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

["Uladzislau Rezki (Sony)" <urezki@gmail.com>]

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