linux-kernel - Re: [PATCH v2 2/2] arm: perf: Mark as non-removable

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Message-ID: <20170104114056.GO14217@n2100.armlinux.org.uk>
Date:   Wed, 4 Jan 2017 11:40:56 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Alexander Stein <alexander.stein@...tec-electronic.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/2] arm: perf: Mark as non-removable

On Wed, Jan 04, 2017 at 11:30:25AM +0000, Mark Rutland wrote:
> On Wed, Jan 04, 2017 at 10:19:46AM +0100, Alexander Stein wrote:
> > I'm not sure if the change above works with remove functions set in struct 
> > bus_type too.
> > But on the other hand this would hide errors in drivers which are actually 
> > removable but do not cleanup properly which DEBUG_TEST_DRIVER_REMOVE tries to 
> > detect.
> > By setting .suppress_bind_attrs = true explicitely you state "This 
> > driver cannot be removed!", so the remove callback is not missing by accident.
> 
> I'm not sure I follow. If the remove callback is accidentally missing,
> the driver is not "actually removable" today -- there's either no remove
> code, or it's not been wired up (the latter of which will likely result
> in a compiler warning about an unused function).
> 
> Aborting the remove early in those cases is much safer than forcefully
> removing a driver without a remove callback.

Drivers without a remove function may be removable - there's more layers
than just the driver - there's the bus layer as well, which may or may
not direct to a private-bus pointer.

There's no real way for the core driver model code to know whether the
lack of the ->remove in the struct device_driver is something that
prevents a driver being removed, or whether it's handled via some other
method.  Eg, platform drivers.

-- 
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