From: Stephen Hemminger <shemminger@vyatta.com>
To: Daniel Walker <dwalker@codeaurora.org>
Cc: "Harford, Jim" <c_jharfo@quicinc.com>,
"David S. Miller" <davem@davemloft.net>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"Smith, Alan" <agsmith@quicinc.com>
Subject: Re: [PATCH] net: Fix race condition on receive path.
Date: Fri, 5 Mar 2010 15:48:12 -0800 [thread overview]
Message-ID: <20100305154812.55a59038@nehalam> (raw)
In-Reply-To: <1267832667.30393.16.camel@c-dwalke-linux.qualcomm.com>
On Fri, 05 Mar 2010 15:44:27 -0800
Daniel Walker <dwalker@codeaurora.org> wrote:
> On Fri, 2010-03-05 at 15:41 -0800, Harford, Jim wrote:
> > It appears that this patch is no longer necessary. It was made against 2.6.29, but I see that more recent kernel versions don't have the problem code. For a more detailed explanation, see below. All code references are in routine process_backlog(), file net/core/dev.c.
> >
> > In kernel version 2.6.27.45, __napi_complete() is invoked BEFORE interrupts are re-enabled. Thus, the receive queue status is cleaned up before another interrupt (due to a receive packet) can occur. This is good design.
> >
> > In kernel version 2.6.29, git commit ID 303c6a025 inverts this ordering. Routine napi_complete() is invoked AFTER interrupts are re-enabled. We observed interrupts taken after interrupts were re-enabled, but before napi_complete cleaned up the receive queue. This would then shut down the processing of subsequent received packets.
> >
> > In kernel versions 2.6.30.10 and later, the sequence of operations is identical to 2.6.27.45, so there is no problem.
> >
> > Jim Harford
> > Qualcomm Innovation Center
>
> Ok, I guess we can ignore this one then.
>
> Daniel
>
It was fixed by:
commit 8f1ead2d1a626ed0c85b3d2c2046a49081d5933f
Author: Herbert Xu <herbert@gondor.apana.org.au>
Date: Thu Mar 26 00:59:10 2009 -0700
GRO: Disable GRO on legacy netif_rx path
When I fixed the GRO crash in the legacy receive path I used
napi_complete to replace __napi_complete. Unfortunately they're
not the same when NETPOLL is enabled, which may result in us
not calling __napi_complete at all.
What's more, we really do need to keep the __napi_complete call
within the IRQ-off section since in theory an IRQ can occur in
between and fill up the backlog to the maximum, causing us to
lock up.
Since we can't seem to find a fix that works properly right now,
this patch reverts all the GRO support from the netif_rx path.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
prev parent reply other threads:[~2010-03-05 23:48 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-05 19:34 [PATCH] net: Fix race condition on receive path Daniel Walker
2010-03-05 21:21 ` Stephen Hemminger
2010-03-05 23:41 ` Harford, Jim
2010-03-05 23:44 ` Daniel Walker
2010-03-05 23:48 ` Stephen Hemminger [this message]
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