[RFC 2/7] mm/vmalloc: Support non-blocking GFP flags in alloc_vmap_area()

Uladzislau Rezki (Sony)
2025-07-04T15:25:48Z

alloc_vmap_area() currently assumes that sleeping is allowed during
allocation. This is not true for callers which pass non-blocking
GFP flags, such as GFP_ATOMIC or GFP_NOWAIT.

This patch adds logic to detect whether the given gfp_mask permits
blocking. It avoids invoking might_sleep() or falling back to reclaim
path if blocking is not allowed.

This makes alloc_vmap_area() safer for use in non-sleeping contexts,
where previously it could hit unexpected sleeps, trigger warnings.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
mm/vmalloc.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ab986dd09b6a..8c375b8e269d 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2009,6 +2009,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
unsigned long freed;
unsigned long addr;
unsigned int vn_id;
+ bool allow_block;
int purged = 0;
int ret;

@@ -2018,7 +2019,9 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
if (unlikely(!vmap_initialized))
return ERR_PTR(-EBUSY);

- might_sleep();
+ allow_block = gfpflags_allow_blocking(gfp_mask);
+ if (allow_block)
+ might_sleep();

/*
* If a VA is obtained from a global heap(if it fails here)
@@ -2030,7 +2033,8 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
*/
va = node_alloc(size, align, vstart, vend, &addr, &vn_id);
if (!va) {
- gfp_mask = gfp_mask & GFP_RECLAIM_MASK;
+ if (allow_block)
+ gfp_mask = gfp_mask & GFP_RECLAIM_MASK;

va = kmem_cache_alloc_node(vmap_area_cachep, gfp_mask, node);
if (unlikely(!va))
@@ -2057,8 +2061,14 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
* If an allocation fails, the error value is
* returned. Therefore trigger the overflow path.
*/
- if (IS_ERR_VALUE(addr))
+ if (IS_ERR_VALUE(addr)) {
+ if (!allow_block) {
+ kmem_cache_free(vmap_area_cachep, va);
+ return ERR_PTR(-ENOMEM);
+ }
+
goto overflow;
+ }

va->va_start = addr;
va->va_end = addr + size;
--
2.39.5