From: Wolfram Sang <wsa@the-dreams.de>
To: Peter Rosin <peda@axentia.se>
Cc: linux-kernel@vger.kernel.org, Peter Huewe <peterhuewe@gmx.de>,
Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
Jason Gunthorpe <jgg@ziepe.ca>, Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Brian Norris <computersforpeace@gmail.com>,
Gregory Fong <gregory.0xf0@gmail.com>,
Florian Fainelli <f.fainelli@gmail.com>,
bcm-kernel-feedback-list@broadcom.com,
Sekhar Nori <nsekhar@ti.com>, Kevin Hilman <khilman@kernel.org>,
Haavard Skinnemoen <hskinnemoen@gmail.com>,
Kukjin Kim <kgene@kernel.org>,
Krzysztof Kozlowski <krzk@kernel.org>,
Orson Zhai <orsonzhai@gmail.com>,
Baolin Wang <baolin.wang@linaro.org>,
Chunyan Zhang <zhang.lyra@gmail.com>,
Guenter Roeck <linux@roeck-us.net>, Crt Mori <cmo@melexis.com>,
Jonathan Cameron <jic23@kernel.org>,
Hartmut Knaack <knaack.h@gmx.de>,
Lars-Peter Clausen <lars@metafoo.de>,
Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
Dmitry Torokhov <dmitry.torokhov@gmail.com>,
Antti Palosaari <crope@iki.fi>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
Michael Krufky <mkrufky@linuxtv.org>,
Lee Jones <lee.jones@linaro.org>,
linux-integrity@vger.kernel.org, linux-i2c@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-samsung-soc@vger.kernel.org, linux-iio@vger.kernel.org,
linux-input@vger.kernel.org, linux-media@vger.kernel.org
Subject: Re: [PATCH v2 00/10] Split i2c_lock_adapter into i2c_lock_root and i2c_lock_segment
Date: Tue, 26 Jun 2018 11:37:36 +0900 [thread overview]
Message-ID: <20180626023735.xj7aqhvw7ta2lq6s@ninjato> (raw)
In-Reply-To: <20180620051803.12206-1-peda@axentia.se>
On Wed, Jun 20, 2018 at 07:17:53AM +0200, Peter Rosin wrote:
> Hi!
>
> With the introduction of mux-locked I2C muxes, the concept of
> locking only a segment of the I2C adapter tree was added. At the
> time, I did not want to cause a lot of extra churn, so left most
> users of i2c_lock_adapter alone and apparently didn't think enough
> about it; they simply continued to lock the whole adapter tree.
> However, i2c_lock_adapter is in fact wrong for almost every caller
> (there is naturally an exception) that is itself not a driver for
> a root adapter. What normal drivers generally want is to only
> lock the segment of the adapter tree that their device sits on.
>
> In fact, if a device sits behind a mux-locked I2C mux, and its
> driver calls i2c_lock_adapter followed by an unlocked I2C transfer,
> things will deadlock (since even a mux-locked I2C adapter will lock
> its parent at some point). If the device is not sitting behind a
> mux-locked I2C mux (i.e. either directly on the root adapter or
> behind a (chain of) parent-locked I2C muxes) the root/segment
> distinction is of no consequence; the root adapter is locked either
> way.
>
> Mux-locked I2C muxes are probably not that common, and putting any
> of the affected devices behind one is probably even rarer, which
> is why we have not seen any deadlocks. At least not that I know
> of...
>
> Since silently changing the semantics of i2c_lock_adapter might
> be quite a surprise, especially for out-of-tree users, this series
> instead removes the function and forces all users to explicitly
> name I2C_LOCK_SEGMENT or I2C_LOCK_ROOT_ADAPTER in a call to
> i2c_lock_bus, as suggested by Wolfram. Yes, users will be a teensy
> bit more wordy, but open-coding I2C locking from random drivers
> should be avoided, so it's perhaps a good thing if it doesn't look
> too neat?
>
> I suggest that Wolfram takes this series through the I2C tree and
> creates an immutable branch for the other subsystems. The series
> is based on v4.18-r1.
Applied to a seperate branch named "i2c/precise-locking-names" which I
will merge into for-next, so it will get proper testing already. Once we
get the missing acks from media, MFD, and IIO maintainers, I will merge
it into for-4.19.
Thank you, Peter!
WARNING: multiple messages have this Message-ID (diff)
From: Wolfram Sang <wsa@the-dreams.de>
To: Peter Rosin <peda@axentia.se>
Cc: linux-kernel@vger.kernel.org, Peter Huewe <peterhuewe@gmx.de>,
Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
Jason Gunthorpe <jgg@ziepe.ca>, Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Brian Norris <computersforpeace@gmail.com>,
Gregory Fong <gregory.0xf0@gmail.com>,
Florian Fainelli <f.fainelli@gmail.com>,
bcm-kernel-feedback-list@broadcom.com,
Sekhar Nori <nsekhar@ti.com>, Kevin Hilman <khilman@kernel.org>,
Haavard Skinnemoen <hskinnemoen@gmail.com>,
Kukjin Kim <kgene@kernel.org>,
Krzysztof Kozlowski <krzk@kernel.org>,
Orson Zhai <orsonzhai@gmail.com>,
Baolin Wang <baolin.wang@linaro.org>,
Chunyan Zhang <zhang.lyra@gmail.com>,
Guenter Roeck <linux@roeck-us.net>, Crt Mori <cmo@melexis.com>
Subject: Re: [PATCH v2 00/10] Split i2c_lock_adapter into i2c_lock_root and i2c_lock_segment
Date: Tue, 26 Jun 2018 11:37:36 +0900 [thread overview]
Message-ID: <20180626023735.xj7aqhvw7ta2lq6s@ninjato> (raw)
In-Reply-To: <20180620051803.12206-1-peda@axentia.se>
On Wed, Jun 20, 2018 at 07:17:53AM +0200, Peter Rosin wrote:
> Hi!
>
> With the introduction of mux-locked I2C muxes, the concept of
> locking only a segment of the I2C adapter tree was added. At the
> time, I did not want to cause a lot of extra churn, so left most
> users of i2c_lock_adapter alone and apparently didn't think enough
> about it; they simply continued to lock the whole adapter tree.
> However, i2c_lock_adapter is in fact wrong for almost every caller
> (there is naturally an exception) that is itself not a driver for
> a root adapter. What normal drivers generally want is to only
> lock the segment of the adapter tree that their device sits on.
>
> In fact, if a device sits behind a mux-locked I2C mux, and its
> driver calls i2c_lock_adapter followed by an unlocked I2C transfer,
> things will deadlock (since even a mux-locked I2C adapter will lock
> its parent at some point). If the device is not sitting behind a
> mux-locked I2C mux (i.e. either directly on the root adapter or
> behind a (chain of) parent-locked I2C muxes) the root/segment
> distinction is of no consequence; the root adapter is locked either
> way.
>
> Mux-locked I2C muxes are probably not that common, and putting any
> of the affected devices behind one is probably even rarer, which
> is why we have not seen any deadlocks. At least not that I know
> of...
>
> Since silently changing the semantics of i2c_lock_adapter might
> be quite a surprise, especially for out-of-tree users, this series
> instead removes the function and forces all users to explicitly
> name I2C_LOCK_SEGMENT or I2C_LOCK_ROOT_ADAPTER in a call to
> i2c_lock_bus, as suggested by Wolfram. Yes, users will be a teensy
> bit more wordy, but open-coding I2C locking from random drivers
> should be avoided, so it's perhaps a good thing if it doesn't look
> too neat?
>
> I suggest that Wolfram takes this series through the I2C tree and
> creates an immutable branch for the other subsystems. The series
> is based on v4.18-r1.
Applied to a seperate branch named "i2c/precise-locking-names" which I
will merge into for-next, so it will get proper testing already. Once we
get the missing acks from media, MFD, and IIO maintainers, I will merge
it into for-4.19.
Thank you, Peter!
WARNING: multiple messages have this Message-ID (diff)
From: wsa@the-dreams.de (Wolfram Sang)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2 00/10] Split i2c_lock_adapter into i2c_lock_root and i2c_lock_segment
Date: Tue, 26 Jun 2018 11:37:36 +0900 [thread overview]
Message-ID: <20180626023735.xj7aqhvw7ta2lq6s@ninjato> (raw)
In-Reply-To: <20180620051803.12206-1-peda@axentia.se>
On Wed, Jun 20, 2018 at 07:17:53AM +0200, Peter Rosin wrote:
> Hi!
>
> With the introduction of mux-locked I2C muxes, the concept of
> locking only a segment of the I2C adapter tree was added. At the
> time, I did not want to cause a lot of extra churn, so left most
> users of i2c_lock_adapter alone and apparently didn't think enough
> about it; they simply continued to lock the whole adapter tree.
> However, i2c_lock_adapter is in fact wrong for almost every caller
> (there is naturally an exception) that is itself not a driver for
> a root adapter. What normal drivers generally want is to only
> lock the segment of the adapter tree that their device sits on.
>
> In fact, if a device sits behind a mux-locked I2C mux, and its
> driver calls i2c_lock_adapter followed by an unlocked I2C transfer,
> things will deadlock (since even a mux-locked I2C adapter will lock
> its parent at some point). If the device is not sitting behind a
> mux-locked I2C mux (i.e. either directly on the root adapter or
> behind a (chain of) parent-locked I2C muxes) the root/segment
> distinction is of no consequence; the root adapter is locked either
> way.
>
> Mux-locked I2C muxes are probably not that common, and putting any
> of the affected devices behind one is probably even rarer, which
> is why we have not seen any deadlocks. At least not that I know
> of...
>
> Since silently changing the semantics of i2c_lock_adapter might
> be quite a surprise, especially for out-of-tree users, this series
> instead removes the function and forces all users to explicitly
> name I2C_LOCK_SEGMENT or I2C_LOCK_ROOT_ADAPTER in a call to
> i2c_lock_bus, as suggested by Wolfram. Yes, users will be a teensy
> bit more wordy, but open-coding I2C locking from random drivers
> should be avoided, so it's perhaps a good thing if it doesn't look
> too neat?
>
> I suggest that Wolfram takes this series through the I2C tree and
> creates an immutable branch for the other subsystems. The series
> is based on v4.18-r1.
Applied to a seperate branch named "i2c/precise-locking-names" which I
will merge into for-next, so it will get proper testing already. Once we
get the missing acks from media, MFD, and IIO maintainers, I will merge
it into for-4.19.
Thank you, Peter!
next prev parent reply other threads:[~2018-06-26 2:37 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-20 5:17 [PATCH v2 00/10] Split i2c_lock_adapter into i2c_lock_root and i2c_lock_segment Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 5:17 ` [PATCH v2 01/10] tpm/tpm_i2c_infineon: switch to i2c_lock_bus(..., I2C_LOCK_SEGMENT) Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-25 10:24 ` Jarkko Sakkinen
2018-06-25 10:24 ` Jarkko Sakkinen
2018-06-25 10:24 ` Jarkko Sakkinen
2018-06-26 10:07 ` Alexander Steffen
2018-06-26 10:07 ` Alexander Steffen
2018-06-26 10:07 ` Alexander Steffen
2018-06-26 12:05 ` Jarkko Sakkinen
2018-06-26 12:05 ` Jarkko Sakkinen
2018-06-26 12:05 ` Jarkko Sakkinen
2018-06-26 12:05 ` Jarkko Sakkinen
2018-06-26 12:07 ` Jarkko Sakkinen
2018-06-26 12:07 ` Jarkko Sakkinen
2018-06-26 12:07 ` Jarkko Sakkinen
2018-06-26 12:07 ` Jarkko Sakkinen
2018-06-20 5:17 ` [PATCH v2 02/10] i2c: mux: pca9541: " Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 5:17 ` [PATCH v2 03/10] input: rohm_bu21023: " Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 20:28 ` Dmitry Torokhov
2018-06-20 20:28 ` Dmitry Torokhov
2018-06-20 20:28 ` Dmitry Torokhov
2018-06-20 5:17 ` [PATCH v2 04/10] media: af9013: " Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 5:17 ` [PATCH v2 05/10] media: drxk_hard: " Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 5:17 ` [PATCH v2 06/10] media: rtl2830: " Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 5:17 ` Peter Rosin
2018-06-20 5:18 ` [PATCH v2 07/10] media: tda1004x: " Peter Rosin
2018-06-20 5:18 ` Peter Rosin
2018-06-20 5:18 ` Peter Rosin
2018-06-20 5:18 ` [PATCH v2 08/10] media: tda18271: " Peter Rosin
2018-06-20 5:18 ` Peter Rosin
2018-06-20 5:18 ` Peter Rosin
2018-06-20 5:18 ` [PATCH v2 09/10] mfd: 88pm860x-i2c: " Peter Rosin
2018-06-20 5:18 ` Peter Rosin
2018-06-20 5:18 ` Peter Rosin
2018-07-04 7:04 ` Lee Jones
2018-07-04 7:04 ` Lee Jones
2018-07-04 7:04 ` Lee Jones
2018-07-04 7:04 ` Lee Jones
2018-06-20 5:18 ` [PATCH v2 10/10] i2c: remove i2c_lock_adapter and use i2c_lock_bus directly Peter Rosin
2018-06-20 5:18 ` Peter Rosin
2018-06-20 5:18 ` Peter Rosin
2018-06-26 8:28 ` Jonathan Cameron
2018-06-26 8:28 ` Jonathan Cameron
2018-06-26 8:28 ` Jonathan Cameron
2018-06-26 14:09 ` Sekhar Nori
2018-06-26 14:09 ` Sekhar Nori
2018-06-26 14:09 ` Sekhar Nori
2018-06-26 2:37 ` Wolfram Sang [this message]
2018-06-26 2:37 ` [PATCH v2 00/10] Split i2c_lock_adapter into i2c_lock_root and i2c_lock_segment Wolfram Sang
2018-06-26 2:37 ` Wolfram Sang
2018-07-12 21:28 ` Wolfram Sang
2018-07-12 21:28 ` Wolfram Sang
2018-07-12 21:28 ` Wolfram Sang
2018-07-12 21:28 ` Wolfram Sang
2018-07-12 21:59 ` Mauro Carvalho Chehab
2018-07-12 21:59 ` Mauro Carvalho Chehab
2018-07-12 21:59 ` Mauro Carvalho Chehab
2018-07-12 22:11 ` Wolfram Sang
2018-07-12 22:11 ` Wolfram Sang
2018-07-12 22:11 ` Wolfram Sang
2018-07-12 22:11 ` Wolfram Sang
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