Messages in this thread | | | Date | Tue, 28 Jan 2014 18:19:02 +0100 | From | Oleg Nesterov <> | Subject | Re: [RFC] de-asmify the x86-64 system call slowpath |
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On 01/28, Al Viro wrote: > > On Tue, Jan 28, 2014 at 05:38:08PM +0100, Oleg Nesterov wrote: > > On 01/28, Al Viro wrote: > > > > > > On Mon, Jan 27, 2014 at 06:39:31PM +0100, Oleg Nesterov wrote: > > > > On 01/27, Al Viro wrote: > > > > > > > > > > Why is _TIF_UPROBE *not* a part > > > > > of _TIF_DO_NOTIFY_MASK, for example? > > > > > > > > Yes, please see another email. That is why uprobe_deny_signal() > > > > sets TIF_NOTIFY_RESUME along with TIF_UPROBE. > > > > > > *grumble* Can it end up modifying *regs? From very cursory reading of > > > kernel/events/uprobe.c it seems to do so, so we probably want to leave > > > via iretq if that has hit, right? > > > > But we do this anyway, restore_args path does iretq? > > > > I mean, uprobe_notify_resume() is called from do_notify_resume(), it > > should be fine to modify*regs there? > > See Linus' patch trying to avoid iretq path; it's really costly. Looks > like that patch will have to treat _TIF_UPROBE the same way it treats > _TIF_SIGPENDING...
Ah, this one I guess: http://marc.info/?l=linux-kernel&m=139077532507926
I think this should be fine wrt uprobes, unless I misread this patch syscall_exit_slowpath() is actually only called by ret_from_sys_call path, it this case TIF_UPROBE should not be set. But perhaps "retval = 1" after uprobe_notify_resume() makes sense anyway.
And while I am almost sure I missed something, can't we (with or without that patch) simply add TIF_UPROBE into _TIF_DO_NOTIFY_MASK and remove set_tsk_thread_flag(t, TIF_NOTIFY_RESUME) from uprobe_deny_signal ?
Oleg.
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