fs: __generic_file_splice_read retry lookup on AOP_TRUNCATED_PAGE

During testing, I discovered that __generic_file_splice_read() returns
0 (EOF) when aops->readpage fails with AOP_TRUNCATED_PAGE on the first
page of a single/multi-page splice read operation. This EOF return code
causes the userspace test to (correctly) report a zero-length read error
when it was expecting otherwise.

The current strategy of returning a partial non-zero read when ->readpage
returns AOP_TRUNCATED_PAGE works only when the failed page is not the
first of the lot being processed.

This patch attempts to retry lookup and call ->readpage again on pages
that had previously failed with AOP_TRUNCATED_PAGE. With this patch, my
tests pass and I haven't noticed any unwanted side effects.

This version removes the thrice-retry loop and instead indefinitely
retries lookups on AOP_TRUNCATED_PAGE errors from ->readpage. This
behavior is now similar to do_generic_file_read().

Signed-off-by: Abhi Das <adas@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Bob Peterson <rpeterso@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/splice.c b/fs/splice.c
index 4cf700d50b4037e6c334b0647cdb81b816f9ef65..82bc0d64fc38d538b6482adf7d5d279318405069 100644 (file)
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -415,6 +415,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
                         */
                        if (!page->mapping) {
                                unlock_page(page);
+retry_lookup:
                                page = find_or_create_page(mapping, index,
                                                mapping_gfp_mask(mapping));
 
@@ -439,13 +440,10 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
                        error = mapping->a_ops->readpage(in, page);
                        if (unlikely(error)) {
                                /*
-                                * We really should re-lookup the page here,
-                                * but it complicates things a lot. Instead
-                                * lets just do what we already stored, and
-                                * we'll get it the next time we are called.
+                                * Re-lookup the page
                                 */
                                if (error == AOP_TRUNCATED_PAGE)
-                                       error = 0;
+                                       goto retry_lookup;
 
                                break;
                        }