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From: David Miller <>
Subject: Re: [PATCH net] ppp: fix xmit recursion detection on ppp channels
Date: Wed, 09 Aug 2017 04:07:06 +0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

From: Guillaume Nault <>
Date: Tue, 8 Aug 2017 11:43:24 +0200

> Commit e5dadc65f9e0 ("ppp: Fix false xmit recursion detect with two ppp
> devices") dropped the xmit_recursion counter incrementation in
> ppp_channel_push() and relied on ppp_xmit_process() for this task.
> But __ppp_channel_push() can also send packets directly (using the
> .start_xmit() channel callback), in which case the xmit_recursion
> counter isn't incremented anymore. If such packets get routed back to
> the parent ppp unit, ppp_xmit_process() won't notice the recursion and
> will call ppp_channel_push() on the same channel, effectively creating
> the deadlock situation that the xmit_recursion mechanism was supposed
> to prevent.
> This patch re-introduces the xmit_recursion counter incrementation in
> ppp_channel_push(). Since the xmit_recursion variable is now part of
> the parent ppp unit, incrementation is skipped if the channel doesn't
> have any. This is fine because only packets routed through the parent
> unit may enter the channel recursively.
> Finally, we have to ensure that pch->ppp is not going to be modified
> while executing ppp_channel_push(). Instead of taking this lock only
> while calling ppp_xmit_process(), we now have to hold it for the full
> ppp_channel_push() execution. This respects the ppp locks ordering
> which requires locking ->upl before ->downl.
> Fixes: e5dadc65f9e0 ("ppp: Fix false xmit recursion detect with two ppp devices")
> Signed-off-by: Guillaume Nault <>

Applied, thank you.

      parent reply	other threads:[~2017-08-09  4:07 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-08  9:43 [PATCH net] ppp: fix xmit recursion detection on ppp channels Guillaume Nault
2017-08-08 13:16 ` Gao Feng
2017-08-08 13:58   ` [PATCH " Guillaume Nault
2017-08-08 14:21     ` Gao Feng
2017-08-09  4:07 ` David Miller [this message]

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