[PATCH v3 03/10] 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.

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