On Thu, Jul 10, 2025 at 07:06:09AM -0700, Breno Leitao wrote: > Hello Boqun, > > On Tue, Jun 24, 2025 at 08:11:01PM -0700, Boqun Feng wrote: > > Erik Lundgren and Breno Leitao reported [1] a case where > > lockdep_unregister_key() can be called from time critical code pathes > > where rntl_lock() may be held. And the synchronize_rcu() in it can slow > > down operations such as using tc to replace a qdisc in a network device. > > > > In fact the synchronize_rcu() in lockdep_unregister_key() is to wait for > > all is_dynamic_key() callers to finish so that removing a key from the > > key hashlist, and we can use shazptr to protect the hashlist as well. > > > > Compared to the proposed solution which replaces synchronize_rcu() with > > synchronize_rcu_expedited(), using shazptr here can achieve the > > same/better synchronization time without the need to send IPI. Hence use > > shazptr here. > > > > Reported-by: Erik Lundgren <elundg...@meta.com> > > Reported-by: Breno Leitao <lei...@debian.org> > > Link: > > https://lore.kernel.org/all/20250321-lockdep-v1-1-78b732d19...@debian.org/ > > [1] > > Signed-off-by: Boqun Feng <boqun.f...@gmail.com> > > First of all, thanks for working to fix the origianl issue. I've been > able to test this in my host, and the gain is impressive. > > Before: > > # time /usr/sbin/tc qdisc replace dev eth0 root handle 0x1234: mq > real 0m13.195s > user 0m0.001s > sys 0m2.746s > > With your patch: > > # time /usr/sbin/tc qdisc replace dev eth0 root handle 0x1234: mq > real 0m0.135s > user 0m0.002s > sys 0m0.116s > > # time /usr/sbin/tc qdisc replace dev eth0 root handle 0x1: mq > real 0m0.127s > user 0m0.001s > sys 0m0.112s > > Please add the following to the series: > > Tested-by: Breno Leitao <lei...@debian.org>
Thanks! Will apply ;-) Regards, Boqun
