linux-kernel - Re: [PATCH v3 66/77] ncr5380: Fix soft lockups

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 23 Dec 2015 00:47:36 +1100 (AEDT)
From:	Finn Thain <fthain@...egraphics.com.au>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
cc:	"James E.J. Bottomley" <JBottomley@...n.com>,
	Michael Schmitz <schmitzmic@...il.com>,
	linux-m68k@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 66/77] ncr5380: Fix soft lockups


On Tue, 22 Dec 2015, One Thousand Gnomes wrote:

> On Tue, 22 Dec 2015 12:18:44 +1100 Finn Thain 
> <fthain@...egraphics.com.au> wrote:
> 
> > Because of the rudimentary design of the chip, it is necessary to poll 
> > the SCSI bus signals during PIO and this tends to hog the CPU. The 
> > driver will accept new commands while others execute, and this causes 
> > a soft lockup because the workqueue item will not terminate until the 
> > issue queue is emptied.
> > 
> > When exercising dmx3191d using sequential IO from dd, the driver is 
> > sent 512 KiB WRITE commands and 128 KiB READs. For a PIO transfer, the 
> > rate is is only about 300 KiB/s, so these are long-running commands. 
> > And although PDMA may run at several MiB/s, interrupts are disabled 
> > for the duration of the transfer.
> > 
> > Fix the unresponsiveness and soft lockup issues by calling 
> > cond_resched() after each command is completed and by limiting 
> > max_sectors for drivers that don't implement real DMA.
> 
> Is there a reason for not doing some limiting in the DMA case too. A 
> 512K write command even with DMA on a low end 68K box introduces a 
> second of latency before another I/O can be scheduled ?

The DMA case is the atari_scsi case. I'd like to think that atari_scsi 
would have only the latency issues that might be expected from any SCSI-2 
host adapter driver.

Unlike PDMA, interrupts are not disabled for these DMA transfers. Note 
that this patch isn't really relevant to DMA, because the main loop 
iterates only when done == 0, that is, !hostdata->dmalen.

-- 

> 
> Alan

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/