tracing/user_events: Use alloc_pages instead of kzalloc() for register pages

kzalloc virtual addresses do not work with SetPageReserved, use the actual
page virtual addresses instead via alloc_pages.

The issue is reported when booting with user_events and
DEBUG_VM_PGFLAGS=y.

Also make the number of events based on the ORDER.

Link: https://lore.kernel.org/all/CADYN=9+xY5Vku3Ws5E9S60SM5dCFfeGeRBkmDFbcxX0ZMoFing@mail.gmail.com/
Link: https://lore.kernel.org/all/20220311223028.1865-1-beaub@linux.microsoft.com/
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Reported-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index 4febc1d..e10ad05 100644 (file)
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -30,9 +30,10 @@
 
 /*
  * Limits how many trace_event calls user processes can create:
- * Must be multiple of PAGE_SIZE.
+ * Must be a power of two of PAGE_SIZE.
  */
-#define MAX_PAGES 1
+#define MAX_PAGE_ORDER 0
+#define MAX_PAGES (1 << MAX_PAGE_ORDER)
 #define MAX_EVENTS (MAX_PAGES * PAGE_SIZE)
 
 /* Limit how long of an event name plus args within the subsystem. */
@@ -1622,16 +1623,17 @@ static void set_page_reservations(bool set)
 
 static int __init trace_events_user_init(void)
 {
+       struct page *pages;
        int ret;
 
        /* Zero all bits beside 0 (which is reserved for failures) */
        bitmap_zero(page_bitmap, MAX_EVENTS);
        set_bit(0, page_bitmap);
 
-       register_page_data = kzalloc(MAX_EVENTS, GFP_KERNEL);
-
-       if (!register_page_data)
+       pages = alloc_pages(GFP_KERNEL | __GFP_ZERO, MAX_PAGE_ORDER);
+       if (!pages)
                return -ENOMEM;
+       register_page_data = page_address(pages);
 
        set_page_reservations(true);
 
@@ -1640,7 +1642,7 @@ static int __init trace_events_user_init(void)
        if (ret) {
                pr_warn("user_events could not register with tracefs\n");
                set_page_reservations(false);
-               kfree(register_page_data);
+               __free_pages(pages, MAX_PAGE_ORDER);
                return ret;
        }