lkml.org 
[lkml]   [2007]   [Jul]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch] revert: [NET]: Fix races in net_rx_action vs netpoll


On Mon, 16 Jul 2007, David Miller wrote:
>
> Well, let's figure out why before we revert because it
> is attempting to fix a legitimate bug.

I'm reverting it. I don't think there is any excuse for not reverting
something that provably breaks somebody's machine. I don't want this to be
on the regression list - if you figure out why it broke, you can always
just resubmit a fixed patch.

Keeping a known broken patch around just because you want to figure out
why it's broken seems pointless.

Just looking at the patch I see two options:

- The change seems to always set the LIST_FROZEN bit when calling
->poll(), and at least on e1000, the NAPI poll() routine ends up doing
that netif_rx_complete(), so we're *guaranteed* to always take the
early exit and not do anything.

Looks fundamentally broken to me, and not worth saving. But maybe I'm
missing something (and it doesn't really seem to explain the write
timeout per se).

- The early return from netif_rx_complete() ends up meaning that an
edge-triggered interrupt isn't handled properly, and will this never
happen again, since it never goes away.

With MSI, edge-triggered interrupts are making a comeback in a big way,
and yeah, e1000 is one of the drivers that do MSI. Ingo might want to
confirm whether it's actually enabled for him, and whether turning it
off might hide the problem, but if that's it, then the whole patch is
fundamentally broken, and not worth saving.

but in either case (or, indeed, even if I didn't see any problem at all),
I think reverting a patch that isn't needed is _always_ the right choice.

If we don't know what caused a problem in the first place, or if the fix
is known to be required for something else and reverting it would cause
*another* regression, it would be another issue. But as it is, reverting
it would seem to unquestionably get rid of a regression, and is thus a
no-brainer.

No?

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

\
 
 \ /
  Last update: 2007-07-16 23:45    [W:0.121 / U:1.372 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site