> On Apr 28, 2019, at 2:22 PM, Nicolai Stange <nstange@xxxxxxx> wrote: > > Steven Rostedt <rostedt@xxxxxxxxxxx> writes: > >> On Sun, 28 Apr 2019 10:41:10 -0700 >> Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >> >> >>>> Note that at any given point >>>> in time, there can be at most four such call insn emulations pending: >>>> namely at most one per "process", "irq", "softirq" and "nmi" context. >>>> >>> >>> That’s quite an assumption. I think your list should also contain >>> exception, exceptions nested inside that exception, and machine >>> check, at the very least. I’m also wondering why irq and softirq are >>> treated separately. > > You're right, I missed the machine check case. > > >> 4 has usually been the context count we choose. But I guess in theory, >> if we get exceptions then I could potentially be more. > > After having seen the static_call discussion, I'm in no way defending > this limited approach here, but out of curiosity: can the code between > the push onto the stack from ftrace_int3_handler() and the subsequent > pop from the stub actually trigger an (non-#MC) exception? There's an > iret inbetween, but that can fault only when returning to user space, > correct? IRET doesn’t do any fancy masking, so #DB, NMI and regular IRQs should all be possible. > > >> As for irq vs softirq, an interrupt can preempt a softirq. Interrupts >> are enabled while softirqs are running. When sofirqs run, softirqs are >> disabled to prevent nested softirqs. But interrupts are enabled again, >> and another interrupt may come in while a softirq is executing. >> > > Thanks, > > Nicolai > > > -- > SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, > HRB 21284 (AG Nürnberg)
