On Fri, Sep 19, 2025 at 04:34:02PM -0700, Josh Poimboeuf wrote: > On Thu, Sep 18, 2025 at 03:10:18PM -0400, Steven Rostedt wrote: > > On Thu, 18 Sep 2025 19:32:20 +0200 > > Peter Zijlstra <[email protected]> wrote: > > > > > > Now, task_work_run() is in the exit_to_user_mode_loop() which is notably > > > > *before* exit_to_user_mode() which does the unwind_reset_info(). > > > > > > > > What happens if we get an NMI requesting an unwind after > > > > unwind_reset_info() while still very much being in the kernel on the way > > > > out? > > > > > > AFAICT it will try and do a task_work_add(TWA_RESUME) from NMI context, > > > and this will fail horribly. > > > > > > If you do something like: > > > > > > twa_mode = in_nmi() ? TWA_NMI_CURRENT : TWA_RESUME; > > > task_work_add(foo, twa_mode); > > > > > > it might actually work. > > > > Ah, the comment for TWA_RESUME didn't express this restriction. > > > > That does look like that would work as the way I expected task_work to > > handle this case. > > BTW, I remember Peter had a fix for TWA_NMI_CURRENT, I guess it got lost > in the shuffle or did something else happen in the meantime? > > > https://lore.kernel.org/[email protected]
Oh, yeah, I had completely forgotten about all that :-) I'll go stick it in the pile. Thanks!
