From: Jason Gunthorpe <jgg@ziepe.ca>
To: Lino Sanfilippo <l.sanfilippo@kunbus.com>
Cc: Lino Sanfilippo <LinoSanfilippo@gmx.de>,
peterhuewe@gmx.de, jarkko@kernel.org, stefanb@linux.vnet.ibm.com,
James.Bottomley@hansenpartnership.com, stable@vger.kernel.org,
linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/2] tpm: fix reference counting for struct tpm_chip
Date: Fri, 5 Feb 2021 11:58:08 -0400 [thread overview]
Message-ID: <20210205155808.GO4718@ziepe.ca> (raw)
In-Reply-To: <f6e5dd7d-30df-26d9-c712-677c127a8026@kunbus.com>
On Fri, Feb 05, 2021 at 04:50:13PM +0100, Lino Sanfilippo wrote:
>
> On 05.02.21 16:15, Jason Gunthorpe wrote:
> >
> > No, the cdev layer holds the refcount on the device while open is
> > being called.
> >
> Yes, but the reference that is responsible for the chip deallocation is chip->dev
> which is linked to chip->cdev and represents /dev/tpm, not /dev/tpmrm.
> You are right, we dont have the issue with /dev/tpm for the reason you mentioned.
> But /dev/tpmrm is represented by chip->cdevs and keeping this ref held by the cdev
> layer wont protect us from the chip being freed (which is the reason why we need
> the chip->dev reference in the first place).
No, they are all chained together because they are all in the same
struct:
struct tpm_chip {
struct device dev;
struct device devs;
struct cdev cdev;
struct cdev cdevs;
dev holds the refcount on memory, when it goes 0 the whole thing is
kfreed.
The rule is dev's refcount can't go to zero while any other refcount
is != 0.
For instance devs holds a get on dev that is put back only when devs
goes to 0:
static void tpm_devs_release(struct device *dev)
{
struct tpm_chip *chip = container_of(dev, struct tpm_chip, devs);
/* release the master device reference */
put_device(&chip->dev);
}
Both cdev elements do something similar inside the cdev layer.
The net result is during any open() the tpm_chip is guarenteed to have
a positive refcount.
Jason
next prev parent reply other threads:[~2021-02-05 23:42 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-04 23:50 [PATCH v3 0/2] TPM fixes Lino Sanfilippo
2021-02-04 23:50 ` [PATCH v3 1/2] tpm: fix reference counting for struct tpm_chip Lino Sanfilippo
2021-02-05 0:46 ` Stefan Berger
2021-02-05 1:44 ` Stefan Berger
2021-02-05 2:01 ` James Bottomley
2021-02-05 10:52 ` Lino Sanfilippo
2021-02-05 13:29 ` Stefan Berger
2021-02-05 10:34 ` Lino Sanfilippo
2021-02-05 6:50 ` Greg KH
2021-02-05 13:05 ` Jason Gunthorpe
2021-02-05 14:55 ` Lino Sanfilippo
2021-02-05 15:15 ` Jason Gunthorpe
2021-02-05 15:50 ` Lino Sanfilippo
2021-02-05 15:58 ` Jason Gunthorpe [this message]
2021-02-05 21:50 ` Lino Sanfilippo
2021-02-06 0:39 ` Jason Gunthorpe
2021-02-04 23:50 ` [PATCH v3 2/2] tpm: in tpm2_del_space check if ops pointer is still valid Lino Sanfilippo
2021-02-05 0:34 ` James Bottomley
2021-02-05 2:18 ` Jarkko Sakkinen
2021-02-05 16:48 ` James Bottomley
2021-02-05 17:25 ` Jason Gunthorpe
2021-02-05 17:54 ` James Bottomley
2021-02-06 1:02 ` Jason Gunthorpe
2021-02-06 1:08 ` James Bottomley
2021-02-06 1:34 ` Jason Gunthorpe
2021-02-09 11:52 ` Lino Sanfilippo
2021-02-09 13:36 ` Jason Gunthorpe
2021-02-09 13:39 ` Lino Sanfilippo
2021-02-12 11:02 ` Jarkko Sakkinen
2021-02-12 10:59 ` Jarkko Sakkinen
2021-02-14 17:22 ` Lino Sanfilippo
2021-02-05 10:30 ` Lino Sanfilippo
2021-03-06 16:07 ` Lino Sanfilippo
2021-02-05 6:51 ` Greg KH
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