LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Petr Mladek <pmladek@suse.com>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: akpm@linux-foundation.org, jeyu@redhat.com, shuah@kernel.org,
	rusty@rustcorp.com.au, ebiederm@xmission.com,
	dmitry.torokhov@gmail.com, acme@redhat.com, corbet@lwn.net,
	josh@joshtriplett.org, martin.wilck@suse.com, mmarek@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,
	alan@linux.intel.com, tytso@mit.edu, gregkh@linuxfoundation.org,
	torvalds@linux-foundation.org, linux-kselftest@vger.kernel.org,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 4/4] kmod: throttle kmod thread limit
Date: Mon, 26 Jun 2017 11:55:26 +0200
Message-ID: <20170626095526.GG1538@pathway.suse.cz> (raw)
In-Reply-To: <20170623161619.GL21846@wotan.suse.de>

On Fri 2017-06-23 18:16:19, Luis R. Rodriguez wrote:
> On Thu, Jun 22, 2017 at 05:19:36PM +0200, Petr Mladek wrote:
> > On Fri 2017-05-26 14:12:28, Luis R. Rodriguez wrote:
> > > --- a/kernel/kmod.c
> > > +++ b/kernel/kmod.c
> > > @@ -163,14 +163,11 @@ int __request_module(bool wait, const char *fmt, ...)
> > >  		return ret;
> > >  
> > >  	if (atomic_dec_if_positive(&kmod_concurrent_max) < 0) {
> > > -		/* We may be blaming an innocent here, but unlikely */
> > > -		if (kmod_loop_msg < 5) {
> > > -			printk(KERN_ERR
> > > -			       "request_module: runaway loop modprobe %s\n",
> > > -			       module_name);
> > > -			kmod_loop_msg++;
> > > -		}
> > > -		return -ENOMEM;
> > > +		pr_warn_ratelimited("request_module: kmod_concurrent_max (%u) close to 0 (max_modprobes: %u), for module %s\n, throttling...",
> > > +				    atomic_read(&kmod_concurrent_max),
> > > +				    50, module_name);
> > 
> > It is weird to pass the constant '50' via %s.
> 
> The 50 was passed with %u, so I take it you meant it is odd to use a parameter
> for it.

Yeah, I meant %u and not %s.

> > Also a #define should be
> > used to keep it in sync with the kmod_concurrent_max initialization.
> 
> OK.
> 
> > > +		wait_event_interruptible(kmod_wq,
> > > +					 atomic_dec_if_positive(&kmod_concurrent_max) >= 0);
> > >  	}
> > >  
> > >  	trace_module_request(module_name, wait, _RET_IP_);
> > > @@ -178,6 +175,7 @@ int __request_module(bool wait, const char *fmt, ...)
> > >  	ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
> > >  
> > >  	atomic_inc(&kmod_concurrent_max);
> > > +	wake_up_all(&kmod_wq);
> > 
> > Does it make sense to wake up all waiters when we released the resource
> > only for one? IMHO, a simple wake_up() should be here.
> 
> Then we should wake_up() also on failure, otherwise we have the potential
> to not wake some in a proper time.

I think that we must wake_up() always when we increment
kmod_concurrent_max. If the value was negative, the increment will
allow exactly one process to pass that
atomic_dec_if_positive(&kmod_concurrent_max) >= 0). It the value
is positive, there must have been other wake_up() calls or there
is no waiter.

IMHO, this works because kmod_concurrent_max handling is atomic
and race-less now. Also (s)wait_event_interruptible() is safe
and does not allow to get into sleep when the resource is available.

Anyway, it is great that you have double checked this.

Best Regards,
Petr

  parent reply index

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
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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20170626095526.GG1538@pathway.suse.cz \
    --to=pmladek@suse.com \
    --cc=DSterba@suse.com \
    --cc=acme@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=alan@linux.intel.com \
    --cc=atomlin@redhat.com \
    --cc=corbet@lwn.net \
    --cc=dan.j.williams@intel.com \
    --cc=davem@davemloft.net \
    --cc=dmitry.torokhov@gmail.com \
    --cc=ebiederm@xmission.com \
    --cc=fdmanana@suse.com \
    --cc=gregkh@linuxfoundation.org \
    --cc=hare@suse.com \
    --cc=jeffm@suse.com \
    --cc=jeyu@redhat.com \
    --cc=josh@joshtriplett.org \
    --cc=jpoimboe@redhat.com \
    --cc=keescook@chromium.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=linux@roeck-us.net \
    --cc=martin.wilck@suse.com \
    --cc=mbenes@suse.cz \
    --cc=mcgrof@kernel.org \
    --cc=mingo@redhat.com \
    --cc=mmarek@suse.com \
    --cc=neilb@suse.com \
    --cc=paulmck@linux.vnet.ibm.com \
    --cc=rgoldwyn@suse.com \
    --cc=rusty@rustcorp.com.au \
    --cc=rwright@hpe.com \
    --cc=shuah@kernel.org \
    --cc=subashab@codeaurora.org \
    --cc=torvalds@linux-foundation.org \
    --cc=tytso@mit.edu \
    --cc=xypron.glpk@gmx.de \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git