linux-kernel - [PATCH] x86/alternatives: lockdep-enforce text_mutex in text

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Date:   Tue, 28 Aug 2018 08:55:14 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] x86/alternatives: lockdep-enforce text_mutex in
 text_poke*()

From: Jiri Kosina <jkosina@...e.cz>

text_poke() and text_poke_bp() must be called with text_mutex held.
Let's put proper lockdep anotation in place instead of just mentioning
the requirement in comment.

Reported-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Jiri Kosina <jkosina@...e.cz>
---
 arch/x86/kernel/alternative.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 014f214da581..b9d5e7c9ef43 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -684,8 +684,6 @@ void *__init_or_module text_poke_early(void *addr, const void *opcode,
  * 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: Must be called under text_mutex.
  */
 void *text_poke(void *addr, const void *opcode, size_t len)
 {
@@ -700,6 +698,8 @@ void *text_poke(void *addr, const void *opcode, size_t len)
 	 */
 	BUG_ON(!after_bootmem);
 
+	lockdep_assert_held(&text_mutex);
+
 	if (!core_kernel_text((unsigned long)addr)) {
 		pages[0] = vmalloc_to_page(addr);
 		pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
@@ -782,8 +782,6 @@ int poke_int3_handler(struct pt_regs *regs)
  *	- replace the first byte (int3) by the first byte of
  *	  replacing opcode
  *	- sync cores
- *
- * Note: must be called under text_mutex.
  */
 void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
 {
@@ -792,6 +790,9 @@ void *text_poke_bp(void *addr, const void *opcode, size_t len, void *handler)
 	bp_int3_handler = handler;
 	bp_int3_addr = (u8 *)addr + sizeof(int3);
 	bp_patching_in_progress = true;
+
+	lockdep_assert_held(&text_mutex);
+
 	/*
 	 * Corresponding read barrier in int3 notifier for making sure the
 	 * in_progress and handler are correctly ordered wrt. patching.

-- 
Jiri Kosina
SUSE Labs