720f1de402
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>
Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.