[PATCH] net: liquidio: avoid sleeping allocation under octeon_devices_lock

[Yang Zi]

octeon_allocate_device() holds the spinlock octeon_devices_lock while
calling octeon_allocate_device_mem(), which uses vzalloc(). vzalloc()
can sleep, so this is a "scheduling while atomic" bug that can trigger a
sleeping-in-atomic warning (or deadlock on a preemptible kernel).

The memory allocation does not touch octeon_device[], octeon_device_count
or the free-slot search, so it does not need the lock. Move the
octeon_allocate_device_mem() call ahead of the lock: allocate the device
memory first, then take the lock only to find a free slot and register
the new device in the octeon_device[] array. If no slot is available
(all MAX_OCTEON_DEVICES slots in use), free the freshly allocated memory
and return NULL as before.

The lock therefore continues to protect exactly the data it documents:
the octeon_device[] array and octeon_device_count.

Signed-off-by: Yang Zi <2959243019@xxxxxx>
---
diff --git a/drivers/net/ethernet/cavium/liquidio/octeon_device.c b/drivers/net/ethernet/cavium/liquidio/octeon_device.c
index e98118e7b9fd..405ce14d46f5 100644
--- a/drivers/net/ethernet/cavium/liquidio/octeon_device.c
+++ b/drivers/net/ethernet/cavium/liquidio/octeon_device.c
@@ -723,6 +723,10 @@ struct octeon_device *octeon_allocate_device(u32 pci_id,
     u32 oct_idx = 0;
     struct octeon_device *oct = NULL;
 
+    oct = octeon_allocate_device_mem(pci_id, priv_size);
+    if (!oct)
+        return NULL;
+
     spin_lock(&octeon_devices_lock);
 
     for (oct_idx = 0; oct_idx < MAX_OCTEON_DEVICES; oct_idx++)
@@ -730,16 +734,16 @@ struct octeon_device *octeon_allocate_device(u32 pci_id,
             break;
 
     if (oct_idx < MAX_OCTEON_DEVICES) {
-        oct = octeon_allocate_device_mem(pci_id, priv_size);
-        if (oct) {
-            octeon_device_count++;
-            octeon_device[oct_idx] = oct;
-        }
+        octeon_device_count++;
+        octeon_device[oct_idx] = oct;
     }
 
     spin_unlock(&octeon_devices_lock);
-    if (!oct)
+
+    if (oct_idx == MAX_OCTEON_DEVICES) {
+        vfree(oct);
         return NULL;
+    }
 
     spin_lock_init(&oct->pci_win_lock);
     spin_lock_init(&oct->mem_access_lock);