[v3,20/20] x86/alternative: Comment about module removal races

Commit Message

Edgecombe, Rick P Feb. 21, 2019, 11:44 p.m. UTC

From: Nadav Amit <[e-mail]>

Add a comment to clarify that users of text_poke() must ensure that
no races with module removal take place.

Cc: Masami Hiramatsu <[e-mail]>
Signed-off-by: Nadav Amit <[e-mail]>
Signed-off-by: Rick Edgecombe <[e-mail]>
---
 arch/x86/kernel/alternative.c | 5 +++++
 1 file changed, 5 insertions(+)

Patch

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index c63707e7ed3d..a1335b9486bf 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -809,6 +809,11 @@  static void *__text_poke(void *addr, const void *opcode, size_t len)
  * It means the size must be writable atomically and the address must be aligned
  * in a way that permits an atomic write. It also makes sure we fit on a single
  * page.
+ *
+ * Note that the caller must ensure that if the modified code is part of a
+ * module, the module would not be removed during poking. This can be achieved
+ * by registering a module notifier, and ordering module removal and patching
+ * trough a mutex.
  */
 void *text_poke(void *addr, const void *opcode, size_t len)
 {