[bug] userspace hitting sporadic SIGBUS on xfs (Power9, ppc64le), v4.19 and later

[Christoph Hellwig]

Please try the patch below:

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 512856a88106..340c15400423 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -28,6 +28,7 @@
 struct iomap_page {
 	atomic_t		read_count;
 	atomic_t		write_count;
+	spinlock_t		uptodate_lock;
 	DECLARE_BITMAP(uptodate, PAGE_SIZE / 512);
 };
 
@@ -51,6 +52,7 @@ iomap_page_create(struct inode *inode, struct page *page)
 	iop = kmalloc(sizeof(*iop), GFP_NOFS | __GFP_NOFAIL);
 	atomic_set(&iop->read_count, 0);
 	atomic_set(&iop->write_count, 0);
+	spin_lock_init(&iop->uptodate_lock);
 	bitmap_zero(iop->uptodate, PAGE_SIZE / SECTOR_SIZE);
 
 	/*
@@ -139,25 +141,38 @@ iomap_adjust_read_range(struct inode *inode, struct iomap_page *iop,
 }
 
 static void
-iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len)
+iomap_iop_set_range_uptodate(struct page *page, unsigned off, unsigned len)
 {
 	struct iomap_page *iop = to_iomap_page(page);
 	struct inode *inode = page->mapping->host;
 	unsigned first = off >> inode->i_blkbits;
 	unsigned last = (off + len - 1) >> inode->i_blkbits;
-	unsigned int i;
 	bool uptodate = true;
+	unsigned long flags;
+	unsigned int i;
 
-	if (iop) {
-		for (i = 0; i < PAGE_SIZE / i_blocksize(inode); i++) {
-			if (i >= first && i <= last)
-				set_bit(i, iop->uptodate);
-			else if (!test_bit(i, iop->uptodate))
-				uptodate = false;
-		}
+	spin_lock_irqsave(&iop->uptodate_lock, flags);
+	for (i = 0; i < PAGE_SIZE / i_blocksize(inode); i++) {
+		if (i >= first && i <= last)
+			set_bit(i, iop->uptodate);
+		else if (!test_bit(i, iop->uptodate))
+			uptodate = false;
 	}
 
-	if (uptodate && !PageError(page))
+	if (uptodate)
+		SetPageUptodate(page);
+	spin_unlock_irqrestore(&iop->uptodate_lock, flags);
+}
+
+static void
+iomap_set_range_uptodate(struct page *page, unsigned off, unsigned len)
+{
+	if (PageError(page))
+		return;
+
+	if (page_has_private(page))
+		iomap_iop_set_range_uptodate(page, off, len);
+	else
 		SetPageUptodate(page);
 }