text_mutex is expected to be held before text_poke() is called, but we
cannot add a lockdep assertion since kgdb does not take it, and instead
*supposedly* ensures the lock is not taken and will not be acquired by
any other core while text_poke() is running.
The reason for the "supposedly" comment is that it is not entirely clear
that this would be the case if gdb_do_roundup is zero.
Add a comment to clarify this behavior.
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Masami Hiramatsu <mhira...@kernel.org>
Cc: Kees Cook <keesc...@chromium.org>
Cc: Dave Hansen <dave.han...@intel.com>
Suggested-by: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Nadav Amit <na...@vmware.com>
---
arch/x86/kernel/alternative.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 014f214da581..d0c0d8b724e1 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -685,7 +685,10 @@ void *__init_or_module text_poke_early(void *addr, const
void *opcode,
* in a way that permits an atomic write. It also makes sure we fit on a single
* page.
*
- * Note: Must be called under text_mutex.
+ * Context: Must be called under text_mutex. kgdb is an exception: it does not
+ * hold the mutex, as it *supposedly* ensures that no other core is
+ * holding the mutex and ensures that none of them will acquire the
+ * mutex while the code runs.
*/
void *text_poke(void *addr, const void *opcode, size_t len)
{
--
2.17.1
