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

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Message-ID: <20200520164556.GC11084@rowland.harvard.edu>
Date:   Wed, 20 May 2020 12:45:56 -0400
From:   "stern@...land.harvard.edu" <stern@...land.harvard.edu>
To:     "Sverdlin, Alexander \(Nokia - DE/Ulm\)" 
        <alexander.sverdlin@...ia.com>
Cc:     "dinghao.liu@....edu.cn" <dinghao.liu@....edu.cn>,
        "kjlu@....edu" <kjlu@....edu>, "mpm@...enic.com" <mpm@...enic.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
        "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>
Subject: Re: [PATCH] hwrng: ks-sa - fix runtime pm imbalance on error

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.

You really shouldn't make generalizations such as "no other driver does 
..." unless you have read the code for every driver in the kernel.

Alan Stern