FAILED: patch "[PATCH] mm, thp: fix incorrect unmap behavior for private pages" failed to apply to 5.14-stable tree

The patch below does not apply to the 5.14-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 8468e937df1f31411d1e127fa38db064af051fe5 Mon Sep 17 00:00:00 2001
From: Rongwei Wang <[email protected]>
Date: Fri, 5 Nov 2021 13:43:44 -0700
Subject: [PATCH] mm, thp: fix incorrect unmap behavior for private pages

When truncating pagecache on file THP, the private pages of a process should not be unmapped mapping. This incorrect behavior on a dynamic shared libraries which will cause related processes to happen core dump.

A simple test for a DSO (Prerequisite is the DSO mapped in file THP):

    int main(int argc, char *argv[])
    {
	int fd;

	fd = open(argv[1], O_WRONLY);
	if (fd < 0) {
		perror("open");
	}

	close(fd);
	return 0;
    }

The test only to open a target DSO, and do nothing. But this operation will lead one or more process to happen core dump. This patch mainly to fix this bug.

index 9ec3cfca3b1a..e0df1536eb69 100644
@@ -857,8 +857,17 @@ static int do_dentry_open(struct file *f,
 		 */
 		smp_mb();
 		if (filemap_nr_thps(inode->i_mapping)) {
+			struct address_space *mapping = inode->i_mapping;
+
 			filemap_invalidate_lock(inode->i_mapping);
-			truncate_pagecache(inode, 0);
+			/*
+			 * unmap_mapping_range just need to be called once
+			 * here, because the private pages is not need to be
+			 * unmapped mapping (e.g. data segment of dynamic
+			 * shared libraries here).
+			 */
+			unmap_mapping_range(mapping, 0, 0, 0);
+			truncate_inode_pages(mapping, 0);
 			filemap_invalidate_unlock(inode->i_mapping);
 		}
 	}