Messages in this thread | | | Subject | Re: [PATCH 0/2] use DEFINE_DEBUGFS_ATTRIBUTE instead of DEFINE_SIMPLE_ATTRIBUTE | From | Lars-Peter Clausen <> | Date | Sun, 29 Mar 2020 15:46:17 +0200 |
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On 3/29/20 1:34 PM, Rohit Sarkar wrote: > On Sun, Mar 29, 2020 at 10:38:18AM +0100, Jonathan Cameron wrote: >> On Sat, 28 Mar 2020 12:04:53 +0530 >> Rohit Sarkar <rohitsarkar5398@gmail.com> wrote: >> >>> The debugfs_create_file_unsafe method does not protect the fops given to >>> it from file removal. It must be used with DEFINE_DEBUGFS_ATTRIBUTE >>> which makes the fops aware of the file lifetime. >>> >>> Further using DEFINE_DEBUGFS_ATTRIBUTE along with >>> debugfs_create_file_unsafe significantly reduces the overhead introduced by >>> debugfs_create_file which creates a lifetime managing proxy around each >>> fops handed in. Refer [1] for more on this. >>> >>> Fixes the following warnings reported by coccinelle: >>> drivers/iio/imu//adis16460.c:126:0-23: WARNING: adis16460_flash_count_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE >>> drivers/iio/imu//adis16460.c:108:0-23: WARNING: adis16460_product_id_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE >>> drivers/iio/imu//adis16460.c:90:0-23: WARNING: adis16460_serial_number_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE >>> drivers/iio/imu//adis16400.c:278:0-23: WARNING: adis16400_flash_count_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE >>> drivers/iio/imu//adis16400.c:261:0-23: WARNING: adis16400_product_id_fops should be defined with DEFINE_DEBUGFS_ATTRIBUTE >>> >>> [1]: https://lists.gt.net/linux/kernel/2369498 >>> >>> Rohit Sarkar (2): >>> iio: imu: adis16400: use DEFINE_DEBUGFS_ATTRIBUTE instead of >>> DEFINE_SIMPLE_ATTRIBUTE >>> iio: imu: adis16460: use DEFINE_DEBUGFS_ATTRIBUTE instead of >>> DEFINE_SIMPLE_ATTRIBUTE >>> >>> drivers/iio/imu/adis16400.c | 4 ++-- >>> drivers/iio/imu/adis16460.c | 6 +++--- >>> 2 files changed, 5 insertions(+), 5 deletions(-) >>> >> Hi Rohit, > Hey, >> You've opened a can of worms with this one. There as a previous series >> posted doing exactly this change back in 2019 by Zhong Jiang (cc'd) >> >> At the time I did a bit of looking into why this had been universally taken >> up cross tree and turned out there are some potential issues. >> >> Alexandru added it to the list of things to test, but I guess it got >> buried under other work and is still outstanding. >> >> https://lkml.org/lkml/2019/10/30/144 > Acc. to the patch by Zhong this change kind of comes off as a cosmetic > change as in the commit message he mentions "it is more clear". > > But there is certainly more to it than that: > In the current scenario since we are using debugfs_create_file_unsafe > the file has no protection whatsoever against removal.
The drivers you are patching all use debugfs_create_file() as far as I can see.
The way I understand it using DEFINE_DEBUGFS_ATTRIBUTE without switching to debugfs_create_file_unsafe() will not make a difference. There will only be more overhead since the files are protected twice.
- Lars
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