From mboxrd@z Thu Jan 1 00:00:00 1970 From: huawei.libin@huawei.com (Li Bin) Date: Fri, 4 Dec 2015 11:23:45 +0800 Subject: [PATCH v2 2/2] arm64: ftrace: fix the comments for ftrace_modify_code In-Reply-To: <20151203215001.52fe192f@grimm.local.home> References: <1449195519-17901-1-git-send-email-huawei.libin@huawei.com> <1449195519-17901-3-git-send-email-huawei.libin@huawei.com> <20151203215001.52fe192f@grimm.local.home> Message-ID: <56610741.6060306@huawei.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org on 2015/12/4 10:50, Steven Rostedt wrote: > 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. Ok, I will modify it. Thanks, Li Bin > -- 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)) > > . >