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

[Aili Yao <yaoaili@kingsoft.com>]

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.

Signed-off-by: Aili Yao <yaoaili@kingsoft.com>
---
 arch/x86/kernel/cpu/mce/core.c | 2 ++
 mm/memory-failure.c            | 4 ++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index e133ce1e562b..db4afc5bf15a 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1259,6 +1259,8 @@ static void kill_me_maybe(struct callback_head *cb)
 	}
 
 	if (p->mce_vaddr != (void __user *)-1l) {
+		pr_err("Memory error may not recovered: %#lx: Sending SIGBUS to %s:%d due to hardware memory corruption\n",
+			p->mce_addr >> PAGE_SHIFT, p->comm, p->pid);
 		force_sig_mceerr(BUS_MCEERR_AR, p->mce_vaddr, PAGE_SHIFT);
 	} else {
 		pr_err("Memory error not recovered");
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index e9481632fcd1..06f006174b8c 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1224,7 +1224,7 @@ 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();
@@ -1420,7 +1420,7 @@ 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