0e4be9e57e
The combination of aca_free_rcu, introduced in commit2384d02520("net/ipv6: Add anycast addresses to a global hashtable"), and fib6_info_destroy_rcu, introduced in commit9b0a8da8c4("net/ipv6: respect rcu grace period before freeing fib6_info"), can result in an extra rcu grace period being needed when deleting an interface, with the result that netdev_wait_allrefs ends up hitting the msleep(250), which is considerably longer than the required grace period. This can result in long delays when deleting a large number of interfaces, and it can be observed with this script: ns=dummy-ns NIFS=100 ip netns add $ns ip netns exec $ns ip link set lo up ip netns exec $ns sysctl net.ipv6.conf.default.disable_ipv6=0 ip netns exec $ns sysctl net.ipv6.conf.default.forwarding=1 for ((i=0; i<$NIFS; i++)) do if=eth$i ip netns exec $ns ip link add $if type dummy ip netns exec $ns ip link set $if up ip netns exec $ns ip -6 addr add 2021:$i::1/120 dev $if done for ((i=0; i<$NIFS; i++)) do if=eth$i ip netns exec $ns ip link del $if done ip netns del $ns Instead of using a fixed msleep(250), this patch tries an extra rcu_barrier() followed by an exponential backoff. Time with this patch on a 5.4 kernel: real 0m7.704s user 0m0.385s sys 0m1.230s Time without this patch: real 0m31.522s user 0m0.438s sys 0m1.156s v2: use exponential backoff instead of trying to wake up netdev_wait_allrefs. v3: preserve reverse christmas tree ordering of local variables v4: try an extra rcu_barrier before the backoff, plus some cosmetic changes. Signed-off-by: Francesco Ruggeri <fruggeri@arista.com> Reviewed-by: Eric Dumazet <edumazet@google.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.