From mboxrd@z Thu Jan 1 00:00:00 1970 From: rostedt@goodmis.org (Steven Rostedt) Date: Thu, 3 Dec 2015 21:50:01 -0500 Subject: [PATCH v2 2/2] arm64: ftrace: fix the comments for ftrace_modify_code In-Reply-To: <1449195519-17901-3-git-send-email-huawei.libin@huawei.com> References: <1449195519-17901-1-git-send-email-huawei.libin@huawei.com> <1449195519-17901-3-git-send-email-huawei.libin@huawei.com> Message-ID: <20151203215001.52fe192f@grimm.local.home> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, 4 Dec 2015 10:18:39 +0800 Li Bin wrote: > There is no need to worry about module 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. > > Signed-off-by: Li Bin > --- > arch/arm64/kernel/ftrace.c | 5 +---- > 1 files changed, 1 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c > index 9669b33..ee91c0c 100644 > --- a/arch/arm64/kernel/ftrace.c > +++ b/arch/arm64/kernel/ftrace.c > @@ -29,12 +29,9 @@ static int ftrace_modify_code(unsigned long pc, u32 old, u32 new, > > /* > * Note: > - * Due to modules and __init, code can disappear and change, > + * Due to __init, code can disappear and change, Init code should not be modified either because it is black listed in recordmcount.c. I say just change the comment to be something like: 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. -- Steve > * 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(). > */ > if (validate) { > if (aarch64_insn_read((void *)pc, &replaced))