* Josh Poimboeuf <jpoim...@redhat.com> wrote:
> I haven't actually seen any real-world bugs caused by this, so I'm not
> sure how theoretical it is. I just stumbled upon it in code review when
> looking for another bug.
I believe it's a real bug, but the fix is wrong with irq tracing or lockdep
enabled as Dave points out.
I think the reason we haven't seen this bug yet is that "paranoid" entry points
are limited to:
idtentry double_fault do_double_fault
has_error_code=1 paranoid=2
idtentry debug do_debug has_error_code=0
paranoid=1 shift_ist=DEBUG_STACK
idtentry int3 do_int3 has_error_code=0
paranoid=1 shift_ist=DEBUG_STACK
idtentry machine_check do_mce has_error_code=0
paranoid=1
Only machine_check is one that will interrupt an IRQS-off critical section
asynchronously - and machine check events are rare.
The other main asynchronous entries are NMI entries, which can be very
high-freq
with perf profiling, but they are special: they don't use the 'idtentry' macro
but
are open coded and restore user CR3 unconditionally so don't seem to have this
bug.
Thanks,
Ingo
