On Fri, 28 Aug 2020 16:19:17 +0200 peterz@xxxxxxxxxxxxx wrote: > On Fri, Aug 28, 2020 at 02:11:18PM +0000, Eddy_Wu@xxxxxxxxxxxxxx wrote: > > > From: Masami Hiramatsu <mhiramat@xxxxxxxxxx> > > > > > > OK, schedule function will be the key. I guess the senario is.. > > > > > > 1) kretporbe replace the return address with kretprobe_trampoline on task1's kernel stack > > > 2) the task1 forks task2 before returning to the kretprobe_trampoline > > > 3) while copying the process with the kernel stack, task2->kretprobe_instances.first = NULL > > > > I think new process created by fork/clone uses a brand new kernel > > stack? I thought only user stack are copied. Otherwise any process > > launch should crash in the same way > > I was under the same impression, we create a brand new stack-frame for > the new task, this 'fake' frame we can schedule into. > > It either points to ret_from_fork() for new user tasks, or > kthread_frame_init() for kernel threads. Ah sorry, then it's my misreading... anyway, I could reproduce the crash with probing on schedule(). Hmm, it is better to dump the current comm with BUG(). Thank you, -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
