linux-kernel - Re: [PATCH v2] mm/vmalloc: clarify why vmap_range

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Message-ID: <DETH88RP5U4O.QACTRJIY5Y1X@google.com>
Date: Tue, 09 Dec 2025 06:36:51 +0000
From: Brendan Jackman <jackmanb@...gle.com>
To: Brendan Jackman <jackmanb@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Uladzislau Rezki <urezki@...il.com>
Cc: Anshuman Khandual <anshuman.khandual@....com>, <linux-mm@...ck.org>, 
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm/vmalloc: clarify why vmap_range_noflush() might sleep

On Tue Dec 9, 2025 at 5:44 AM UTC, Brendan Jackman wrote:
> The only reason vmap_range_noflush() can sleep is because of pagetable
> allocations.
>
> The actual allocation mechanism is arch-specific so might_alloc()
> doesn't work here (what GFP flags would be used?). Hence, just add a
> comment.
>
> Signed-off-by: Brendan Jackman <jackmanb@...gle.com>
> ---
> Changes in v2:
> - Switched from might_alloc() to keeping might_sleep() + comment
> - Link to v1: https://lore.kernel.org/r/20251208-b4-vmalloc-might_alloc-v1-1-94a9bb8ecb08@google.com
> ---
>  mm/vmalloc.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index a53c7462671bdd896f95712af71398ffbe22fb80..c23d378dd4446e2784505ec3d5bb9568fb0d3c9a 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -305,6 +305,7 @@ static int vmap_range_noflush(unsigned long addr, unsigned long end,
>  	int err;
>  	pgtbl_mod_mask mask = 0;
>  
> +	/* Might allocate pagetables. */

I just realised that for x86, there's also TLB shootdowns in
pud_free_pmd_page() etc. So I guess this is also a might_ for the the
lockdep_assert_irqs_enabled() in smp_call_function_many_cond(). Should
probably mention that too.

Anything else I missed, before I send v3?

>  	might_sleep();
>  	BUG_ON(addr >= end);