On Tue, Jun 23, 2020 at 05:38:55PM +0200, Joerg Roedel wrote:

On Tue, Jun 23, 2020 at 05:23:26PM +0200, Peter Zijlstra wrote:

quoted

Reliability of that depends on the unwinder, I wouldn't want the guess
uwinder to OOPS me by accident.

It doesn't use the full unwinder, it just assumes that there is a
pt_regs struct at the top of every kernel stack and walks through them
until SP points to a user-space stack.

As long as the assumption that there is a pt_regs struct on top of every
stack holds, this should be safe. The assumption might be wrong when an
exception happens during SYSCALL/SYSENTER entry, when the return frame
is not written by hardware.

The IRQ and SoftIRQ stacks don't have that I think. Only the task and
exception stacks.