linux-kernel - Re: [PATCH] hwrng: ks-sa - fix runtime pm imbalance on error

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Message-ID: <20200528153914.GA11831@rowland.harvard.edu>
Date:   Thu, 28 May 2020 11:39:14 -0400
From:   "stern@...land.harvard.edu" <stern@...land.harvard.edu>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     "Sverdlin, Alexander \(Nokia - DE/Ulm\)" 
        <alexander.sverdlin@...ia.com>,
        "dinghao.liu@....edu.cn" <dinghao.liu@....edu.cn>,
        "kjlu@....edu" <kjlu@....edu>, "mpm@...enic.com" <mpm@...enic.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "ben.dooks@...ethink.co.uk" <ben.dooks@...ethink.co.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "allison@...utok.net" <allison@...utok.net>,
        "yuehaibing@...wei.com" <yuehaibing@...wei.com>,
        "rfontana@...hat.com" <rfontana@...hat.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] hwrng: ks-sa - fix runtime pm imbalance on error

On Thu, May 28, 2020 at 04:55:19PM +1000, Herbert Xu wrote:
> On Wed, May 20, 2020 at 12:45:56PM -0400, stern@...land.harvard.edu wrote:
> > On Wed, May 20, 2020 at 03:42:17PM +0000, Sverdlin, Alexander (Nokia - DE/Ulm) wrote:
> > > Hello Dinghao,
> > > 
> > > On Wed, 2020-05-20 at 21:29 +0800, Dinghao Liu wrote:
> > > > pm_runtime_get_sync() increments the runtime PM usage counter even
> > > > the call returns an error code. Thus a pairing decrement is needed
> > > > on the error handling path to keep the counter balanced.
> > > 
> > > I believe, this is the wrong place for such kind of fix.
> > > pm_runtime_get_sync() has obviously a broken semantics with regards to
> > > your observation but no other driver does what you propose.
> > 
> > Look again.  For example, see what usb_autoresume_device() in 
> > drivers/usb/core/driver.c does.
> 
> However, there seems to be some disagreement as to what to do
> when pm_runtime_get_sync fails.  Your driver chooses to call
> put_sync while others prefer pm_runtime_put_noidle (e.g., see
> drivers/base/power/runtime.c).

It doesn't matter which function gets called; in these circumstances 
(device still suspended or in an error state because a resume attempt 
failed) they will do the same thing.

> This API does seem to be in a bit of a mess.

Suggestions and patches are welcome.

Alan Stern