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Subject[PATCH v4 1/2] mm/memory-failure: Use a mutex to avoid memory_failure() races
Date
From: Tony Luck <tony.luck@intel.com>

There can be races when multiple CPUs consume poison from the same
page. The first into memory_failure() atomically sets the HWPoison
page flag and begins hunting for tasks that map this page. Eventually
it invalidates those mappings and may send a SIGBUS to the affected
tasks.

But while all that work is going on, other CPUs see a "success"
return code from memory_failure() and so they believe the error
has been handled and continue executing.

Fix by wrapping most of the internal parts of memory_failure() in
a mutex.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
---
mm/memory-failure.c | 37 ++++++++++++++++++++++++-------------
1 file changed, 24 insertions(+), 13 deletions(-)

diff --git v5.12/mm/memory-failure.c v5.12_patched/mm/memory-failure.c
index 24210c9bd843..4087308e4b32 100644
--- v5.12/mm/memory-failure.c
+++ v5.12_patched/mm/memory-failure.c
@@ -1381,6 +1381,8 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
return rc;
}

+static DEFINE_MUTEX(mf_mutex);
+
/**
* memory_failure - Handle memory failure of a page.
* @pfn: Page Number of the corrupted page
@@ -1404,7 +1406,7 @@ int memory_failure(unsigned long pfn, int flags)
struct page *hpage;
struct page *orig_head;
struct dev_pagemap *pgmap;
- int res;
+ int res = 0;
unsigned long page_flags;
bool retry = true;

@@ -1424,13 +1426,18 @@ int memory_failure(unsigned long pfn, int flags)
return -ENXIO;
}

+ mutex_lock(&mf_mutex);
+
try_again:
- if (PageHuge(p))
- return memory_failure_hugetlb(pfn, flags);
+ if (PageHuge(p)) {
+ res = memory_failure_hugetlb(pfn, flags);
+ goto unlock_mutex;
+ }
+
if (TestSetPageHWPoison(p)) {
pr_err("Memory failure: %#lx: already hardware poisoned\n",
pfn);
- return 0;
+ goto unlock_mutex;
}

orig_head = hpage = compound_head(p);
@@ -1463,17 +1470,19 @@ int memory_failure(unsigned long pfn, int flags)
res = MF_FAILED;
}
action_result(pfn, MF_MSG_BUDDY, res);
- return res == MF_RECOVERED ? 0 : -EBUSY;
+ res = res == MF_RECOVERED ? 0 : -EBUSY;
} else {
action_result(pfn, MF_MSG_KERNEL_HIGH_ORDER, MF_IGNORED);
- return -EBUSY;
+ res = -EBUSY;
}
+ goto unlock_mutex;
}

if (PageTransHuge(hpage)) {
if (try_to_split_thp_page(p, "Memory Failure") < 0) {
action_result(pfn, MF_MSG_UNSPLIT_THP, MF_IGNORED);
- return -EBUSY;
+ res = -EBUSY;
+ goto unlock_mutex;
}
VM_BUG_ON_PAGE(!page_count(p), p);
}
@@ -1497,7 +1506,7 @@ int memory_failure(unsigned long pfn, int flags)
if (PageCompound(p) && compound_head(p) != orig_head) {
action_result(pfn, MF_MSG_DIFFERENT_COMPOUND, MF_IGNORED);
res = -EBUSY;
- goto out;
+ goto unlock_page;
}

/*
@@ -1517,14 +1526,14 @@ int memory_failure(unsigned long pfn, int flags)
num_poisoned_pages_dec();
unlock_page(p);
put_page(p);
- return 0;
+ goto unlock_mutex;
}
if (hwpoison_filter(p)) {
if (TestClearPageHWPoison(p))
num_poisoned_pages_dec();
unlock_page(p);
put_page(p);
- return 0;
+ goto unlock_mutex;
}

if (!PageTransTail(p) && !PageLRU(p))
@@ -1543,7 +1552,7 @@ int memory_failure(unsigned long pfn, int flags)
if (!hwpoison_user_mappings(p, pfn, flags, &p)) {
action_result(pfn, MF_MSG_UNMAP_FAILED, MF_IGNORED);
res = -EBUSY;
- goto out;
+ goto unlock_page;
}

/*
@@ -1552,13 +1561,15 @@ int memory_failure(unsigned long pfn, int flags)
if (PageLRU(p) && !PageSwapCache(p) && p->mapping == NULL) {
action_result(pfn, MF_MSG_TRUNCATED_LRU, MF_IGNORED);
res = -EBUSY;
- goto out;
+ goto unlock_page;
}

identify_page_state:
res = identify_page_state(pfn, p, page_flags);
-out:
+unlock_page:
unlock_page(p);
+unlock_mutex:
+ mutex_unlock(&mf_mutex);
return res;
}
EXPORT_SYMBOL_GPL(memory_failure);
--
2.25.1
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