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Date: Thu, 30 Aug 2018 10:32:13 -0700 From: Nadav Amit <namit@...are.com> To: Thomas Gleixner <tglx@...utronix.de> CC: <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>, <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>, <linux-arch@...r.kernel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, Nadav Amit <namit@...are.com>, Andy Lutomirski <luto@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>, Kees Cook <keescook@...omium.org>, Dave Hansen <dave.hansen@...el.com> Subject: [PATCH 1/6] x86/alternatives: clarify text_mutex use in text_poke 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 <luto@...nel.org> Cc: Masami Hiramatsu <mhiramat@...nel.org> Cc: Kees Cook <keescook@...omium.org> Cc: Dave Hansen <dave.hansen@...el.com> Suggested-by: Peter Zijlstra <peterz@...radead.org> Signed-off-by: Nadav Amit <namit@...are.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
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