Hi tony: > On Tue, 2 Mar 2021 19:39:53 -0800 > "Luck, Tony" <[email protected]> wrote: > > > On Fri, Feb 26, 2021 at 10:59:15AM +0800, Aili Yao wrote: > > > Hi naoya, tony: > > > > > > > > > > Idea for what we should do next ... Now that x86 is calling > > > > > memory_failure() > > > > > from user context ... maybe parallel calls for the same page should > > > > > be blocked until the first caller completes so we can: > > > > > a) know that pages are unmapped (if that happens) > > > > > b) all get the same success/fail status > > > > > > > > One memory_failure() call changes the target page's status and > > > > affects all mappings to all affected processes, so I think that > > > > (ideally) we don't have to block other threads (letting them > > > > early return seems fine). Sometimes memory_failure() fails, > > > > but even in such case, PG_hwpoison is set on the page and other > > > > threads properly get SIGBUSs with this patch, so I think that > > > > we can avoid the worst scenario (like system stall by MCE loop). > > > > > > > I agree with naoya's point, if we block for this issue, Does this change > > > the result > > > that the process should be killed? Or is there something other still need > > > to be considered? > > > > Ok ... no blocking ...
I do think about blocking method and the error address issue with sigbus,here is my opinion, maybe helpful: For blocking, if we block here, there are some undefine work i think should be done. As we don't know the process B triggering this error again is early-kill or not, so the previous memory_failure() call may not add B on kill_list, even if B is on kill_list, the error level for B is not proper set, as B should get an AR SIGBUS; So we can't just wait, We must have some logic adding the process B to kill list, and as this is an AR error another change should be done to current code, we need more logic in kill_proc or some other place. Even if all the work is done right. There is one more serious scenario though, we even don't know the current step the previous memory_failure() is on, So previous modification may not be usefull at all; When this scenario happens, what we can do? block or return ? if finally we return, an error code should be taken back; so we have to go to error process logic and a signal without right address will be sent; For error address with sigbus, i think this is not an issue resulted by the patch i post, before my patch, the issue is already there. I don't find a realizable way to get the correct address for same reason --- we don't know whether the page mapping is there or not when we got to kill_me_maybe(), in some case, we may get it, but there are a lot of parallel issue need to consider, and if failed we have to fallback to the error brach again, remaining current code may be an easy option; Any methods or patchs can solve the issue in a better way is OK to me, i want this issue fixed and in more complete way! -- Thanks! Aili Yao
