From: Uladzislau Rezki <urezki@gmail.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Uladzislau Rezki <urezki@gmail.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
"Jason A. Donenfeld" <Jason@zx2c4.com>,
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,
kasan-dev <kasan-dev@googlegroups.com>
Subject: Re: [PATCH 00/14] replace call_rcu by kfree_rcu for simple kmem_cache_free callback
Date: Wed, 19 Jun 2024 13:22:12 +0200 [thread overview]
Message-ID: <ZnK_ZLlFM6MrdEah@pc636> (raw)
In-Reply-To: <c208e95d-9aa9-476f-9dee-0242a2d6a24f@suse.cz>
On Wed, Jun 19, 2024 at 11:56:44AM +0200, Vlastimil Babka wrote:
> On 6/19/24 11:51 AM, Uladzislau Rezki wrote:
> > On Tue, Jun 18, 2024 at 09:48:49AM -0700, Paul E. McKenney wrote:
> >> On Tue, Jun 18, 2024 at 11:31:00AM +0200, Uladzislau Rezki wrote:
> >> > > On 6/17/24 8:42 PM, Uladzislau Rezki wrote:
> >> > > >> +
> >> > > >> + s = container_of(work, struct kmem_cache, async_destroy_work);
> >> > > >> +
> >> > > >> + // XXX use the real kmem_cache_free_barrier() or similar thing here
> >> > > > It implies that we need to introduce kfree_rcu_barrier(), a new API, which i
> >> > > > wanted to avoid initially.
> >> > >
> >> > > I wanted to avoid new API or flags for kfree_rcu() users and this would
> >> > > be achieved. The barrier is used internally so I don't consider that an
> >> > > API to avoid. How difficult is the implementation is another question,
> >> > > depending on how the current batching works. Once (if) we have sheaves
> >> > > proven to work and move kfree_rcu() fully into SLUB, the barrier might
> >> > > also look different and hopefully easier. So maybe it's not worth to
> >> > > invest too much into that barrier and just go for the potentially
> >> > > longer, but easier to implement?
> >> > >
> >> > Right. I agree here. If the cache is not empty, OK, we just defer the
> >> > work, even we can use a big 21 seconds delay, after that we just "warn"
> >> > if it is still not empty and leave it as it is, i.e. emit a warning and
> >> > we are done.
> >> >
> >> > Destroying the cache is not something that must happen right away.
> >>
> >> OK, I have to ask...
> >>
> >> Suppose that the cache is created and destroyed by a module and
> >> init/cleanup time, respectively. Suppose that this module is rmmod'ed
> >> then very quickly insmod'ed.
> >>
> >> Do we need to fail the insmod if the kmem_cache has not yet been fully
> >> cleaned up? If not, do we have two versions of the same kmem_cache in
> >> /proc during the overlap time?
> >>
> > No fail :) If same cache is created several times, its s->refcount gets
> > increased, so, it does not create two entries in the "slabinfo". But i
> > agree that your point is good! We need to be carefully with removing and
> > simultaneous creating.
>
> Note that this merging may be disabled or not happen due to various flags on
> the cache being incompatible with it. And I want to actually make sure it
> never happens for caches being already destroyed as that would lead to
> use-after-free (the workfn doesn't recheck the refcount in case a merge
> would happen during the grace period)
>
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -150,9 +150,10 @@ int slab_unmergeable(struct kmem_cache *s)
> #endif
>
> /*
> - * We may have set a slab to be unmergeable during bootstrap.
> + * We may have set a cache to be unmergeable during bootstrap.
> + * 0 is for cache being destroyed asynchronously
> */
> - if (s->refcount < 0)
> + if (s->refcount <= 0)
> return 1;
>
> return 0;
>
OK, i see such flags, SLAB_NO_MERGE. Then i was wrong, it can create two
different slabs.
Thanks!
--
Uladzislau Rezki
next prev parent reply other threads:[~2024-06-19 11:25 UTC|newest]
Thread overview: 59+ 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
[not found] ` <7e58e73d-4173-49fe-8f05-38a3699bc2c1@kernel.dk>
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
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
2024-06-19 9:51 ` Uladzislau Rezki
2024-06-19 9:56 ` Vlastimil Babka
2024-06-19 11:22 ` Uladzislau Rezki [this message]
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
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