Logan Gunthorpe 233ed09d7f chardev: add helper function to register char devs with a struct device ... Credit for this patch goes is shared with Dan Williams [1]. I've taken things one step further to make the helper function more useful and clean up calling code. There's a common pattern in the kernel whereby a struct cdev is placed in a structure along side a struct device which manages the life-cycle of both. In the naive approach, the reference counting is broken and the struct device can free everything before the chardev code is entirely released. Many developers have solved this problem by linking the internal kobjs in this fashion: cdev.kobj.parent = &parent_dev.kobj; The cdev code explicitly gets and puts a reference to it's kobj parent. So this seems like it was intended to be used this way. Dmitrty Torokhov first put this in place in 2012 with this commit: 2f0157f char_dev: pin parent kobject and the first instance of the fix was then done in the input subsystem in the following commit: 4a215aa Input: fix use-after-free introduced with dynamic minor changes Subsequently over the years, however, this issue seems to have tripped up multiple developers independently. For example, see these commits: 0d5b7da iio: Prevent race between IIO chardev opening and IIO device (by Lars-Peter Clausen in 2013) ba0ef85 tpm: Fix initialization of the cdev (by Jason Gunthorpe in 2015) 5b28dde [media] media: fix use-after-free in cdev_put() when app exits after driver unbind (by Shauh Khan in 2016) This technique is similarly done in at least 15 places within the kernel and probably should have been done so in another, at least, 5 places. The kobj line also looks very suspect in that one would not expect drivers to have to mess with kobject internals in this way. Even highly experienced kernel developers can be surprised by this code, as seen in [2]. To help alleviate this situation, and hopefully prevent future wasted effort on this problem, this patch introduces a helper function to register a char device along with its parent struct device. This creates a more regular API for tying a char device to its parent without the developer having to set members in the underlying kobject. This patch introduce cdev_device_add and cdev_device_del which replaces a common pattern including setting the kobj parent, calling cdev_add and then calling device_add. It also introduces cdev_set_parent for the few cases that set the kobject parent without using device_add. [1] https://lkml.org/lkml/2017/2/13/700 [2] https://lkml.org/lkml/2017/2/10/370 Signed-off-by: Logan Gunthorpe <logang@deltatee.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Reviewed-by: Hans Verkuil <hans.verkuil@cisco.com> Reviewed-by: Alexandre Belloni <alexandre.belloni@free-electrons.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2017-03-21 06:44:32 +01:00
..
acpi	Merge branches 'acpi-bus', 'acpi-sleep' and 'acpi-processor'	2017-02-20 14:28:03 +01:00
asm-generic	mm: convert generic code to 5-level paging	2017-03-09 11:48:47 -08:00
clocksource
crypto	crypto: api - Add crypto_requires_off helper	2017-02-27 18:09:39 +08:00
drm	sched/headers: Prepare to remove the <linux/mm_types.h> dependency from <linux/sched.h>	2017-03-02 08:42:37 +01:00
dt-bindings	scripts/spelling.txt: add "overide" pattern and fix typo instances	2017-03-09 17:01:09 -08:00
keys	KEYS: Differentiate uses of rcu_dereference_key() and user_key_payload()	2017-03-02 10:09:00 +11:00
kvm
linux	chardev: add helper function to register char devs with a struct device	2017-03-21 06:44:32 +01:00
math-emu
media	media fixes for v4.11-rc2	2017-03-09 15:50:56 -08:00
memory
misc	auxdisplay: charlcd: Add support for 4-bit interfaces	2017-03-17 15:10:49 +09:00
net	scripts/spelling.txt: add "overide" pattern and fix typo instances	2017-03-09 17:01:09 -08:00
pcmcia
ras
rdma	sched/headers: Prepare to remove <linux/cred.h> inclusion from <linux/sched.h>	2017-03-02 08:42:31 +01:00
rxrpc
scsi	scsi: remove scsi_execute_req_flags	2017-02-23 16:57:36 -05:00
soc	ARC updates for 4.11 rc1	2017-02-22 10:33:53 -08:00
sound	sched/headers: Prepare to remove spurious <linux/sched.h> inclusion dependencies	2017-03-02 08:42:41 +01:00
target	Merge branch 'WIP.sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip	2017-03-03 10:16:38 -08:00
trace	There was some breakage with the changes for jump labels in the 4.11 merge	2017-03-07 09:37:28 -08:00
uapi	pps: fix padding issue with PPS_FETCH for ioctl_compat	2017-03-17 15:10:49 +09:00
video
xen	Merge branch 'stable/for-linus-4.11' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/swiotlb	2017-03-07 10:23:17 -08:00
Kbuild