[PATCH v4 03/10] mm/vmalloc: Support non-blocking GFP flags in alloc_vmap_area()

Uladzislau Rezki (Sony)
2025-10-07T12:20:50Z

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.

It is a preparation and adjustment step to later allow both GFP_ATOMIC
and GFP_NOWAIT allocations in this series.

Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
mm/vmalloc.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 798b2ed21e46..d83c01caaabe 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2017,6 +2017,7 @@ 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;

@@ -2028,7 +2029,8 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,

/* Only reclaim behaviour flags are relevant. */
gfp_mask = gfp_mask & GFP_RECLAIM_MASK;
- might_sleep();
+ allow_block = gfpflags_allow_blocking(gfp_mask);
+ might_sleep_if(allow_block);

/*
* If a VA is obtained from a global heap(if it fails here)
@@ -2062,7 +2064,8 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
* This is not a fast path. Check if yielding is needed. This
* is the only reschedule point in the vmalloc() path.
*/
- cond_resched();
+ if (allow_block)
+ cond_resched();
}

trace_alloc_vmap_area(addr, size, align, vstart, vend, IS_ERR_VALUE(addr));
@@ -2071,8 +2074,16 @@ 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))
- goto overflow;
+ if (IS_ERR_VALUE(addr)) {
+ if (allow_block)
+ goto overflow;
+
+ /*
+ * We can not trigger any reclaim logic because
+ * sleeping is not allowed, thus fail an allocation.
+ */
+ goto out_free_va;
+ }

va->va_start = addr;
va->va_end = addr + size;
@@ -2122,6 +2133,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
pr_warn("vmalloc_node_range for size %lu failed: Address range restricted to %#lx - %#lx\n",
size, vstart, vend);

+out_free_va:
kmem_cache_free(vmap_area_cachep, va);
return ERR_PTR(-EBUSY);
}
--
2.47.3