linux-kernel - RE: [PATCH] mtd: use refcount to prevent corruption

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Date:   Wed, 27 Jan 2021 20:55:46 +0000
From:   "Winkler, Tomas" <tomas.winkler@...el.com>
To:     Richard Weinberger <richard@....at>
CC:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] mtd: use refcount to prevent corruption


> Subject: Re: [PATCH] mtd: use refcount to prevent corruption
> 
> Tomas,
> 
> ----- Ursprüngliche Mail -----
> > Von: "Tomas Winkler" <tomas.winkler@...el.com>
> > An: "Miquel Raynal" <miquel.raynal@...tlin.com>, "richard"
> > <richard@....at>, "Vignesh Raghavendra" <vigneshr@...com>, "linux-mtd"
> > <linux-mtd@...ts.infradead.org>, "linux-kernel"
> > <linux-kernel@...r.kernel.org>
> > CC: "Tomas Winkler" <tomas.winkler@...el.com>
> > Gesendet: Mittwoch, 27. Januar 2021 21:03:19
> > Betreff: [PATCH] mtd: use refcount to prevent corruption
> 
> > When underlying device is removed mtd core will crash in case user
> > space is still holding an open handle to a mtd device node.
> > A proper refcounting is needed so device is release only when a
> > partition has no active users. The current simple counter is not
> > sufficient.
> 
> Can you please explain a little more what devices are involved?
> Does it implement _get_device() and _put_device()?
No this is not connected to those handlers of the underlying device and those won't help. 
I have a spi device provided by MFD framework so it can go away anytime. 
My solution tries to  replace the current simple partition reference counting.  In previous solution it will return -EBUSY on partition that is held but will remove the actual parent device, leading to crash.
Also w/o reference counting there is no process to actually remove the partition that was previously busy.

Thanks
Tomas



> 
> Thanks,
> //richard