Re: [PATCH mm-hotfixes-unstable] mm/damon/sysfs: fix wrong empty schemes assumption under online tuning in damon_sysfs_set_schemes()

[SeongJae Park]

On Tue, 22 Nov 2022 19:53:33 +0000 SeongJae Park <sj@xxxxxxxxxx> wrote:

> Hi Andrew,
> 
> On Tue, 22 Nov 2022 19:48:31 +0000 SeongJae Park <sj@xxxxxxxxxx> wrote:
> 
> > Commit da87878010e5 ("mm/damon/sysfs: support online inputs update")
> > made 'damon_sysfs_set_schemes()' to be called for running DAMON context,
> > which could have schemes.  In the case, DAMON sysfs interface is
> > supposed to update, remove, or add schemes to reflect the sysfs files.
> > However, the code is assuming the DAMON context wouldn't have schemes at
> > all, and therefore creates and adds new schemes.  As a result, the code
> > doesn't work as intended for online schemes tuning and could have more
> > than expected memory footprint.   The schemes are all in the DAMON
> > context, so it doesn't leak the memory, though.
> > 
> > Remove the wrong asssumption (the DAMON context wouldn't have schemes)
> > in 'damon_sysfs_set_schemes()' to fix the bug.
> > 
> > Fixes: da87878010e5 ("mm/damon/sysfs: support online inputs update")
> > Cc: <stable@xxxxxxxxxxxxxxx> # 5.19.y
> > Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
> 
> This patch is for a hotfix, so based on mm-hotfixes-unstable.  And this makes a
> following sysfs refactoring patch, "mm/damon/sysfs: split out schemes directory
> implementation to separate file" conflicts.  Below is the conflict resolved
> version of the patch.  Please replace it with below one.  Sorry for the
> inconvenience and thank you for your help in advance!
> 
> ================================ 8< ===========================================
> 
> From bfb5e978a34626f5b19ee777eeb3187323e6a546 Mon Sep 17 00:00:00 2001
> From: SeongJae Park <sj@xxxxxxxxxx>
> Date: Wed, 26 Oct 2022 22:59:41 +0000
> Subject: [PATCH mm-unstable] mm/damon/sysfs: split out schemes directory implementation to
>  separate file
> 
> DAMON sysfs interface for 'schemes' directory is implemented using about
> one thousand lines of code.  It has no strong dependency with other
> parts of its file, so split it out to another file for better code
> management.
> 
> Link: https://lkml.kernel.org/r/20221026225943.100429-11-sj@xxxxxxxxxx
> Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> ---
>  mm/damon/Makefile        |    2 +-
>  mm/damon/sysfs-common.h  |   22 +
>  mm/damon/sysfs-schemes.c | 1068 ++++++++++++++++++++++++++++++++++++++
>  mm/damon/sysfs.c         | 1064 -------------------------------------
>  4 files changed, 1091 insertions(+), 1065 deletions(-)
>  create mode 100644 mm/damon/sysfs-schemes.c
> 
[...]
> diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
> new file mode 100644
> index 000000000000..731a2314623c
> --- /dev/null
> +++ b/mm/damon/sysfs-schemes.c
[...]
> +static int damon_sysfs_set_schemes(struct damon_ctx *ctx,
> +		struct damon_sysfs_schemes *sysfs_schemes)

Sorry, I made a mistake.  This should be not static.  Below is the fixed
version of the patch.

================================= 8< ==========================================