Alexander Duyck [off-list ref] :

On 11/13/2014 01:30 PM, Francois Romieu wrote:

quoted

Alexander Duyck [off-list ref] :
[...]

quoted

In addition the r8169 uses a rmb() however I believe it is placed incorrectly
as I assume it supposed to be ordering descriptor reads after the check for
ownership.

Not exactly. It's a barrier against compiler optimization from 2004.
It should not matter.

Okay.  Do you recall the kind of problem it was you were seeing ?

Mildly, I had to grep the local archives.

The relevant code used to be included in the irq handler at that time
(napi support for this driver took place in may 2004). One did not want
a runaway loop in the Tx reaper.

Compiler optimization was suggested by Manfred Spraul in the thread below:
http://marc.info/?l=linux-kernel&m=108096868119004

The origin of the rmb() for the Intel drivers was a PowerPC issue in
which it was fetching the length of a buffer before it checked the DD
bit (equivalent of DescOwn).  I'm wondering if the issue you were seeing
was something similar where it had reordered reads in the descriptor to
cause that type of result.

The problem was only reported on Intel 32 bit + slackware + gcc 3.2.3.

Adam Nielsen - Cc: added - did not return for this bug.

-- 
Ueimor