linux-kernel - RE: [Linuxarm] Re: [PATCH for-next 00/32] spin lock usage optimization for SCSI drivers

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Date:   Wed, 10 Feb 2021 15:16:03 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>
cc:     tanxiaofei <tanxiaofei@...wei.com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "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>,
        "linuxarm@...neuler.org" <linuxarm@...neuler.org>,
        "linux-m68k@...r.kernel.org" <linux-m68k@...r.kernel.org>
Subject: RE: [Linuxarm]  Re: [PATCH for-next 00/32] spin lock usage optimization
 for SCSI drivers

On Tue, 9 Feb 2021, Song Bao Hua (Barry Song) wrote:

> > > sonic_interrupt() uses an irq lock within an interrupt handler to 
> > > avoid issues relating to this. This kind of locking may be needed in 
> > > the drivers you are trying to patch. Or it might not. Apparently, 
> > > no-one has looked.
> 
> Is the comment in sonic_interrupt() outdated according to this:
> m68k: irq: Remove IRQF_DISABLED
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=77a4279
> http://lkml.iu.edu/hypermail/linux/kernel/1109.2/01687.html
> 

The removal of IRQF_DISABLED isn't relevant to this driver. Commit 
77a42796786c ("m68k: Remove deprecated IRQF_DISABLED") did not disable 
interrupts, it just removed some code to enable them.

The code and comments in sonic_interrupt() are correct. You can confirm 
this for yourself quite easily using QEMU and a cross-compiler.

> and this:
> genirq: Warn when handler enables interrupts
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b738a50a
> 
> wouldn't genirq report a warning on m68k?
> 

There is no warning from m68k builds. That's because arch_irqs_disabled() 
returns true when the IPL is non-zero.

> > 
> > Thanks
> > Barry
> 
> Thanks
> Barry
> 
>