On Sat, 28 Oct 2017 09:26:56 +0800 zhouchengming <zhouchengmi...@huawei.com> wrote:
> On 2017/10/27 22:15, Peter Zijlstra wrote: > > On Fri, Oct 27, 2017 at 02:33:48PM +0200, Borislav Petkov wrote: > >> On Fri, Oct 27, 2017 at 07:42:45PM +0800, zhouchengming wrote: > >>> This is a real bug happened on one of our machines, below is the > >>> calltrace. > >>> We can see the trigger is at alternatives_text_reserved+0x20/0x80, and > >>> encounter a deleted (poisoned) list_head. > >> Looks like some out-of-tree, old kernel thing. We don't have > >> mlx4_stats_sysfs_create() upstream and looking at the boot timestamps, > >> it could be that register_jprobe() is not ready yet. > >> > >> Looking at the Code, though: > >> > >> 20: 74 59 je 0x7b > >> 22: 66 0f 1f 84 00 00 00 nopw 0x0(%rax,%rax,1) > >> 29: 00 00 > >> 2b:* 48 3b 71 20 cmp 0x20(%rcx),%rsi<-- trapping > >> instruction > >> 2f: 72 3a jb 0x6b > >> 31: 48 3b 79 28 cmp 0x28(%rcx),%rdi > >> 35: 77 34 ja 0x6b > >> > >> %rcx is 0xdead0000000000d0 and that is POISON_POINTER_DELTA + 0xd0 so > >> that looks more like smp_alt_modules is not initialized yet but I could > >> could very well be wrong because this is an old kernel. So trigger that > >> with the upstream kernel without out of tree modules. > > Not to mention that we're about (or just have) yanked jprobes out of the > > kernel entirely. > > Well... but this is a bug of alternatives_text_reserved(), it traverse the > list without holding > the smp_alt mutex. So all users of it, like kprobes, will still have this > problem. Maybe I could > think of a way to get rid of the mutex entirely. Correct. Peter, this is not related to jprobes, register_kprobe has same issue. Thank you, -- Masami Hiramatsu <mhira...@kernel.org>
