vsprintf: Replace memory barrier with static_key for random_ptr_key update

[mirror_ubuntu-bionic-kernel.git] / lib / vsprintf.c

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 3dfa16c4581b01f0065208cb4179e7002047c8d2..0f21d58f4e66e3320ed84ec03bfa0a494f5d09dc 100644 (file)
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1660,19 +1660,22 @@ char *pointer_string(char *buf, char *end, const void *ptr,
        return number(buf, end, (unsigned long int)ptr, spec);
 }
 
-static bool have_filled_random_ptr_key __read_mostly;
+static DEFINE_STATIC_KEY_TRUE(not_filled_random_ptr_key);
 static siphash_key_t ptr_key __read_mostly;
 
-static void fill_random_ptr_key(struct random_ready_callback *unused)
+static void enable_ptr_key_workfn(struct work_struct *work)
 {
        get_random_bytes(&ptr_key, sizeof(ptr_key));
-       /*
-        * have_filled_random_ptr_key==true is dependent on get_random_bytes().
-        * ptr_to_id() needs to see have_filled_random_ptr_key==true
-        * after get_random_bytes() returns.
-        */
-       smp_mb();
-       WRITE_ONCE(have_filled_random_ptr_key, true);
+       /* Needs to run from preemptible context */
+       static_branch_disable(&not_filled_random_ptr_key);
+}
+
+static DECLARE_WORK(enable_ptr_key_work, enable_ptr_key_workfn);
+
+static void fill_random_ptr_key(struct random_ready_callback *unused)
+{
+       /* This may be in an interrupt handler. */
+       queue_work(system_unbound_wq, &enable_ptr_key_work);
 }
 
 static struct random_ready_callback random_ready = {
@@ -1686,7 +1689,8 @@ static int __init initialize_ptr_random(void)
        if (!ret) {
                return 0;
        } else if (ret == -EALREADY) {
-               fill_random_ptr_key(&random_ready);
+               /* This is in preemptible context */
+               enable_ptr_key_workfn(&enable_ptr_key_work);
                return 0;
        }
 
@@ -1700,7 +1704,7 @@ static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)
        unsigned long hashval;
        const int default_width = 2 * sizeof(ptr);
 
-       if (unlikely(!have_filled_random_ptr_key)) {
+       if (static_branch_unlikely(&not_filled_random_ptr_key)) {
                spec.field_width = default_width;
                /* string length must be less than default_width */
                return string(buf, end, "(ptrval)", spec);