netdev - Re: [TEST] TCP MD5 vs kmemleak

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Date: Tue, 18 Jun 2024 10:02:10 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Paolo Abeni <pabeni@...hat.com>, Dmitry Safonov <0x7f454c46@...il.com>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>, rcu@...r.kernel.org
Subject: Re: [TEST] TCP MD5 vs kmemleak

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@....com>
> > 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.