linux-kernel - Re: [PATCH] mm,page

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Date: Fri, 15 Mar 2024 14:07:45 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Oscar Salvador <osalvador@...e.de>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Michal Hocko <mhocko@...e.com>, Marco Elver <elver@...gle.com>,
 Andrey Konovalov <andreyknvl@...il.com>,
 Alexander Potapenko <glider@...gle.com>
Subject: Re: [PATCH] mm,page_owner: Fix recursion

On 3/14/24 00:42, Oscar Salvador wrote:
> Prior to 217b2119b9e2 ("mm,page_owner: implement the tracking of the stacks count")
> the only place where page_owner could potentially go into recursion due to
> its need of allocating more memory was in save_stack(), which ends up calling
> into stackdepot code with the possibility of allocating memory.
> 
> We made sure to guard against that by signaling that the current task was
> already in page_owner code, so in case a recursion attempt was made, we
> could catch that and return dummy_handle.
> 
> After above commit, a new place in page_owner code was introduced where we
> could allocate memory, meaning we could go into recursion would we take that
> path.
> 
> Make sure to signal that we are in page_owner in that codepath as well.
> Move the guard code into two helpers {un}set_current_in_page_owner()
> and use them prior to calling in the two functions that might allocate
> memory.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> Fixes: 217b2119b9e2 ("mm,page_owner: implement the tracking of the stacks count")
> ---
>  mm/page_owner.c | 30 +++++++++++++++++++++---------
>  1 file changed, 21 insertions(+), 9 deletions(-)
> 
> @@ -292,7 +302,9 @@ noinline void __set_page_owner(struct page *page, unsigned short order,
>  		return;
>  	__set_page_owner_handle(page_ext, handle, order, gfp_mask);
>  	page_ext_put(page_ext);
> +	set_current_in_page_owner();
>  	inc_stack_record_count(handle, gfp_mask);
> +	unset_current_in_page_owner();

This is because of the kmalloc() in add_stack_record_to_list() right? Why
not wrap just that then?

>  }
>  
>  void __set_page_owner_migrate_reason(struct page *page, int reason)