splice: fix generic_file_splice_read() race with page invalidation

If a page was invalidated during splicing from file to a pipe, then
generic_file_splice_read() could return a short or zero count.

This manifested itself in rare I/O errors seen on nfs exported fuse
filesystems.  This is because nfsd uses splice_direct_to_actor() to read
files, and fuse uses invalidate_inode_pages2() to invalidate stale data on
open.

Fix by redoing the page find/create if it was found to be truncated
(invalidated).

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 13 insertions, 4 deletions

diff --git a/fs/splice.c b/fs/splice.c
index aa5f6f60b305..399442179d89 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -379,13 +379,22 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
                                 lock_page(page);
 
                         /*
-                         * page was truncated, stop here. if this isn't the
-                         * first page, we'll just complete what we already
-                         * added
+                         * Page was truncated, or invalidated by the
+                         * filesystem.  Redo the find/create, but this time the
+                         * page is kept locked, so there's no chance of another
+                         * race with truncate/invalidate.
                          */
                         if (!page->mapping) {
                                 unlock_page(page);
-                                break;
+                                page = find_or_create_page(mapping, index,
+                                                mapping_gfp_mask(mapping));
+
+                                if (!page) {
+                                        error = -ENOMEM;
+                                        break;
+                                }
+                                page_cache_release(pages[page_nr]);
+                                pages[page_nr] = page;
                         }
                         /*
                          * page was already under io and is now done, great