[5.4 PATCH 0/4] Fix a CONFIG_READ_ONLY_THP_FOR_FS bug

[5.4 PATCH 0/4] Fix a CONFIG_READ_ONLY_THP_FOR_FS bug

[Matthew Wilcox (Oracle)]

This experimental feature has had a few bugs, but it has enough of
a performance effect that customers are actually asking for it to be
enabled.  So we should apply this upstream bugfix that needs a little
massaging to backport.  The first three patches enable the fix in the
fourth patch.  I've run the XArray test-suite after applying these
patches, and it continues to pass.

Matthew Wilcox (Oracle) (4):
  mm: add thp_order
  XArray: add xa_get_order
  XArray: add xas_split
  mm/filemap: fix storing to a THP shadow entry

 Documentation/core-api/xarray.rst |  16 ++-
 include/linux/huge_mm.h           |  19 +++
 include/linux/xarray.h            |  22 ++++
 lib/test_xarray.c                 |  65 ++++++++++
 lib/xarray.c                      | 208 ++++++++++++++++++++++++++++--
 mm/filemap.c                      |  37 ++++--
 6 files changed, 342 insertions(+), 25 deletions(-)

-- 
2.30.2

[PATCH 1/4] mm: add thp_order

[Matthew Wilcox (Oracle)]

commit 6ffbb45826f5d9ae09aa60cd88594b7816c96190 upstream

This function returns the order of a transparent huge page.  It compiles
to 0 if CONFIG_TRANSPARENT_HUGEPAGE is disabled.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Link: http://lkml.kernel.org/r/20200629151959.15779-4-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 include/linux/huge_mm.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 93d5cf0bc716..d8b86fd39113 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -231,6 +231,19 @@ static inline spinlock_t *pud_trans_huge_lock(pud_t *pud,
 	else
 		return NULL;
 }
+
+/**
+ * thp_order - Order of a transparent huge page.
+ * @page: Head page of a transparent huge page.
+ */
+static inline unsigned int thp_order(struct page *page)
+{
+	VM_BUG_ON_PGFLAGS(PageTail(page), page);
+	if (PageHead(page))
+		return HPAGE_PMD_ORDER;
+	return 0;
+}
+
 static inline int hpage_nr_pages(struct page *page)
 {
 	if (unlikely(PageTransHuge(page)))
@@ -290,6 +303,12 @@ static inline struct list_head *page_deferred_list(struct page *page)
 #define HPAGE_PUD_MASK ({ BUILD_BUG(); 0; })
 #define HPAGE_PUD_SIZE ({ BUILD_BUG(); 0; })
 
+static inline unsigned int thp_order(struct page *page)
+{
+	VM_BUG_ON_PGFLAGS(PageTail(page), page);
+	return 0;
+}
+
 #define hpage_nr_pages(x) 1
 
 static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
-- 
2.30.2

[PATCH 2/4] XArray: add xa_get_order

[Matthew Wilcox (Oracle)]

commit 57417cebc96b57122a2207fc84a6077d20c84b4b upstream

Patch series "Fix read-only THP for non-tmpfs filesystems".

As described more verbosely in the [3/3] changelog, we can inadvertently
put an order-0 page in the page cache which occupies 512 consecutive
entries.  Users are running into this if they enable the
READ_ONLY_THP_FOR_FS config option; see
https://bugzilla.kernel.org/show_bug.cgi?id=206569 and Qian Cai has also
reported it here:
https://lore.kernel.org/lkml/20200616013309.GB815@lca.pw/

This is a rather intrusive way of fixing the problem, but has the
advantage that I've actually been testing it with the THP patches, which
means that it sees far more use than it does upstream -- indeed, Song has
been entirely unable to reproduce it.  It also has the advantage that it
removes a few patches from my gargantuan backlog of THP patches.

This patch (of 3):

This function returns the order of the entry at the index.  We need this
because there isn't space in the shadow entry to encode its order.

[akpm@linux-foundation.org: export xa_get_order to modules]

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Qian Cai <cai@lca.pw>
Cc: Song Liu <songliubraving@fb.com>
Link: https://lkml.kernel.org/r/20200903183029.14930-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20200903183029.14930-2-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 include/linux/xarray.h |  9 +++++++++
 lib/test_xarray.c      | 21 +++++++++++++++++++++
 lib/xarray.c           | 40 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 70 insertions(+)

diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 3b257c97837d..63185fe7cd6a 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -1470,6 +1470,15 @@ void xas_pause(struct xa_state *);
 
 void xas_create_range(struct xa_state *);
 
+#ifdef CONFIG_XARRAY_MULTI
+int xa_get_order(struct xarray *, unsigned long index);
+#else
+static inline int xa_get_order(struct xarray *xa, unsigned long index)
+{
+	return 0;
+}
+#endif
+
 /**
  * xas_reload() - Refetch an entry from the xarray.
  * @xas: XArray operation state.
diff --git a/lib/test_xarray.c b/lib/test_xarray.c
index d4f97925dbd8..bdd4d7995f79 100644
--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -1649,6 +1649,26 @@ static noinline void check_account(struct xarray *xa)
 #endif
 }
 
+static noinline void check_get_order(struct xarray *xa)
+{
+	unsigned int max_order = IS_ENABLED(CONFIG_XARRAY_MULTI) ? 20 : 1;
+	unsigned int order;
+	unsigned long i, j;
+
+	for (i = 0; i < 3; i++)
+		XA_BUG_ON(xa, xa_get_order(xa, i) != 0);
+
+	for (order = 0; order < max_order; order++) {
+		for (i = 0; i < 10; i++) {
+			xa_store_order(xa, i << order, order,
+					xa_mk_index(i << order), GFP_KERNEL);
+			for (j = i << order; j < (i + 1) << order; j++)
+				XA_BUG_ON(xa, xa_get_order(xa, j) != order);
+			xa_erase(xa, i << order);
+		}
+	}
+}
+
 static noinline void check_destroy(struct xarray *xa)
 {
 	unsigned long index;
@@ -1697,6 +1717,7 @@ static int xarray_checks(void)
 	check_reserve(&array);
 	check_reserve(&xa0);
 	check_multi_store(&array);
+	check_get_order(&array);
 	check_xa_alloc();
 	check_find(&array);
 	check_find_entry(&array);
diff --git a/lib/xarray.c b/lib/xarray.c
index 08d71c7b7599..57b9c144f793 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1592,6 +1592,46 @@ void *xa_store_range(struct xarray *xa, unsigned long first,
 	return xas_result(&xas, NULL);
 }
 EXPORT_SYMBOL(xa_store_range);
+
+/**
+ * xa_get_order() - Get the order of an entry.
+ * @xa: XArray.
+ * @index: Index of the entry.
+ *
+ * Return: A number between 0 and 63 indicating the order of the entry.
+ */
+int xa_get_order(struct xarray *xa, unsigned long index)
+{
+	XA_STATE(xas, xa, index);
+	void *entry;
+	int order = 0;
+
+	rcu_read_lock();
+	entry = xas_load(&xas);
+
+	if (!entry)
+		goto unlock;
+
+	if (!xas.xa_node)
+		goto unlock;
+
+	for (;;) {
+		unsigned int slot = xas.xa_offset + (1 << order);
+
+		if (slot >= XA_CHUNK_SIZE)
+			break;
+		if (!xa_is_sibling(xas.xa_node->slots[slot]))
+			break;
+		order++;
+	}
+
+	order += xas.xa_node->shift;
+unlock:
+	rcu_read_unlock();
+
+	return order;
+}
+EXPORT_SYMBOL(xa_get_order);
 #endif /* CONFIG_XARRAY_MULTI */
 
 /**
-- 
2.30.2

[PATCH 3/4] XArray: add xas_split

[Matthew Wilcox (Oracle)]

commit 8fc75643c5e14574c8be59b69182452ece28315a upstream

In order to use multi-index entries for huge pages in the page cache, we
need to be able to split a multi-index entry (eg if a file is truncated in
the middle of a huge page entry).  This version does not support splitting
more than one level of the tree at a time.  This is an acceptable
limitation for the page cache as we do not expect to support order-12
pages in the near future.

[akpm@linux-foundation.org: export xas_split_alloc() to modules]
[willy@infradead.org: fix xarray split]
  Link: https://lkml.kernel.org/r/20200910175450.GV6583@casper.infradead.org
[willy@infradead.org: fix xarray]
  Link: https://lkml.kernel.org/r/20201001233943.GW20115@casper.infradead.org

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Qian Cai <cai@lca.pw>
Cc: Song Liu <songliubraving@fb.com>
Link: https://lkml.kernel.org/r/20200903183029.14930-3-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 Documentation/core-api/xarray.rst |  16 +--
 include/linux/xarray.h            |  13 +++
 lib/test_xarray.c                 |  44 ++++++++
 lib/xarray.c                      | 168 ++++++++++++++++++++++++++++--
 4 files changed, 225 insertions(+), 16 deletions(-)

diff --git a/Documentation/core-api/xarray.rst b/Documentation/core-api/xarray.rst
index fcedc5349ace..2ad3c1fce579 100644
--- a/Documentation/core-api/xarray.rst
+++ b/Documentation/core-api/xarray.rst
@@ -461,13 +461,15 @@ or iterations will move the index to the first index in the range.
 Each entry will only be returned once, no matter how many indices it
 occupies.
 
-Using xas_next() or xas_prev() with a multi-index xa_state
-is not supported.  Using either of these functions on a multi-index entry
-will reveal sibling entries; these should be skipped over by the caller.
-
-Storing ``NULL`` into any index of a multi-index entry will set the entry
-at every index to ``NULL`` and dissolve the tie.  Splitting a multi-index
-entry into entries occupying smaller ranges is not yet supported.
+Using xas_next() or xas_prev() with a multi-index xa_state is not
+supported.  Using either of these functions on a multi-index entry will
+reveal sibling entries; these should be skipped over by the caller.
+
+Storing ``NULL`` into any index of a multi-index entry will set the
+entry at every index to ``NULL`` and dissolve the tie.  A multi-index
+entry can be split into entries occupying smaller ranges by calling
+xas_split_alloc() without the xa_lock held, followed by taking the lock
+and calling xas_split().
 
 Functions and structures
 ========================
diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 63185fe7cd6a..2903f25bff5e 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -1472,11 +1472,24 @@ void xas_create_range(struct xa_state *);
 
 #ifdef CONFIG_XARRAY_MULTI
 int xa_get_order(struct xarray *, unsigned long index);
+void xas_split(struct xa_state *, void *entry, unsigned int order);
+void xas_split_alloc(struct xa_state *, void *entry, unsigned int order, gfp_t);
 #else
 static inline int xa_get_order(struct xarray *xa, unsigned long index)
 {
 	return 0;
 }
+
+static inline void xas_split(struct xa_state *xas, void *entry,
+		unsigned int order)
+{
+	xas_store(xas, entry);
+}
+
+static inline void xas_split_alloc(struct xa_state *xas, void *entry,
+		unsigned int order, gfp_t gfp)
+{
+}
 #endif
 
 /**
diff --git a/lib/test_xarray.c b/lib/test_xarray.c
index bdd4d7995f79..8262c3f05a5d 100644
--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -1503,6 +1503,49 @@ static noinline void check_store_range(struct xarray *xa)
 	}
 }
 
+#ifdef CONFIG_XARRAY_MULTI
+static void check_split_1(struct xarray *xa, unsigned long index,
+							unsigned int order)
+{
+	XA_STATE(xas, xa, index);
+	void *entry;
+	unsigned int i = 0;
+
+	xa_store_order(xa, index, order, xa, GFP_KERNEL);
+
+	xas_split_alloc(&xas, xa, order, GFP_KERNEL);
+	xas_lock(&xas);
+	xas_split(&xas, xa, order);
+	xas_unlock(&xas);
+
+	xa_for_each(xa, index, entry) {
+		XA_BUG_ON(xa, entry != xa);
+		i++;
+	}
+	XA_BUG_ON(xa, i != 1 << order);
+
+	xa_set_mark(xa, index, XA_MARK_0);
+	XA_BUG_ON(xa, !xa_get_mark(xa, index, XA_MARK_0));
+
+	xa_destroy(xa);
+}
+
+static noinline void check_split(struct xarray *xa)
+{
+	unsigned int order;
+
+	XA_BUG_ON(xa, !xa_empty(xa));
+
+	for (order = 1; order < 2 * XA_CHUNK_SHIFT; order++) {
+		check_split_1(xa, 0, order);
+		check_split_1(xa, 1UL << order, order);
+		check_split_1(xa, 3UL << order, order);
+	}
+}
+#else
+static void check_split(struct xarray *xa) { }
+#endif
+
 static void check_align_1(struct xarray *xa, char *name)
 {
 	int i;
@@ -1729,6 +1772,7 @@ static int xarray_checks(void)
 	check_store_range(&array);
 	check_store_iter(&array);
 	check_align(&xa0);
+	check_split(&array);
 
 	check_workingset(&array, 0);
 	check_workingset(&array, 64);
diff --git a/lib/xarray.c b/lib/xarray.c
index 57b9c144f793..7d22b3059127 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -266,13 +266,14 @@ static void xa_node_free(struct xa_node *node)
  */
 static void xas_destroy(struct xa_state *xas)
 {
-	struct xa_node *node = xas->xa_alloc;
+	struct xa_node *next, *node = xas->xa_alloc;
 
-	if (!node)
-		return;
-	XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
-	kmem_cache_free(radix_tree_node_cachep, node);
-	xas->xa_alloc = NULL;
+	while (node) {
+		XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
+		next = rcu_dereference_raw(node->parent);
+		radix_tree_node_rcu_free(&node->rcu_head);
+		xas->xa_alloc = node = next;
+	}
 }
 
 /**
@@ -304,6 +305,7 @@ bool xas_nomem(struct xa_state *xas, gfp_t gfp)
 	xas->xa_alloc = kmem_cache_alloc(radix_tree_node_cachep, gfp);
 	if (!xas->xa_alloc)
 		return false;
+	xas->xa_alloc->parent = NULL;
 	XA_NODE_BUG_ON(xas->xa_alloc, !list_empty(&xas->xa_alloc->private_list));
 	xas->xa_node = XAS_RESTART;
 	return true;
@@ -339,6 +341,7 @@ static bool __xas_nomem(struct xa_state *xas, gfp_t gfp)
 	}
 	if (!xas->xa_alloc)
 		return false;
+	xas->xa_alloc->parent = NULL;
 	XA_NODE_BUG_ON(xas->xa_alloc, !list_empty(&xas->xa_alloc->private_list));
 	xas->xa_node = XAS_RESTART;
 	return true;
@@ -403,7 +406,7 @@ static unsigned long xas_size(const struct xa_state *xas)
 /*
  * Use this to calculate the maximum index that will need to be created
  * in order to add the entry described by @xas.  Because we cannot store a
- * multiple-index entry at index 0, the calculation is a little more complex
+ * multi-index entry at index 0, the calculation is a little more complex
  * than you might expect.
  */
 static unsigned long xas_max(struct xa_state *xas)
@@ -946,6 +949,153 @@ void xas_init_marks(const struct xa_state *xas)
 }
 EXPORT_SYMBOL_GPL(xas_init_marks);
 
+#ifdef CONFIG_XARRAY_MULTI
+static unsigned int node_get_marks(struct xa_node *node, unsigned int offset)
+{
+	unsigned int marks = 0;
+	xa_mark_t mark = XA_MARK_0;
+
+	for (;;) {
+		if (node_get_mark(node, offset, mark))
+			marks |= 1 << (__force unsigned int)mark;
+		if (mark == XA_MARK_MAX)
+			break;
+		mark_inc(mark);
+	}
+
+	return marks;
+}
+
+static void node_set_marks(struct xa_node *node, unsigned int offset,
+			struct xa_node *child, unsigned int marks)
+{
+	xa_mark_t mark = XA_MARK_0;
+
+	for (;;) {
+		if (marks & (1 << (__force unsigned int)mark)) {
+			node_set_mark(node, offset, mark);
+			if (child)
+				node_mark_all(child, mark);
+		}
+		if (mark == XA_MARK_MAX)
+			break;
+		mark_inc(mark);
+	}
+}
+
+/**
+ * xas_split_alloc() - Allocate memory for splitting an entry.
+ * @xas: XArray operation state.
+ * @entry: New entry which will be stored in the array.
+ * @order: New entry order.
+ * @gfp: Memory allocation flags.
+ *
+ * This function should be called before calling xas_split().
+ * If necessary, it will allocate new nodes (and fill them with @entry)
+ * to prepare for the upcoming split of an entry of @order size into
+ * entries of the order stored in the @xas.
+ *
+ * Context: May sleep if @gfp flags permit.
+ */
+void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order,
+		gfp_t gfp)
+{
+	unsigned int sibs = (1 << (order % XA_CHUNK_SHIFT)) - 1;
+	unsigned int mask = xas->xa_sibs;
+
+	/* XXX: no support for splitting really large entries yet */
+	if (WARN_ON(xas->xa_shift + 2 * XA_CHUNK_SHIFT < order))
+		goto nomem;
+	if (xas->xa_shift + XA_CHUNK_SHIFT > order)
+		return;
+
+	do {
+		unsigned int i;
+		void *sibling;
+		struct xa_node *node;
+
+		node = kmem_cache_alloc(radix_tree_node_cachep, gfp);
+		if (!node)
+			goto nomem;
+		node->array = xas->xa;
+		for (i = 0; i < XA_CHUNK_SIZE; i++) {
+			if ((i & mask) == 0) {
+				RCU_INIT_POINTER(node->slots[i], entry);
+				sibling = xa_mk_sibling(0);
+			} else {
+				RCU_INIT_POINTER(node->slots[i], sibling);
+			}
+		}
+		RCU_INIT_POINTER(node->parent, xas->xa_alloc);
+		xas->xa_alloc = node;
+	} while (sibs-- > 0);
+
+	return;
+nomem:
+	xas_destroy(xas);
+	xas_set_err(xas, -ENOMEM);
+}
+EXPORT_SYMBOL_GPL(xas_split_alloc);
+
+/**
+ * xas_split() - Split a multi-index entry into smaller entries.
+ * @xas: XArray operation state.
+ * @entry: New entry to store in the array.
+ * @order: New entry order.
+ *
+ * The value in the entry is copied to all the replacement entries.
+ *
+ * Context: Any context.  The caller should hold the xa_lock.
+ */
+void xas_split(struct xa_state *xas, void *entry, unsigned int order)
+{
+	unsigned int sibs = (1 << (order % XA_CHUNK_SHIFT)) - 1;
+	unsigned int offset, marks;
+	struct xa_node *node;
+	void *curr = xas_load(xas);
+	int values = 0;
+
+	node = xas->xa_node;
+	if (xas_top(node))
+		return;
+
+	marks = node_get_marks(node, xas->xa_offset);
+
+	offset = xas->xa_offset + sibs;
+	do {
+		if (xas->xa_shift < node->shift) {
+			struct xa_node *child = xas->xa_alloc;
+
+			xas->xa_alloc = rcu_dereference_raw(child->parent);
+			child->shift = node->shift - XA_CHUNK_SHIFT;
+			child->offset = offset;
+			child->count = XA_CHUNK_SIZE;
+			child->nr_values = xa_is_value(entry) ?
+					XA_CHUNK_SIZE : 0;
+			RCU_INIT_POINTER(child->parent, node);
+			node_set_marks(node, offset, child, marks);
+			rcu_assign_pointer(node->slots[offset],
+					xa_mk_node(child));
+			if (xa_is_value(curr))
+				values--;
+		} else {
+			unsigned int canon = offset - xas->xa_sibs;
+
+			node_set_marks(node, canon, NULL, marks);
+			rcu_assign_pointer(node->slots[canon], entry);
+			while (offset > canon)
+				rcu_assign_pointer(node->slots[offset--],
+						xa_mk_sibling(canon));
+			values += (xa_is_value(entry) - xa_is_value(curr)) *
+					(xas->xa_sibs + 1);
+		}
+	} while (offset-- > xas->xa_offset);
+
+	node->nr_values += values;
+}
+EXPORT_SYMBOL_GPL(xas_split);
+#endif
+
 /**
  * xas_pause() - Pause a walk to drop a lock.
  * @xas: XArray operation state.
@@ -1407,7 +1557,7 @@ EXPORT_SYMBOL(__xa_store);
  * @gfp: Memory allocation flags.
  *
  * After this function returns, loads from this index will return @entry.
- * Storing into an existing multislot entry updates the entry of every index.
+ * Storing into an existing multi-index entry updates the entry of every index.
  * The marks associated with @index are unaffected unless @entry is %NULL.
  *
  * Context: Any context.  Takes and releases the xa_lock.
@@ -1549,7 +1699,7 @@ static void xas_set_range(struct xa_state *xas, unsigned long first,
  *
  * After this function returns, loads from any index between @first and @last,
  * inclusive will return @entry.
- * Storing into an existing multislot entry updates the entry of every index.
+ * Storing into an existing multi-index entry updates the entry of every index.
  * The marks associated with @index are unaffected unless @entry is %NULL.
  *
  * Context: Process context.  Takes and releases the xa_lock.  May sleep
-- 
2.30.2

[PATCH 4/4] mm/filemap: fix storing to a THP shadow entry

[Matthew Wilcox (Oracle)]

commit 198b62f83eef1d605d70eca32759c92cdcc14175 upstream

When a THP is removed from the page cache by reclaim, we replace it with a
shadow entry that occupies all slots of the XArray previously occupied by
the THP.  If the user then accesses that page again, we only allocate a
single page, but storing it into the shadow entry replaces all entries
with that one page.  That leads to bugs like

page dumped because: VM_BUG_ON_PAGE(page_to_pgoff(page) != offset)
------------[ cut here ]------------
kernel BUG at mm/filemap.c:2529!

https://bugzilla.kernel.org/show_bug.cgi?id=206569

This is hard to reproduce with mainline, but happens regularly with the
THP patchset (as so many more THPs are created).  This solution is take
from the THP patchset.  It splits the shadow entry into order-0 pieces at
the time that we bring a new page into cache.

Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Qian Cai <cai@lca.pw>
Link: https://lkml.kernel.org/r/20200903183029.14930-4-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 mm/filemap.c | 37 ++++++++++++++++++++++++++++---------
 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index db542b494883..c10e237cc2c6 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -856,7 +856,6 @@ noinline int __add_to_page_cache_locked(struct page *page,
 	int huge = PageHuge(page);
 	struct mem_cgroup *memcg;
 	int error;
-	void *old;
 
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 	VM_BUG_ON_PAGE(PageSwapBacked(page), page);
@@ -872,21 +871,41 @@ noinline int __add_to_page_cache_locked(struct page *page,
 	get_page(page);
 	page->mapping = mapping;
 	page->index = offset;
+	gfp_mask &= GFP_RECLAIM_MASK;
 
 	do {
+		unsigned int order = xa_get_order(xas.xa, xas.xa_index);
+		void *entry, *old = NULL;
+
+		if (order > thp_order(page))
+			xas_split_alloc(&xas, xa_load(xas.xa, xas.xa_index),
+					order, gfp_mask);
 		xas_lock_irq(&xas);
-		old = xas_load(&xas);
-		if (old && !xa_is_value(old))
-			xas_set_err(&xas, -EEXIST);
+		xas_for_each_conflict(&xas, entry) {
+			old = entry;
+			if (!xa_is_value(entry)) {
+				xas_set_err(&xas, -EEXIST);
+				goto unlock;
+			}
+		}
+
+		if (old) {
+			if (shadowp)
+				*shadowp = old;
+			/* entry may have been split before we acquired lock */
+			order = xa_get_order(xas.xa, xas.xa_index);
+			if (order > thp_order(page)) {
+				xas_split(&xas, old, order);
+				xas_reset(&xas);
+			}
+		}
+
 		xas_store(&xas, page);
 		if (xas_error(&xas))
 			goto unlock;
 
-		if (xa_is_value(old)) {
+		if (old)
 			mapping->nrexceptional--;
-			if (shadowp)
-				*shadowp = old;
-		}
 		mapping->nrpages++;
 
 		/* hugetlb pages do not participate in page cache accounting */
@@ -894,7 +913,7 @@ noinline int __add_to_page_cache_locked(struct page *page,
 			__inc_node_page_state(page, NR_FILE_PAGES);
 unlock:
 		xas_unlock_irq(&xas);
-	} while (xas_nomem(&xas, gfp_mask & GFP_RECLAIM_MASK));
+	} while (xas_nomem(&xas, gfp_mask));
 
 	if (xas_error(&xas))
 		goto error;
-- 
2.30.2

Re: [5.4 PATCH 0/4] Fix a CONFIG_READ_ONLY_THP_FOR_FS bug

[Greg KH]

On Mon, Jun 07, 2021 at 09:08:41PM +0100, Matthew Wilcox (Oracle) wrote:
> This experimental feature has had a few bugs, but it has enough of
> a performance effect that customers are actually asking for it to be
> enabled.  So we should apply this upstream bugfix that needs a little
> massaging to backport.  The first three patches enable the fix in the
> fourth patch.  I've run the XArray test-suite after applying these
> patches, and it continues to pass.
> 
> Matthew Wilcox (Oracle) (4):
>   mm: add thp_order
>   XArray: add xa_get_order
>   XArray: add xas_split
>   mm/filemap: fix storing to a THP shadow entry
> 
>  Documentation/core-api/xarray.rst |  16 ++-
>  include/linux/huge_mm.h           |  19 +++
>  include/linux/xarray.h            |  22 ++++
>  lib/test_xarray.c                 |  65 ++++++++++
>  lib/xarray.c                      | 208 ++++++++++++++++++++++++++++--
>  mm/filemap.c                      |  37 ++++--
>  6 files changed, 342 insertions(+), 25 deletions(-)
> 
> -- 
> 2.30.2
> 

Now queued up, thanks.

greg k-h