From: "Luis R. Rodriguez" <mcgrof@kernel.org>
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>,
shuah@kernel.org, jeyu@redhat.com, rusty@rustcorp.com.au,
ebiederm@xmission.com, acme@redhat.com, corbet@lwn.net,
martin.wilck@suse.com, mmarek@suse.com, pmladek@suse.com,
hare@suse.com, rwright@hpe.com, jeffm@suse.com, DSterba@suse.com,
fdmanana@suse.com, neilb@suse.com, linux@roeck-us.net,
rgoldwyn@suse.com, subashab@codeaurora.org, xypron.glpk@gmx.de,
keescook@chromium.org, atomlin@redhat.com, mbenes@suse.cz,
paulmck@linux.vnet.ibm.com, dan.j.williams@intel.com,
jpoimboe@redhat.com, davem@davemloft.net, mingo@redhat.com,
akpm@linux-foundation.org, torvalds@linux-foundation.org,
gregkh@linuxfoundation.org, linux-kselftest@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 5/6] kmod: preempt on kmod_umh_threads_get()
Date: Thu, 25 May 2017 02:14:52 +0200 [thread overview]
Message-ID: <20170525001452.GS8951@wotan.suse.de> (raw)
In-Reply-To: <20170519222712.GI19281@dtor-ws>
On Fri, May 19, 2017 at 03:27:12PM -0700, Dmitry Torokhov wrote:
> On Thu, May 18, 2017 at 08:24:43PM -0700, Luis R. Rodriguez wrote:
> > In theory it is possible multiple concurrent threads will try to
> > kmod_umh_threads_get() and as such atomic_inc(&kmod_concurrent) at
> > the same time, therefore enabling a small time during which we've
> > bumped kmod_concurrent but have not really enabled work. By using
> > preemption we mitigate this a bit.
> >
> > Preemption is not needed when we kmod_umh_threads_put().
> >
> > Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
> > ---
> > kernel/kmod.c | 24 ++++++++++++++++++++++--
> > 1 file changed, 22 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/kmod.c b/kernel/kmod.c
> > index 563600fc9bb1..7ea11dbc7564 100644
> > --- a/kernel/kmod.c
> > +++ b/kernel/kmod.c
> > @@ -113,15 +113,35 @@ static int call_modprobe(char *module_name, int wait)
> >
> > static int kmod_umh_threads_get(void)
> > {
> > + int ret = 0;
> > +
> > + /*
> > + * Disabling preemption makes sure that we are not rescheduled here
> > + *
> > + * Also preemption helps kmod_concurrent is not increased by mistake
> > + * for too long given in theory two concurrent threads could race on
> > + * atomic_inc() before we atomic_read() -- we know that's possible
> > + * and but we don't care, this is not used for object accounting and
> > + * is just a subjective threshold. The alternative is a lock.
> > + */
> > + preempt_disable();
> > atomic_inc(&kmod_concurrent);
> > if (atomic_read(&kmod_concurrent) <= max_modprobes)
>
> That is very "fancy" way to basically say:
>
> if (atomic_inc_return(&kmod_concurrent) <= max_modprobes)
Do you mean to combine the atomic_inc() and atomic_read() in one as you noted
(as that is not a change in this patch), *or* that using a memory barrier here
with atomic_inc_return() should suffice to address the same and avoid an
explicit preemption enable / disable ?
Luis
next prev parent reply other threads:[~2017-05-25 0:15 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-19 3:24 [PATCH 0/6] kmod: few simple enhancements Luis R. Rodriguez
2017-05-19 3:24 ` [PATCH 1/6] kmod: add dynamic max concurrent thread count Luis R. Rodriguez
2017-05-19 20:44 ` Dmitry Torokhov
[not found] ` <CAB=NE6XGL24O+JfTNUG0HO4obhDc-v+HyL0SCrQELiZrj2-qNw@mail.gmail.com>
[not found] ` <CAB=NE6Wa4Nemh80yaCCwbjrNRLPD+GJMncg12APg9Vq63AWVng@mail.gmail.com>
[not found] ` <CAB=NE6Vc6RDAytn2Pkv2V58HFo8ncR0eOHZ3===kbZ2NF78ubg@mail.gmail.com>
[not found] ` <CAB=NE6Vqmx=y6muenpuQKynTP=pGWMF8tzoCA0BXD6d63q9wPg@mail.gmail.com>
2017-05-19 21:58 ` Dmitry Torokhov
2017-05-25 16:22 ` Luis R. Rodriguez
2017-05-25 16:38 ` Dmitry Torokhov
2017-05-25 16:50 ` Luis R. Rodriguez
2017-05-25 17:30 ` Dmitry Torokhov
2017-05-25 17:38 ` Luis R. Rodriguez
2017-05-25 18:06 ` Luis R. Rodriguez
2017-05-25 18:26 ` Dmitry Torokhov
2017-05-25 19:01 ` Luis R. Rodriguez
2017-05-25 21:38 ` Luis R. Rodriguez
2017-05-19 3:24 ` [PATCH 2/6] module: use list_for_each_entry_rcu() on find_module_all() Luis R. Rodriguez
2017-05-23 14:46 ` Miroslav Benes
2017-05-19 3:24 ` [PATCH 3/6] kmod: provide wrappers for kmod_concurrent inc/dec Luis R. Rodriguez
2017-05-19 3:24 ` [PATCH 4/6] kmod: return -EBUSY if modprobe limit is reached Luis R. Rodriguez
2017-05-19 3:24 ` [PATCH 5/6] kmod: preempt on kmod_umh_threads_get() Luis R. Rodriguez
2017-05-19 22:27 ` Dmitry Torokhov
2017-05-25 0:14 ` Luis R. Rodriguez [this message]
2017-05-25 0:45 ` Dmitry Torokhov
2017-05-25 1:00 ` Luis R. Rodriguez
2017-05-25 2:27 ` Dmitry Torokhov
2017-05-25 11:19 ` Petr Mladek
2017-05-25 15:38 ` Luis R. Rodriguez
2017-05-25 16:42 ` Dmitry Torokhov
2017-05-25 15:18 ` Jessica Yu
2017-05-19 3:24 ` [PATCH 6/6] kmod: use simplified rate limit printk Luis R. Rodriguez
2017-05-19 22:23 ` Dmitry Torokhov
2017-05-23 9:00 ` Petr Mladek
2017-05-26 0:16 ` [PATCH v2 0/5] kmod: help make deterministic Luis R. Rodriguez
2017-05-26 0:16 ` [PATCH v2 1/5] module: use list_for_each_entry_rcu() on find_module_all() Luis R. Rodriguez
2017-05-26 0:16 ` [PATCH v2 2/5] kmod: reduce atomic operations on kmod_concurrent Luis R. Rodriguez
2017-05-26 1:11 ` Dmitry Torokhov
2017-05-26 20:03 ` Luis R. Rodriguez
2017-05-26 0:16 ` [PATCH v2 3/5] kmod: add test driver to stress test the module loader Luis R. Rodriguez
2017-05-26 0:16 ` [PATCH v2 4/5] kmod: add helpers for getting kmod limit Luis R. Rodriguez
2017-05-26 0:56 ` Dmitry Torokhov
2017-05-26 20:27 ` Luis R. Rodriguez
2017-05-26 0:16 ` [PATCH v2 5/5] kmod: throttle kmod thread limit Luis R. Rodriguez
2017-05-26 21:12 ` [PATCH v3 0/4] kmod: help make deterministic Luis R. Rodriguez
2017-05-26 21:12 ` [PATCH v3 1/4] module: use list_for_each_entry_rcu() on find_module_all() Luis R. Rodriguez
2017-05-26 21:12 ` [PATCH v3 2/4] kmod: reduce atomic operations on kmod_concurrent and simplify Luis R. Rodriguez
2017-06-23 19:19 ` [PATCH v4 " Luis R. Rodriguez
2017-06-26 11:36 ` [PATCH v3 " Petr Mladek
2017-05-26 21:12 ` [PATCH v3 3/4] kmod: add test driver to stress test the module loader Luis R. Rodriguez
2017-05-26 21:12 ` [PATCH v3 4/4] kmod: throttle kmod thread limit Luis R. Rodriguez
2017-06-22 15:19 ` Petr Mladek
2017-06-23 16:16 ` Luis R. Rodriguez
2017-06-23 17:56 ` Luis R. Rodriguez
2017-06-23 19:16 ` Luis R. Rodriguez
2017-06-26 10:03 ` Petr Mladek
2017-06-26 9:55 ` Petr Mladek
2017-06-23 19:20 ` [PATCH v4 " Luis R. Rodriguez
2017-06-26 11:38 ` Petr Mladek
2017-06-28 22:11 ` Luis R. Rodriguez
2017-06-20 20:56 ` [PATCH v3 0/4] kmod: help make deterministic Luis R. Rodriguez
2017-06-21 0:23 ` Kees Cook
2017-06-26 21:37 ` Jessica Yu
2017-06-26 22:44 ` Luis R. Rodriguez
2017-06-27 0:27 ` Luis R. Rodriguez
2017-06-27 8:13 ` Petr Mladek
2017-06-27 10:04 ` Jessica Yu
2017-06-27 15:26 ` Jessica Yu
2017-06-28 0:49 ` Luis R. Rodriguez
2017-06-28 22:31 ` [PATCH v4 0/3] " Luis R. Rodriguez
2017-06-28 22:31 ` [PATCH v4 1/3] MAINTAINERS: give kmod some maintainer love Luis R. Rodriguez
2017-06-28 22:31 ` [PATCH v4 2/3] kmod: add test driver to stress test the module loader Luis R. Rodriguez
2017-06-28 22:31 ` [PATCH v4 3/3] kmod: throttle kmod thread limit Luis R. Rodriguez
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