From: "Luis R. Rodriguez" <mcgrof@kernel.org>
To: shuah@kernel.org, jeyu@redhat.com, rusty@rustcorp.com.au,
ebiederm@xmission.com, dmitry.torokhov@gmail.com,
acme@redhat.com, corbet@lwn.net
Cc: 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,
"Luis R. Rodriguez" <mcgrof@kernel.org>
Subject: [PATCH 5/6] kmod: preempt on kmod_umh_threads_get()
Date: Thu, 18 May 2017 20:24:43 -0700 [thread overview]
Message-ID: <20170519032444.18416-6-mcgrof@kernel.org> (raw)
In-Reply-To: <20170519032444.18416-1-mcgrof@kernel.org>
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)
- return 0;
+ goto out;
+
atomic_dec(&kmod_concurrent);
- return -EBUSY;
+ ret = -EBUSY;
+out:
+ preempt_enable();
+ return ret;
}
static void kmod_umh_threads_put(void)
{
+ /*
+ * Preemption is not needed given once work is done we can
+ * pace ourselves on our way out.
+ */
atomic_dec(&kmod_concurrent);
}
--
2.11.0
next prev parent reply other threads:[~2017-05-19 3:25 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 ` Luis R. Rodriguez [this message]
2017-05-19 22:27 ` [PATCH 5/6] kmod: preempt on kmod_umh_threads_get() Dmitry Torokhov
2017-05-25 0:14 ` Luis R. Rodriguez
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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