[PATCH v2] mm,hwpoison: return -EBUSY when page already poisoned

[Aili Yao]

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 to mce looping, 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, The process B will re-excute instruction and get
into mce again and then loop happens. And also the set_mce_nospec()
here is not proper, may refer to commit fd0e786d9d09 ("x86/mm,
mm/hwpoison: Don't unconditionally unmap kernel 1:1 pages").

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.

Signed-off-by: Aili Yao <yaoaili@xxxxxxxxxxxx>
---
 mm/memory-failure.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 24210c9bd843..b6bc77460ee1 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1228,7 +1228,7 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
 	if (TestSetPageHWPoison(head)) {
 		pr_err("Memory failure: %#lx: already hardware poisoned\n",
 		       pfn);
-		return 0;
+		return -EBUSY;
 	}
 
 	num_poisoned_pages_inc();
@@ -1430,7 +1430,7 @@ int memory_failure(unsigned long pfn, int flags)
 	if (TestSetPageHWPoison(p)) {
 		pr_err("Memory failure: %#lx: already hardware poisoned\n",
 			pfn);
-		return 0;
+		return -EBUSY;
 	}
 
 	orig_head = hpage = compound_head(p);
-- 
2.25.1