From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jessica Yu <jeyu@kernel.org>,
linux-kernel@vger.kernel.org, jikos@kernel.org, mbenes@suse.cz,
pmladek@suse.com, ast@kernel.org, daniel@iogearbox.net,
akpm@linux-foundation.org,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Pavel Machek <pavel@ucw.cz>, Len Brown <len.brown@intel.com>,
Sam Protsenko <semen.protsenko@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Alexios Zavras <alexios.zavras@intel.com>,
Allison Randal <allison@lohutok.net>,
Vasily Averin <vvs@virtuozzo.com>,
Todd Brandt <todd.e.brandt@linux.intel.com>,
linux-pm@vger.kernel.org
Subject: Re: [PATCH 1/3] notifier: Fix broken error handling pattern
Date: Tue, 25 Jun 2019 09:38:21 +0200 [thread overview]
Message-ID: <20190625073821.GQ3436@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190624222107.wrmtww6b2be26wwl@treble>
On Mon, Jun 24, 2019 at 05:21:07PM -0500, Josh Poimboeuf wrote:
> On Mon, Jun 24, 2019 at 11:18:44AM +0200, Peter Zijlstra wrote:
> > The current notifiers have the following error handling pattern all
> > over the place:
> >
> > int nr;
> >
> > ret = __foo_notifier_call_chain(&chain, val_up, v, -1, &nr);
> > if (err & NOTIFIER_STOP_MASK)
>
> s/err/ret/
-ETOOWARM :-)
> > __foo_notifier_call_chain(&chain, val_down, v, nr-1, NULL)
> >
> > And aside from the endless repetition thereof, it is broken. Consider
> > blocking notifiers; both calls take and drop the rwsem, this means
> > that the notifier list can change in between the two calls, making @nr
> > meaningless.
> >
> > Fix this by replacing all the __foo_notifier_call_chain() functions
> > with foo_notifier_call_chain_error() that embeds the above patter, but
> > ensures it is inside a single lock region.
>
> The name "notifier_call_chain_error()" seems confusing, it almost sounds
> like it's notifying an error code. Then again, I can't really think of
> a more reasonably succinct name.
I;m not attached to the name; I very much ran out of ideas and just
typed something.
> > @@ -25,8 +25,23 @@ static int cpu_pm_notify(enum cpu_pm_eve
> > * RCU know this.
> > */
> > rcu_irq_enter_irqson();
> > - ret = __atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL,
> > - nr_to_call, nr_calls);
> > + ret = atomic_notifier_call_chain(&cpu_pm_notifier_chain, event, NULL);
> > + rcu_irq_exit_irqson();
> > +
> > + return notifier_to_errno(ret);
> > +}
> > +
> > +static int cpu_pm_notify_error(enum cpu_pm_event event_up, enum cpu_pm_event event_down)
> > +{
> > + int ret;
> > +
> > + /*
> > + * __atomic_notifier_call_chain has a RCU read critical section, which
>
> __atomic_notifier_call_chain() no longer exists.
>
> > + * could be disfunctional in cpu idle. Copy RCU_NONIDLE code to let
>
> "dysfunctional"
That's copy paste, I don't think I've read the comment, my bad.
> > @@ -156,43 +169,30 @@ int atomic_notifier_chain_unregister(str
> > }
> > EXPORT_SYMBOL_GPL(atomic_notifier_chain_unregister);
> >
> > -/**
> > - * __atomic_notifier_call_chain - Call functions in an atomic notifier chain
> > - * @nh: Pointer to head of the atomic notifier chain
> > - * @val: Value passed unmodified to notifier function
> > - * @v: Pointer passed unmodified to notifier function
> > - * @nr_to_call: See the comment for notifier_call_chain.
> > - * @nr_calls: See the comment for notifier_call_chain.
> > - *
> > - * Calls each function in a notifier chain in turn. The functions
> > - * run in an atomic context, so they must not block.
> > - * This routine uses RCU to synchronize with changes to the chain.
> > - *
> > - * If the return value of the notifier can be and'ed
> > - * with %NOTIFY_STOP_MASK then atomic_notifier_call_chain()
> > - * will return immediately, with the return value of
> > - * the notifier function which halted execution.
> > - * Otherwise the return value is the return value
> > - * of the last notifier function called.
> > - */
>
> Why remove the useful comment?
Because I delete the whole function ?
next prev parent reply other threads:[~2019-06-25 7:39 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190624091843.859714294@infradead.org>
2019-06-24 9:18 ` [PATCH 1/3] notifier: Fix broken error handling pattern Peter Zijlstra
2019-06-24 22:21 ` Josh Poimboeuf
2019-06-25 7:38 ` Peter Zijlstra [this message]
2019-06-25 12:13 ` Josh Poimboeuf
2019-06-25 13:22 ` Peter Zijlstra
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=20190625073821.GQ3436@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=akpm@linux-foundation.org \
--cc=alexios.zavras@intel.com \
--cc=allison@lohutok.net \
--cc=ast@kernel.org \
--cc=daniel@iogearbox.net \
--cc=gregkh@linuxfoundation.org \
--cc=jeyu@kernel.org \
--cc=jikos@kernel.org \
--cc=jpoimboe@redhat.com \
--cc=len.brown@intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pm@vger.kernel.org \
--cc=mbenes@suse.cz \
--cc=pavel@ucw.cz \
--cc=pmladek@suse.com \
--cc=rjw@rjwysocki.net \
--cc=semen.protsenko@linaro.org \
--cc=tglx@linutronix.de \
--cc=todd.e.brandt@linux.intel.com \
--cc=vvs@virtuozzo.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).