mm/memory-failure: use a mutex to avoid memory_failure() races

Patch series "mm,hwpoison: fix sending SIGBUS for Action Required MCE", v5.

I wrote this patchset to materialize what I think is the current
allowable solution mentioned by the previous discussion [1].  I simply
borrowed Tony's mutex patch and Aili's return code patch, then I queued
another one to find error virtual address in the best effort manner.  I
know that this is not a perfect solution, but should work for some
typical case.

[1]: https://lore.kernel.org/linux-mm/20210331192540.2141052f@alex-virtual-machine/

This patch (of 2):

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.

[[email protected]: make mf_mutex local to memory_failure()]

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Tony Luck <[email protected]>
Signed-off-by: Naoya Horiguchi <[email protected]>
Reviewed-by: Borislav Petkov <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: Aili Yao <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Jue Wang <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/memory-failure.c

@@ -1429,9 +1429,10 @@ 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;
+	static DEFINE_MUTEX(mf_mutex);
 
 	if (!sysctl_memory_failure_recovery)
 		panic("Memory failure on page %lx", pfn);
@@ -1449,13 +1450,18 @@ 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);
@@ -1488,17 +1494,19 @@ 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);
 	}
@@ -1522,7 +1530,7 @@ 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;
 	}
 
 	/*
@@ -1542,14 +1550,14 @@ 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;
 	}
 
 	/*
@@ -1573,7 +1581,7 @@ 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;
 	}
 
 	/*
@@ -1582,13 +1590,15 @@ 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);