netdev - Re: [PATCH net v2] pktgen: do not sleep with the thread lock held.

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Date:   Thu, 06 Jun 2019 11:32:27 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     pabeni@...hat.com
Cc:     netdev@...r.kernel.org, mcroce@...hat.com
Subject: Re: [PATCH net v2] pktgen: do not sleep with the thread lock held.

From: Paolo Abeni <pabeni@...hat.com>
Date: Thu,  6 Jun 2019 15:45:03 +0200

> Currently, the process issuing a "start" command on the pktgen procfs
> interface, acquires the pktgen thread lock and never release it, until
> all pktgen threads are completed. The above can blocks indefinitely any
> other pktgen command and any (even unrelated) netdevice removal - as
> the pktgen netdev notifier acquires the same lock.
> 
> The issue is demonstrated by the following script, reported by Matteo:
> 
> ip -b - <<'EOF'
> 	link add type dummy
> 	link add type veth
> 	link set dummy0 up
> EOF
> modprobe pktgen
> echo reset >/proc/net/pktgen/pgctrl
> {
> 	echo rem_device_all
> 	echo add_device dummy0
> } >/proc/net/pktgen/kpktgend_0
> echo count 0 >/proc/net/pktgen/dummy0
> echo start >/proc/net/pktgen/pgctrl &
> sleep 1
> rmmod veth
> 
> Fix the above releasing the thread lock around the sleep call.
> 
> Additionally we must prevent racing with forcefull rmmod - as the
> thread lock no more protects from them. Instead, acquire a self-reference
> before waiting for any thread. As a side effect, running
> 
> rmmod pktgen
> 
> while some thread is running now fails with "module in use" error,
> before this patch such command hanged indefinitely.
> 
> Note: the issue predates the commit reported in the fixes tag, but
> this fix can't be applied before the mentioned commit.
> 
> v1 -> v2:
>  - no need to check for thread existence after flipping the lock,
>    pktgen threads are freed only at net exit time
>  -
> 
> Fixes: 6146e6a43b35 ("[PKTGEN]: Removes thread_{un,}lock() macros.")
> Reported-and-tested-by: Matteo Croce <mcroce@...hat.com>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

This looks a lot simpler.

Applied and queued up for -stable, thanks.