[PATCH v2] mm/vmalloc: clarify why vmap_range_noflush() might sleep

[PATCH v2] mm/vmalloc: clarify why vmap_range_noflush() might sleep

[Brendan Jackman]

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@google.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. */
 	might_sleep();
 	BUG_ON(addr >= end);
 

---
base-commit: ecc46e02e0abe025a6e840cba2d647f23fd1d721
change-id: 20251208-b4-vmalloc-might_alloc-754a791e4e10

Best regards,
-- 
Brendan Jackman <jackmanb@google.com>

Re: [PATCH v2] mm/vmalloc: clarify why vmap_range_noflush() might sleep

[Brendan Jackman]

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@google.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);