linux-kernel - Re: [Fdutils] DMA cache consistency bug introduced in 2.6.28

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Date:	Wed, 23 Dec 2009 08:49:38 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Mark Hounschell <markh@...pro.net>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	"dmarkh@....rr.com" <dmarkh@....rr.com>,
	Alain Knaff <alain@...ff.lu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"fdutils@...tils.linux.lu" <fdutils@...tils.linux.lu>,
	"Li, Shaohua" <shaohua.li@...el.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [Fdutils] DMA cache consistency bug introduced in 2.6.28



On Wed, 23 Dec 2009, Andi Kleen wrote:
> 
> I suspect it's a system where the APIC timer stops in deeper idle
> states and it supports them. In this case CPU #0 does timer broadcasts
> when needed to wake the other CPUs up from deep C, but for that it has
> to run with HPET. At least the other ones can still enjoy the LAPIC
> timer.

Ahh, ok, that makes sense. I was assuming the broadcast timer would act in 
that capacity, but..

> This might suggest that Mark's floppy controller doesn't like
> deep C? Mark, did you try booting with processor.max_cstate=1
> and HPET enabled?

We have indeed had historical issues with floppy and sleep states before. 

I do note another issue, though - the floppy driver itself seems totally 
broken when it comes to using interleaved sectors. Alain, that "place 
logical sectors" code is simply _broken_ - the "while" kicks in only if 
the first sector we test is busy _and_ we were at the last sector so that 
we increment past F_SECT_PER_TRACK.

So shouldn't that sector layout be something like the appended?

		Linus
---
 drivers/block/floppy.c |    7 ++-----
 1 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 3266b4f..9c9148c 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -2237,13 +2237,10 @@ static void setup_format_params(int track)
 	for (count = 1; count <= F_SECT_PER_TRACK; ++count) {
 		here[n].sect = count;
 		n = (n + il) % F_SECT_PER_TRACK;
-		if (here[n].sect) {	/* sector busy, find next free sector */
+		while (here[n].sect) {	/* sector busy, find next free sector */
 			++n;
-			if (n >= F_SECT_PER_TRACK) {
+			if (n >= F_SECT_PER_TRACK)
 				n -= F_SECT_PER_TRACK;
-				while (here[n].sect)
-					++n;
-			}
 		}
 	}
 	if (_floppy->stretch & FD_SECTBASEMASK) {
--
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