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From: "Winkler, Tomas" <tomas.winkler@intel.com>
To: Richard Weinberger <richard@nod.at>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
	linux-mtd <linux-mtd@lists.infradead.org>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Miquel Raynal <miquel.raynal@bootlin.com>
Subject: RE: [PATCH] mtd: use refcount to prevent corruption
Date: Thu, 28 Jan 2021 08:53:43 +0000	[thread overview]
Message-ID: <f91d7eff1d764ba7b47f023bc0fafacb@intel.com> (raw)
In-Reply-To: <1665542284.336646.1611820031174.JavaMail.zimbra@nod.at>



> Tomas,
> 
> ----- Ursprüngliche Mail -----
> >> >> 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.
> >>
> >> Can it go away physically or just in software?
> > Software, but since this is mfd it's basically hotplug. The kernel is
> > crashing when I simulate hardware failure.
> >>
> >> Usually the pattern is that you make sure in the device driver that
> >> nobody can orphan the MTD while it is in use.
> >> e.g. drivers/mtd/ubi/gluebi.c does so. In _get_device() it grabs a
> >> reference on the underlying UBI volume to make sure it cannot go away
> >> while the MTD (on top of UBI) is in use.
> >
> > I can try that if it helps, because we are simulating possible lower
> > level crash.
> > In an case I believe that the proper refcouting is much more robust
> > solution, than the current one.
> > I'd appreciate if someone can review the actual implementation.
> 
> This happens right now, I try to understand why exactly the current way is not
> good in enough. :-)
> 
> Your approach makes sure that the MTD itself does not go away while it has
> users but how does this help in the case where the underlying MFD just
> vanishes?
> The MTD can be in use and the MFD can go away while e.g. mtd_read() or such
> takes place.

Read will fail, but kernel won't crash on access to memory that was freed.

Thanks
Tomas


______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/

WARNING: multiple messages have this Message-ID (diff)
From: "Winkler, Tomas" <tomas.winkler@intel.com>
To: Richard Weinberger <richard@nod.at>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	linux-mtd <linux-mtd@lists.infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] mtd: use refcount to prevent corruption
Date: Thu, 28 Jan 2021 08:53:43 +0000	[thread overview]
Message-ID: <f91d7eff1d764ba7b47f023bc0fafacb@intel.com> (raw)
In-Reply-To: <1665542284.336646.1611820031174.JavaMail.zimbra@nod.at>



> Tomas,
> 
> ----- Ursprüngliche Mail -----
> >> >> 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.
> >>
> >> Can it go away physically or just in software?
> > Software, but since this is mfd it's basically hotplug. The kernel is
> > crashing when I simulate hardware failure.
> >>
> >> Usually the pattern is that you make sure in the device driver that
> >> nobody can orphan the MTD while it is in use.
> >> e.g. drivers/mtd/ubi/gluebi.c does so. In _get_device() it grabs a
> >> reference on the underlying UBI volume to make sure it cannot go away
> >> while the MTD (on top of UBI) is in use.
> >
> > I can try that if it helps, because we are simulating possible lower
> > level crash.
> > In an case I believe that the proper refcouting is much more robust
> > solution, than the current one.
> > I'd appreciate if someone can review the actual implementation.
> 
> This happens right now, I try to understand why exactly the current way is not
> good in enough. :-)
> 
> Your approach makes sure that the MTD itself does not go away while it has
> users but how does this help in the case where the underlying MFD just
> vanishes?
> The MTD can be in use and the MFD can go away while e.g. mtd_read() or such
> takes place.

Read will fail, but kernel won't crash on access to memory that was freed.

Thanks
Tomas



  reply	other threads:[~2021-01-28  8:55 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-27 20:03 [PATCH] mtd: use refcount to prevent corruption Tomas Winkler
2021-01-27 20:03 ` Tomas Winkler
2021-01-27 20:46 ` Richard Weinberger
2021-01-27 20:46   ` Richard Weinberger
2021-01-27 20:55   ` Winkler, Tomas
2021-01-27 20:55     ` Winkler, Tomas
2021-01-27 21:17     ` Richard Weinberger
2021-01-27 21:17       ` Richard Weinberger
2021-01-28  6:33       ` Winkler, Tomas
2021-01-28  6:33         ` Winkler, Tomas
2021-01-28  7:47         ` Richard Weinberger
2021-01-28  7:47           ` Richard Weinberger
2021-01-28  8:53           ` Winkler, Tomas [this message]
2021-01-28  8:53             ` Winkler, Tomas
2021-01-28  9:00             ` Miquel Raynal
2021-01-28  9:00               ` Miquel Raynal
2021-01-28 17:57               ` Winkler, Tomas
2021-01-28 17:57                 ` Winkler, Tomas
2021-01-28 20:23                 ` Richard Weinberger
2021-01-28 20:23                   ` Richard Weinberger
2021-01-29 16:12                   ` Winkler, Tomas
2021-02-13 17:09                   ` Winkler, Tomas
2021-02-13 17:09                     ` Winkler, Tomas
2021-02-15 13:43                     ` Richard Weinberger
2021-02-15 13:43                       ` Richard Weinberger

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