linux-kernel - Re: [PATCH v7 1/1] kasan: Avoid sleepable page allocation from atomic context

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Message-ID: <aCIiYgeQcvO+VQzy@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com>
Date: Mon, 12 May 2025 18:31:30 +0200
From: Alexander Gordeev <agordeev@...ux.ibm.com>
To: Harry Yoo <harry.yoo@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Daniel Axtens <dja@...ens.net>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, kasan-dev@...glegroups.com,
        linux-s390@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v7 1/1] kasan: Avoid sleepable page allocation from
 atomic context

On Tue, May 13, 2025 at 12:33:35AM +0900, Harry Yoo wrote:
> Thanks for the update, but I don't think nr_populated is sufficient
> here. If nr_populated in the last iteration is smaller than its value
> in any previous iteration, it could lead to a memory leak.
> 
> That's why I suggested (PAGE_SIZE / sizeof(data.pages[0])).
> ...but on second thought maybe touching the whole array is not
> efficient either.

Yes, I did not like it and wanted to limit the number of pages,
but did not realize that using nr_populated still could produce
leaks. In addition I could simply do:

	max_populted = max(max_populted, nr_populated);
	...
	free_pages_bulk(data.pages, max_populated);

> If this ends up making things complicated probably we should just
> merge v6 instead (v6 looks good)? micro-optimizing vmalloc shadow memory
> population doesn't seem worth it if it comes at the cost of complexity :)

v6 is okay, except that in v7 I use break instead of return:

	ret = apply_to_page_range(...);
	if (ret)
		break;

and as result can call the final:

	free_page((unsigned long)data.pages);

Frankly, I do not have strong opinion.

> -- 
> Cheers,
> Harry / Hyeonggon

Thanks!