From 2c21fce80b6fab7304d2081f2b1157033e30ad50 Mon Sep 17 00:00:00 2001 From: Li Bin Date: Fri, 4 Dec 2015 11:38:40 +0800 Subject: [PATCH] UPSTREAM: arm64: ftrace: fix the comments for ftrace_modify_code There is no need to worry about module and __init text disappearing case, because that ftrace has a module notifier that is called when a module is being unloaded and before the text goes away and this code grabs the ftrace_lock mutex and removes the module functions from the ftrace list, such that it will no longer do any modifications to that module's text, the update to make functions be traced or not is done under the ftrace_lock mutex as well. And by now, __init section codes should not been modified by ftrace, because it is black listed in recordmcount.c and ignored by ftrace. Suggested-by: Steven Rostedt Signed-off-by: Li Bin Signed-off-by: Will Deacon Bug: 30369029 Patchset: arm64-ftrace (cherry picked from commit 004ab584e028093996cf5b8e220b8bc50c5111cf) Signed-off-by: Jeff Vander Stoep Change-Id: I69df7eddbf9e17031920b950312399dc4d36c09e --- arch/arm64/kernel/ftrace.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c index 9669b331a23b..8f7005bc35bd 100644 --- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -29,12 +29,11 @@ static int ftrace_modify_code(unsigned long pc, u32 old, u32 new, /* * Note: - * Due to modules and __init, code can disappear and change, - * we need to protect against faulting as well as code changing. - * We do this by aarch64_insn_*() which use the probe_kernel_*(). - * - * No lock is held here because all the modifications are run - * through stop_machine(). + * We are paranoid about modifying text, as if a bug were to happen, it + * could cause us to read or write to someplace that could cause harm. + * Carefully read and modify the code with aarch64_insn_*() which uses + * probe_kernel_*(), and make sure what we read is what we expected it + * to be before modifying it. */ if (validate) { if (aarch64_insn_read((void *)pc, &replaced)) -- 2.20.1