lkml.org 
[lkml]   [2009]   [Oct]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch] Staging: hv: Fix vmbus load hang caused by wrong data packing
On Mon, Oct 12, 2009 at 08:10:40PM +0000, Hank Janssen wrote:
>
> >Odd quoting style :(
>
> We like to keep things lively :)
>
> >> Based on our testing, the #pragma pack(push,1) can pack the data
> >> correctly for the HyperV to use, but __attribute__((packed)) couldn't
> >> do this right.
> >
> >Why? What does gcc generate differently? This should be identical.
>
> It should, but in practice in this case it does not seem to behave the same
> Way.

Can you figure out why? What is the output of gcc for both ways?

Can you show what is fixed by this change?

Also note that #pragma packed is not supported by older versions of gcc,
so I don't think that it would work at all on some compiler versions
that are still legal to use for the kernel. But I'm not quite sure when
it was added, so I might be wrong.

> >Ideally, we don't deal with packed structures at all, but with offsets
> >in memory and pick out the proper fields and put them into new
> >structures if you want to use them that way. How hard would that be to
> >do here instead?
>
> It is something that I want to look at in the future. Our primary focus
> Is to get the bug fixed. We cannot do the offset way in the time we
> Have before 2.6.32 closes and still be comfortable we have gone through
> The extensive testing cycle we do on our side.

I can't take this patch until I see what the root problem is here,
sorry.

> >I still want to figure out what the real difference here is. Especially
> >as I removed a lot of the #pragma pack(push,1) lines from the hv code.
> >If it really is different, all of those patches should be reverted,
> >right?
>
> Not sure yet if they need to be reverted, after we fixed this bug last week
> We are getting another one, it was masked by the one we just fixed.
> We are checking into that right now;
>
> BUG: unable to handle kernel NULL pointer dereference at (null)

What is the rest of the oops message? That's pretty hard to determine
anything from :)

thanks,

greg k-h


\
 
 \ /
  Last update: 2009-10-12 22:33    [W:0.054 / U:0.576 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site