Development discussion of WireGuard
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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Jakub Kicinski <kuba@kernel.org>,
	Julia Lawall <Julia.Lawall@inria.fr>,
	linux-block@vger.kernel.org, kernel-janitors@vger.kernel.org,
	bridge@lists.linux.dev, linux-trace-kernel@vger.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	kvm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	Nicholas Piggin <npiggin@gmail.com>,
	netdev@vger.kernel.org, wireguard@lists.zx2c4.com,
	linux-kernel@vger.kernel.org, ecryptfs@vger.kernel.org,
	Neil Brown <neilb@suse.de>, Olga Kornievskaia <kolga@netapp.com>,
	Dai Ngo <Dai.Ngo@oracle.com>, Tom Talpey <tom@talpey.com>,
	linux-nfs@vger.kernel.org, linux-can@vger.kernel.org,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
	Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH 00/14] replace call_rcu by kfree_rcu for simple kmem_cache_free callback
Date: Thu, 13 Jun 2024 16:11:52 +0200	[thread overview]
Message-ID: <Zmr-KPG9F6w-uzys@zx2c4.com> (raw)
In-Reply-To: <e06440e2-9121-4c92-8bf2-945977987052@paulmck-laptop>

On Thu, Jun 13, 2024 at 05:46:11AM -0700, Paul E. McKenney wrote:
> How about a kmem_cache_destroy_rcu() that marks that specified cache
> for destruction, and then a kmem_cache_destroy_barrier() that waits?
> 
> I took the liberty of adding your name to the Google document [1] and
> adding this section:

Cool, though no need to make me yellow!

> > But then, if that mechanism generally works, we don't really need a new
> > function and we can just go with the first option of making
> > kmem_cache_destroy() asynchronously wait. It'll wait, as you described,
> > but then we adjust the tail of every kfree_rcu batch freeing cycle to
> > check if there are _still_ any old outstanding kmem_cache_destroy()
> > requests. If so, then we can splat and keep the old debugging info we
> > currently have for finding memleaks.
> 
> The mechanism can always be sabotaged by memory-leak bugs on the part
> of the user of the kmem_cache structure in play, right?
> 
> OK, but I see your point.  I added this to the existing
> "kmem_cache_destroy() Lingers for kfree_rcu()" section:
> 
> 	One way of preserving this debugging information is to splat if
> 	all of the slab’s memory has not been freed within a reasonable
> 	timeframe, perhaps the same 21 seconds that causes an RCU CPU
> 	stall warning.
> 
> Does that capture it?

Not quite what I was thinking. Your 21 seconds as a time-based thing I
guess could be fine. But I was mostly thinking:

1) kmem_cache_destroy() is called, but there are outstanding objects, so
   it defers.

2) Sometime later, a kfree_rcu_work batch freeing operation runs.

3) At the end of this batch freeing, the kernel notices that the
   kmem_cache whose destruction was previously deferred still has
   outstanding objects and has not been destroyed. It can conclude that
   there's thus been a memory leak.

In other words, instead of having to do this based on timers, you can
just have the batch freeing code ask, "did those pending kmem_cache
destructions get completed as a result of this last operation?"

  reply	other threads:[~2024-06-13 14:12 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-06-09  8:27 Julia Lawall
2024-06-09  8:27 ` [PATCH 01/14] wireguard: allowedips: " Julia Lawall
2024-06-09 14:32   ` Jason A. Donenfeld
2024-06-09 14:36     ` Julia Lawall
2024-06-10 20:38     ` Vlastimil Babka
2024-06-10 20:59       ` Jason A. Donenfeld
2024-06-12 21:33 ` [PATCH 00/14] " Jakub Kicinski
2024-06-12 22:37   ` Paul E. McKenney
2024-06-12 22:46     ` Jakub Kicinski
2024-06-12 22:52     ` Jens Axboe
2024-06-12 23:04       ` Paul E. McKenney
2024-06-12 23:31     ` Jason A. Donenfeld
2024-06-13  0:31       ` Jason A. Donenfeld
2024-06-13  3:38         ` Paul E. McKenney
2024-06-13 12:22           ` Jason A. Donenfeld
2024-06-13 12:46             ` Paul E. McKenney
2024-06-13 14:11               ` Jason A. Donenfeld [this message]
2024-06-13 15:12                 ` Paul E. McKenney
2024-06-17 15:10             ` Vlastimil Babka
2024-06-17 16:12               ` Paul E. McKenney
2024-06-17 17:23                 ` Vlastimil Babka
2024-06-17 18:42                   ` Uladzislau Rezki
2024-06-17 21:08                     ` Vlastimil Babka
2024-06-18  9:31                       ` Uladzislau Rezki
2024-06-18 16:48                         ` Paul E. McKenney
2024-06-18 17:21                           ` Vlastimil Babka
2024-06-18 17:53                             ` Paul E. McKenney
2024-06-19  9:28                               ` Vlastimil Babka
2024-06-19 16:46                                 ` Paul E. McKenney
2024-06-21  9:32                                 ` Uladzislau Rezki
2024-07-15 20:39                                   ` Vlastimil Babka
2024-07-24 13:53                                     ` Paul E. McKenney
2024-07-24 14:40                                       ` Vlastimil Babka
2024-10-08 16:41                                       ` Vlastimil Babka
2024-10-08 20:02                                         ` Paul E. McKenney
2024-10-09 17:08                                           ` Julia Lawall
2024-10-09 21:02                                             ` Paul E. McKenney
2024-06-19  9:51                           ` Uladzislau Rezki
2024-06-19  9:56                             ` Vlastimil Babka
2024-06-19 11:22                               ` Uladzislau Rezki
2024-06-17 18:54                   ` Paul E. McKenney
2024-06-17 21:34                     ` Vlastimil Babka
2024-06-13 14:17           ` Jakub Kicinski
2024-06-13 14:53             ` Paul E. McKenney
2024-06-13 11:58     ` Jason A. Donenfeld
2024-06-13 12:47       ` Paul E. McKenney
2024-06-13 13:06         ` Uladzislau Rezki
2024-06-13 15:06           ` Paul E. McKenney
2024-06-13 17:38             ` Uladzislau Rezki
2024-06-13 17:45               ` Paul E. McKenney
2024-06-13 17:58                 ` Uladzislau Rezki
2024-06-13 18:13                   ` Paul E. McKenney
2024-06-14 12:35                     ` Uladzislau Rezki
2024-06-14 14:17                       ` Paul E. McKenney
2024-06-14 14:50                         ` Uladzislau Rezki
2024-06-14 19:33                       ` Jason A. Donenfeld
2024-06-17 13:50                         ` Uladzislau Rezki
2024-06-17 14:56                           ` Jason A. Donenfeld
2024-06-17 16:30                             ` Uladzislau Rezki
2024-06-17 16:33                               ` Jason A. Donenfeld
2024-06-17 16:38                                 ` Vlastimil Babka
2024-06-17 17:04                                   ` Jason A. Donenfeld
2024-06-17 21:19                                     ` Vlastimil Babka
2024-06-17 16:42                                 ` Uladzislau Rezki
2024-06-17 16:57                                   ` Jason A. Donenfeld
2024-06-17 17:19                                     ` Uladzislau Rezki
2024-06-17 14:37                         ` Vlastimil Babka
2024-10-08 16:36 ` Vlastimil Babka

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