On Tue, Jul 29, 2014 at 9:54 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > On 07/28, Andy Lutomirski wrote: >> >> On Mon, Jul 28, 2014 at 10:37 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: >> > Hi Andy, >> > >> > I am really sorry for delay. >> > >> > This is on top of the recent change from Kees, right? Could me remind me >> > where can I found the tree this series based on? So that I could actually >> > apply these changes... >> >> https://git.kernel.org/cgit/linux/kernel/git/kees/linux.git/log/?h=seccomp/fastpath >> >> The first four patches are already applied there. > > Thanks! > >> > If I understand correctly, syscall_trace_enter() can avoid _phase2() above. >> > But we should always call user_exit() unconditionally? >> >> Damnit. I read that every function called by user_exit, and none of >> them give any indication of why they're needed for traced syscalls but >> not for untraced syscalls. On a second look, it seems that TIF_NOHZ >> controls it. > > Yes, just to trigger the slow path, I guess. > >> I'll update the code to call user_exit iff TIF_NOHZ is >> set. > > Or perhaps it would be better to not add another user of this (strange) flag > and just call user_exit() unconditionally(). But, yes, you need to use > from "work = flags & (_TIF_WORK_SYSCALL_ENTRY & ~TIF_NOHZ)" then.\ user_exit looks slow enough to me that a branch to try to avoid it may be worthwhile. I bet that explicitly checking the flag is actually both faster and clearer. That's what I did for v4. --Andy > >> > And we should always set X86_EFLAGS_TF if TIF_SINGLESTEP? IIRC, TF can be >> > actually cleared on a 32bit kernel if we step over sysenter insn? >> >> I don't follow. If TIF_SINGLESTEP, then phase1 will return a nonzero >> value, > > Ah yes, thanks, I missed this. > > Oleg. > -- Andy Lutomirski AMA Capital Management, LLC
