On 11/12/16 04:17, Josh Poimboeuf wrote: > On Sat, Dec 10, 2016 at 04:46:17PM +1100, Balbir Singh wrote: >> On Thu, 2016-12-08 at 12:08 -0600, Josh Poimboeuf wrote: >>> Dusting the cobwebs off the consistency model again. This is based on >>> linux-next/master. >>> >>> v1 was posted on 2015-02-09: >>> >>> https://lkml.kernel.org/r/cover.1423499826.git.jpoimboe@xxxxxxxxxx >>> >>> v2 was posted on 2016-04-28: >>> >>> https://lkml.kernel.org/r/cover.1461875890.git.jpoimboe@xxxxxxxxxx >>> >>> The biggest issue from v2 was finding a decent way to detect preemption >>> and page faults on the stack of a sleeping task. >> >> Could you please elaborate on this? Preemption of a sleeping task and >> faults as in the future (time) preemption and faults? > > The normal way for a task to go to sleep is to call schedule(). objtool > ensures the stack trace is reliable in that case, by making sure that > all functions save the frame pointer on the stack before calling out to > another function. > > But a task can also go to sleep in a few other ways. One way is by > preemption, where an interrupt handler interrupts the task and calls > preempt_schedule_irq(). It's preempted, not sleeping. It's on_rq but not on_cpu. Another way is by a page fault exception. In > both cases, there's no guarantee that the interrupted function saved the > frame pointer on the stack beforehand. So the stack trace might be > unreliable. Fortunately, interrupts and exceptions leave evidence > behind on the stack. So when walking the stack of a sleeping task, we > can detect when an IRQ or exception occurred, and consider such a stack > unreliable. > Thanks for the explanation. I presume a whole lot of this is arch specific code? I'll look at the patches as well Balbir -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
