From: David Miller <davem@davemloft.net>
To: pabeni@redhat.com
Cc: netdev@vger.kernel.org, mcroce@redhat.com
Subject: Re: [PATCH net v2] pktgen: do not sleep with the thread lock held.
Date: Thu, 06 Jun 2019 11:32:27 -0700 (PDT) [thread overview]
Message-ID: <20190606.113227.492005574306351502.davem@davemloft.net> (raw)
In-Reply-To: <011e3de13ea55a66d55024b5555cefd9dd8ec4c3.1559828069.git.pabeni@redhat.com>
From: Paolo Abeni <pabeni@redhat.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@redhat.com>
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This looks a lot simpler.
Applied and queued up for -stable, thanks.
prev parent reply other threads:[~2019-06-06 18:32 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-06 13:45 [PATCH net v2] pktgen: do not sleep with the thread lock held Paolo Abeni
2019-06-06 18:32 ` David Miller [this message]
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