On 2015/3/4 11:36, Masami Hiramatsu wrote: > (2015/03/04 11:24), Wang Nan wrote: >> On 2015/3/4 1:06, Petr Mladek wrote: >>> On Tue 2015-03-03 13:09:05, Wang Nan wrote: >>>> Before ftrace convertin instruction to nop, if an early kprobe is >>>> registered then unregistered, without this patch its first bytes will >>>> be replaced by head of NOP, which may confuse ftrace. >>>> >>>> Actually, since we have a patch which convert ftrace entry to nop >>>> when probing, this problem should never be triggered. Provide it for >>>> safety. >>>> >>>> Signed-off-by: Wang Nan <wangn...@huawei.com> >>>> --- >>>> arch/x86/kernel/kprobes/core.c | 3 +++ >>>> 1 file changed, 3 insertions(+) >>>> >>>> diff --git a/arch/x86/kernel/kprobes/core.c >>>> b/arch/x86/kernel/kprobes/core.c >>>> index 87beb64..c7d304d 100644 >>>> --- a/arch/x86/kernel/kprobes/core.c >>>> +++ b/arch/x86/kernel/kprobes/core.c >>>> @@ -225,6 +225,9 @@ __recover_probed_insn(kprobe_opcode_t *buf, unsigned >>>> long addr) >>>> struct kprobe *kp; >>>> unsigned long faddr; >>>> >>>> + if (!kprobes_on_ftrace_initialized) >>>> + return addr; >>> >>> This is not correct. The function has to return a buffer with the original >>> code also when it is modified by normal kprobes. If it is a normal >>> Kprobe, it reads the current code and replaces the first byte (INT3 >>> instruction) with the saved kp->opcode. >>> >>>> + >>>> kp = get_kprobe((void *)addr); >>>> faddr = ftrace_location(addr); >>> >>> IMHO, the proper fix might be to replace the above line with >>> >>> if (kprobes_on_ftrace_initialized) >>> faddr = ftrace_location(addr); >>> else >>> faddr = 0UL; >>> >>> By other words, it might pretend that it is not a ftrace location >>> when the ftrace is not ready yet. >>> >> >> Thanks for your reply. I'll follow your suggection in my next version. I >> change >> it as follow to enable the checking. >> >> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c >> index 4e3d5a9..3241677 100644 >> --- a/arch/x86/kernel/kprobes/core.c >> +++ b/arch/x86/kernel/kprobes/core.c >> @@ -234,6 +234,20 @@ __recover_probed_insn(kprobe_opcode_t *buf, unsigned >> long addr) >> */ >> if (WARN_ON(faddr && faddr != addr)) >> return 0UL; >> + >> + /* >> + * If ftrace is not ready yet, pretend this is not an ftrace >> + * location, because currently the target instruction has not >> + * been replaced by a NOP yet. When ftrace trying to convert >> + * it to NOP, kprobe should be notified and the kprobe data >> + * should be fixed at that time. >> + * >> + * Since it is possible that an early kprobe already on that >> + * place, don't return addr directly. >> + */ >> + if (likely(kprobes_on_ftrace_initialized)) >> + faddr = 0UL; >> + >> /* >> * Use the current code if it is not modified by Kprobe >> * and it cannot be modified by ftrace >> > > This is better, but I don't think we need bool XXX_initialized flags > for each subfunctions. Those should be serialized. > > Thank you, >
For this specific case, calling __recover_probed_insn() is mandatory for can_boost(). However, we can disallow early kprobes to be unregistered before ftrace is ready, and let ftrace fix all inconsistency by calling kprobe_on_ftrace_get_old_insn(). Which will make things simpler, and constrain the using scope of kprobes_on_ftrace_initialized to kernel/kprobes.c. The cost is unable to do smoke test for early ftrace because it will remove all kprobe before returning. I think it should be acceptable. What do you think? Thank you. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
