Re: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned

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On 24.02.21 08:16, Aili Yao wrote:
When the page is already poisoned, another memory_failure() call in the
same page now return 0, meaning OK. For nested memory mce handling, this
behavior may lead real serious problem, Example:

1.When LCME is enabled, and there are two processes A && B running on
different core X && Y separately, which will access one same page, then
the page corrupted when process A access it, a MCE will be rasied to
core X and the error process is just underway.

2.Then B access the page and trigger another MCE to core Y, it will also
do error process, it will see TestSetPageHWPoison be true, and 0 is
returned.

3.The kill_me_maybe will check the return:

1244 static void kill_me_maybe(struct callback_head *cb)
1245 {

1254         if (!memory_failure(p->mce_addr >> PAGE_SHIFT, flags) &&
1255             !(p->mce_kflags & MCE_IN_KERNEL_COPYIN)) {
1256                 set_mce_nospec(p->mce_addr >> PAGE_SHIFT,
p->mce_whole_page);
1257                 sync_core();
1258                 return;
1259         }

1267 }

4. The error process for B will end, and may nothing happened if
kill-early is not set, We may let the wrong data go into effect.

For other cases which care the return value of memory_failure() should
check why they want to process a memory error which have already been
processed. This behavior seems reasonable.

In kill_me_maybe, log the fact about the memory may not recovered, and
we will kill the related process.


Is -EBUSY then the right return value?

I'd expect if it's already poisoned that we would get something like EHWPOISON.

Does this affect existing user space interfaces (especially, via madvise?)?

--
Thanks,

David / dhildenb





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