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Date:   Thu, 28 May 2020 11:39:14 -0400
From:   "stern@rowland.harvard.edu" <stern@rowland.harvard.edu>
To:     Herbert Xu <herbert@gondor.apana.org.au>
Cc:     "Sverdlin, Alexander \(Nokia - DE/Ulm\)" 
        <alexander.sverdlin@nokia.com>,
        "dinghao.liu@zju.edu.cn" <dinghao.liu@zju.edu.cn>,
        "kjlu@umn.edu" <kjlu@umn.edu>, "mpm@selenic.com" <mpm@selenic.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "ben.dooks@codethink.co.uk" <ben.dooks@codethink.co.uk>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "arnd@arndb.de" <arnd@arndb.de>,
        "allison@lohutok.net" <allison@lohutok.net>,
        "yuehaibing@huawei.com" <yuehaibing@huawei.com>,
        "rfontana@redhat.com" <rfontana@redhat.com>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Subject: Re: [PATCH] hwrng: ks-sa - fix runtime pm imbalance on error
Message-ID: <20200528153914.GA11831@rowland.harvard.edu>
References: <20200520132957.18776-1-dinghao.liu@zju.edu.cn>
 <ab400cba7523e69b15360b0928cb8fa8b9432d86.camel@nokia.com>
 <20200520164556.GC11084@rowland.harvard.edu>
 <20200528065519.GA26960@gondor.apana.org.au>
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On Thu, May 28, 2020 at 04:55:19PM +1000, Herbert Xu wrote:
> On Wed, May 20, 2020 at 12:45:56PM -0400, stern@rowland.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