linux-kernel - Re: [PATCH v2] sched_ext: Use kvzalloc for large exit

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Message-ID: <Z_UI2AHtkIGS4bZR@gpd3>
Date: Tue, 8 Apr 2025 13:30:32 +0200
From: Andrea Righi <arighi@...dia.com>
To: Breno Leitao <leitao@...ian.org>
Cc: Tejun Heo <tj@...nel.org>, David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org, christophe.jaillet@...adoo.fr,
	kernel-team@...a.com, stable@...r.kernel.org,
	Rik van Riel <riel@...riel.com>
Subject: Re: [PATCH v2] sched_ext: Use kvzalloc for large exit_dump allocation

Hi Breno,

I already acked even the buggy version, so this one looks good. :)

On Tue, Apr 08, 2025 at 04:09:02AM -0700, Breno Leitao wrote:
> Replace kzalloc with kvzalloc for the exit_dump buffer allocation, which
> can require large contiguous memory (up to order=9) depending on the

BTW, from where this order=9 is coming from? exit_dump_len is 32K by
default, but a BPF scheduler can arbitrarily set it to any value via
ops->exit_dump_len, so it could be even bigger than an order 9 allocation.

Thanks,
-Andrea

> implementation. This change prevents allocation failures by allowing the
> system to fall back to vmalloc when contiguous memory allocation fails.
> 
> Since this buffer is only used for debugging purposes, physical memory
> contiguity is not required, making vmalloc a suitable alternative.
> 
> Cc: stable@...r.kernel.org
> Fixes: 07814a9439a3b0 ("sched_ext: Print debug dump after an error exit")
> Suggested-by: Rik van Riel <riel@...riel.com>
> Signed-off-by: Breno Leitao <leitao@...ian.org>
> Acked-by: Andrea Righi <arighi@...dia.com>
> ---
> Changes in v2:
> - Use kvfree() on the free path as well.
> - Link to v1: https://lore.kernel.org/r/20250407-scx-v1-1-774ba74a2c17@debian.org
> ---
>  kernel/sched/ext.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 66bcd40a28ca1..db9af6a3c04fd 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -4623,7 +4623,7 @@ static void scx_ops_bypass(bool bypass)
>  
>  static void free_exit_info(struct scx_exit_info *ei)
>  {
> -	kfree(ei->dump);
> +	kvfree(ei->dump);
>  	kfree(ei->msg);
>  	kfree(ei->bt);
>  	kfree(ei);
> @@ -4639,7 +4639,7 @@ static struct scx_exit_info *alloc_exit_info(size_t exit_dump_len)
>  
>  	ei->bt = kcalloc(SCX_EXIT_BT_LEN, sizeof(ei->bt[0]), GFP_KERNEL);
>  	ei->msg = kzalloc(SCX_EXIT_MSG_LEN, GFP_KERNEL);
> -	ei->dump = kzalloc(exit_dump_len, GFP_KERNEL);
> +	ei->dump = kvzalloc(exit_dump_len, GFP_KERNEL);
>  
>  	if (!ei->bt || !ei->msg || !ei->dump) {
>  		free_exit_info(ei);
> 
> ---
> base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
> change-id: 20250407-scx-11dbf94803c3
> 
> Best regards,
> -- 
> Breno Leitao <leitao@...ian.org>
>