Fix: lttng_kvmalloc helper NULL pointer OOPS

The static function __vmalloc_node is not visible by KALLSYMS_ALL on at
least some kernels, which leads to a call to a NULL function when trying
to perform allocation of lttng buffer memory under memory fragmentation
conditions (kmalloc_node failure).

Use __vmalloc_node_range instead, and check that the returned pointer
is non-NULL to ensure this type of failure does not happen in any
condition.

Fallback to __vmalloc(), even though it is not NUMA-aware, in case
we fail to find __vmalloc_node_range, and print an explicit warning
to the user console about the need to enable KALLSYMS_ALL.

This affects kernels < 4.12. Later kernels provide kvmalloc(), which
we use.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/wrapper/vmalloc.h b/wrapper/vmalloc.h
index e117584f37b6ae66a7ccae65dced8c061444d58e..b4d795404a2dfa454f9b1dae11a0f0d8963db6c9 100644 (file)
--- a/wrapper/vmalloc.h
+++ b/wrapper/vmalloc.h
@@ -107,32 +107,40 @@ void lttng_kvfree(const void *addr)
 
 #include <linux/slab.h>
 
+static inline
+void print_vmalloc_node_range_warning(void)
+{
+       printk_once(KERN_WARNING "LTTng: __vmalloc_node_range symbol lookup failed.\n");
+       printk_once(KERN_WARNING "Tracer performance will be degraded on NUMA systems.\n");
+       printk_once(KERN_WARNING "Please rebuild your kernel with CONFIG_KALLSYMS enabled.\n");
+}
+
 /*
  * kallsyms wrapper of __vmalloc_node with a fallback to kmalloc_node.
  */
 static inline
-void *__lttng_vmalloc_node_fallback(unsigned long size, unsigned long align,
-                         gfp_t gfp_mask, pgprot_t prot, int node, void *caller)
+void *__lttng_vmalloc_node_range(unsigned long size, unsigned long align,
+                       unsigned long start, unsigned long end, gfp_t gfp_mask,
+                       pgprot_t prot, unsigned long vm_flags, int node,
+                       const void *caller)
 {
-       void *ret;
-
 #ifdef CONFIG_KALLSYMS
        /*
-        * If we have KALLSYMS, get * __vmalloc_node which is not exported.
+        * If we have KALLSYMS, get * __vmalloc_node_range which is not exported.
         */
-       void *(*lttng__vmalloc_node)(unsigned long size, unsigned long align,
-                       gfp_t gfp_mask, pgprot_t prot, int node, void *caller);
-
-       lttng__vmalloc_node = (void *) kallsyms_lookup_funcptr("__vmalloc_node");
-       ret = lttng__vmalloc_node(size, align, gfp_mask, prot, node, caller);
-#else
-       /*
-        * If we don't have KALLSYMS, fallback to kmalloc_node.
-        */
-       ret = kmalloc_node(size, flags, node);
+       void *(*lttng__vmalloc_node_range)(unsigned long size, unsigned long align,
+                       unsigned long start, unsigned long end, gfp_t gfp_mask,
+                       pgprot_t prot, unsigned long vm_flags, int node,
+                       const void *caller);
+
+       lttng__vmalloc_node_range = (void *) kallsyms_lookup_funcptr("__vmalloc_node_range");
+       if (lttng__vmalloc_node_range)
+               return lttng__vmalloc_node_range(size, align, start, end, gfp_mask, prot,
+                               vm_flags, node, caller);
 #endif
-
-       return ret;
+       if (node != NUMA_NO_NODE)
+               print_vmalloc_node_range_warning();
+       return __vmalloc(size, gfp_mask, prot);
 }
 
 /**
@@ -170,23 +178,10 @@ void *lttng_kvmalloc_node(unsigned long size, gfp_t flags, int node)
         */
        ret = kmalloc_node(size, flags | __GFP_NOWARN | __GFP_NORETRY, node);
        if (!ret) {
-               if (node == NUMA_NO_NODE) {
-                       /*
-                        * If no node was specified, use __vmalloc which is
-                        * always exported.
-                        */
-                       ret = __vmalloc(size, flags | __GFP_HIGHMEM, PAGE_KERNEL);
-               } else {
-                       /*
-                        * Otherwise, we need to select a node but __vmalloc_node
-                        * is not exported, use this fallback wrapper which uses
-                        * kallsyms if available or falls back to kmalloc_node.
-                        */
-                       ret = __lttng_vmalloc_node_fallback(size, 1,
-                                       flags | __GFP_HIGHMEM, PAGE_KERNEL, node,
-                                       __builtin_return_address(0));
-               }
-
+               ret = __lttng_vmalloc_node_range(size, 1,
+                               VMALLOC_START, VMALLOC_END,
+                               flags | __GFP_HIGHMEM, PAGE_KERNEL, 0,
+                               node, __builtin_return_address(0));
                /*
                 * Make sure we don't trigger recursive page faults in the
                 * tracing fast path.