCH RESEND] rtsx_usb_ms: Use msleep

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Date:	Mon, 2 May 2016 13:56:34 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Oleksandr Natalenko <oleksandr@...alenko.name>
Cc:	Ben Hutchings <ben@...adent.org.uk>,
	Lee Jones <lee.jones@...aro.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	Roger Tseng <rogerable@...ltek.com>,
	linux-kernel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH RESEND] rtsx_usb_ms: Use msleep_interruptible() in
 polling loop

On Mon, 02 May 2016 23:17:41 +0300 Oleksandr Natalenko <oleksandr@...alenko.name> wrote:

> This patch has already been posted to LKML by Ben Hutchings ~6 months
> ago, but AFAIK no further action were performed. However, this patch
> really fixes weird loadavg with RTS5129 card reader, so I would wonder
> if this could be merged. AFAIK, it has been applied to some distros'
> kernels, e.g., Ubuntu.
> 
> Original Ben's message goes below.
> 
> rtsx_usb_ms creates a task that mostly sleeps, but tasks in
> uninterruptible sleep still contribute to the load average (for
> bug-compatibility with Unix).  A load average of ~1 on a system that
> should be idle is somewhat alarming.
> 
> Change the sleep to be interruptible, but still ignore signals.
> 
> A better fix might be to replace this loop with a delayed work item.
> 

hm.

> index 1105db2..645dede 100644
> --- a/drivers/memstick/host/rtsx_usb_ms.c
> +++ b/drivers/memstick/host/rtsx_usb_ms.c
> @@ -706,7 +706,8 @@ poll_again:
>   		if (host->eject)
>   			break;
> 
> -		msleep(1000);
> +		if (msleep_interruptible(1000))
> +			flush_signals(current);
>   	}
> 
>   	complete(&host->detect_ms_exit);

flush_signals() is a bit scary.  If this was a userspace task and it
had (say) SIGINT pending then it would be very rude for a device driver
to rub that out.

But this isn't a userspace task - it's a kthread.  So I don't *think*
it can get any signals anyway?

And looking at Oleg's 9e7c8f8c62c1e1cda203b it appears that
flush_signals() is for flushing signals of a userspace task, not a
kthread?  Despite the comment "Flush all pending signals for this
kthread".

Confused.  It's been a while since I looked at this stuff and people
have mucked with it.  Oleg, can you please sort me out?