On Tue, Jun 18, 2024 at 10:02:10AM -0700, Jakub Kicinski wrote: > On Tue, 18 Jun 2024 09:42:35 -0700 Paul E. McKenney wrote: > > > FTR, with mptcp self-tests we hit a few kmemleak false positive on RCU > > > freed pointers, that where addressed by to this patch: > > > > > > commit 5f98fd034ca6fd1ab8c91a3488968a0e9caaabf6 > > > Author: Catalin Marinas <catalin.marinas@xxxxxxx> > > > Date: Sat Sep 30 17:46:56 2023 +0000 > > > > > > rcu: kmemleak: Ignore kmemleak false positives when RCU-freeing objects > > > > > > I'm wondering if this is hitting something similar? Possibly due to > > > lazy RCU callbacks invoked after MSECS_MIN_AGE??? > > Dmitry mentioned this commit, too, but we use the same config for MPTCP > tests, and while we repro TCP AO failures quite frequently, mptcp > doesn't seem to have failed once. > > > Fun! ;-) > > > > This commit handles memory passed to kfree_rcu() and friends, but > > not memory passed to call_rcu() and friends. Of course, call_rcu() > > does not necessarily know the full extent of the memory passed to it, > > for example, if passed a linked list, call_rcu() will know only about > > the head of that list. > > > > There are similar challenges with synchronize_rcu() and friends. > > To be clear I think Dmitry was suspecting kfree_rcu(), he mentioned > call_rcu() as something he was expecting to have a similar issue but > it in fact appeared immune. > In the kfree_rcu() there is "an ignore" injection: <snip> /* * The kvfree_rcu() caller considers the pointer freed at this point * and likely removes any references to it. Since the actual slab * freeing (and kmemleak_free()) is deferred, tell kmemleak to ignore * this object (no scanning or false positives reporting). */ kmemleak_ignore(ptr); // Set timer to drain after KFREE_DRAIN_JIFFIES. if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING) schedule_delayed_monitor_work(krcp); <snip> -- Uladzislau Rezki
