linux-kernel - Re: kernel BUG at drivers/scsi/aic7xxx/aic79xx

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Date:	Sun, 09 Mar 2008 10:59:30 -0500
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Michael Tokarev <mjt@....msk.ru>
Cc:	FUJITA Tomonori <tomof@....org>, linux-kernel@...r.kernel.org,
	linux-scsi@...r.kernel.org, fujita.tomonori@....ntt.co.jp
Subject: Re: kernel BUG at drivers/scsi/aic7xxx/aic79xx_osm.c:1490!

On Sun, 2008-03-09 at 18:42 +0300, Michael Tokarev wrote:
> Michael Tokarev wrote:
> > James Bottomley wrote:
> >> On Sun, 2008-03-09 at 21:29 +0900, FUJITA Tomonori wrote:
> >>> On Sun, 09 Mar 2008 14:23:13 +0300
> >>> Michael Tokarev <mjt@....msk.ru> wrote:
> >>>
> >>>> Just got quite.. bad situation on a production server
> >>>> here.  The machine locked up hard several times in a
> >>>> row (required hard reboot).  So I finally enabled watchdog
> >>>> subsystem which helped.
> >>>>
> >>>> Now I see the following (over netconsole):
> >>>>
> >>>> DMA: Out of SW-IOMMU space for 65536 bytes at device 0000:08:07.0
> >>>> ------------[ cut here ]------------
> >>>> kernel BUG at drivers/scsi/aic7xxx/aic79xx_osm.c:1490!
> >>> Seems that you was out of swiommu space (and aic79xx can't handle it
> >>> though it should). This happened because:
> >>>
> >>> a) you produced more I/Os than swiommu can handle.
> >>>
> >>> b) swiommu space leaks due to bugs.
> >>>
> >>> If you hit this problem due to a), the following boot option might
> >>> help:
> >>>
> >>> swiotlb=65536
> > 
> > Running with this parameter now - no lockups so far.
> > 
> >> Actually, it's worse than this.  The aic79xx is a fully 64 bit capable
> >> PCI card, it shouldn't be using the iommu at all.  However, it has three
> >> DMA modes:  64 bit, 39 bit and 32 bit; with a corresponding resource
> >> cost increasing with the number of bits.  It employs special APIs to
> >> size the masks according to the memory, in aic79xx_osm_pci.c:
> > []
> >> Could you firstly tell me how much memory you have, and secondly
> >> instrument this code with the patch below to see if we can work out what
> >> it's doing?
> > 
> > The memory map is below (6Gb total).  The patch - kernel is being compiled
> > right now.
> 
> And here's the result (without swiotlb=65536):
> 
> DEBUG: RETURNED REQUIRED MASK ffffffff
> DEBUG: SET 32 BIT ADDRESSING
> 
> (which doesn't look like a good thing, provided this
> machine has 6Gb of memory...)

That's the root cause then.

There's a bug in the generic implementation of dma_get_required_mask(),
a fix for which is below, if you could try it (still with the debugging
patches to make sure it's working).

James

---

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index efaf282..911ec60 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -648,7 +648,7 @@ u64 dma_get_required_mask(struct device *dev)
 		high_totalram += high_totalram - 1;
 		mask = (((u64)high_totalram) << 32) + 0xffffffff;
 	}
-	return mask & *dev->dma_mask;
+	return mask;
 }
 EXPORT_SYMBOL_GPL(dma_get_required_mask);
 #endif




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