Messages in this thread | | | Date | Sun, 11 Sep 2011 11:05:23 +0900 | From | Tejun Heo <> | Subject | Re: [PATCH v2] Make PTRACE_SEIZE set ptrace options specified in 'data' parameter |
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Hello,
On Thu, Sep 08, 2011 at 08:17:47PM +0200, Oleg Nesterov wrote: > > There are places which assume ->ptrace is protected by siglock. > > Really? Once again, I agree. But _afaics_ currently this is not strictly > needed. PT_PTRACED/PT_SEIZED should not go away under ->siglock, yes, but > it seems that it is fine to set them.
Hmmm.... I haven't checked each direction. Maybe we don't strictly need it on setting it but I definitely was assuming that ->ptrace was protected by siglock while coding recent ptrace changes. Can't the following happen?
* ptracer seizes child, sets PT_PTRACED and then OR PT_SEIZED.
* ptracee enters signal delivery path with group stop scheduled. PT_PTRACED is visible and group stop is transformed into JOBCTL_TRAP_STOP.
* ptracee enters do_jobct_trap(). PT_SEIZED is still not visible and it takes the path for the old behavior.
* ptracer SEIZE'd and expects PTRACE_EVENT_STOP but it gets the old no-siginfo trap.
> > and linking are protected by siglock > > Hmm. Could you explain this? Why do want __ptrace_link under ->siglock ?
Because it's much simpler to assume that w/ siglock locked, everything including ->parent is set up properly w.r.t. ->ptrace.
Thanks.
-- tejun
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