afs: check function return

Static analysis reports this problem

write.c:773:29: warning: Assigned value is garbage or undefined
  mapping->writeback_index = next;
                           ^ ~~~~
The call to afs_writepages_region() can return without setting
next.  So check the function return before using next.

Changes:
 ver #2:
   - Need to fix the range_cyclic case also[1].

Fixes: e87b03f5830e ("afs: Prepare for use of THPs")
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://lore.kernel.org/r/20210430155031.3287870-1-trix@redhat.com
Link: https://lore.kernel.org/r/CAB9dFdvHsLsw7CMnB+4cgciWDSqVjuij4mH3TaXnHQB8sz5rHw@mail.gmail.com/
Link: https://lore.kernel.org/r/162609464716.3133237.10354897554363093252.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/162610727640.3408253.8687445613469681311.stgit@warthog.procyon.org.uk/

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 3104b62..1ed62e0 100644 (file)
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -771,13 +771,19 @@ int afs_writepages(struct address_space *mapping,
        if (wbc->range_cyclic) {
                start = mapping->writeback_index * PAGE_SIZE;
                ret = afs_writepages_region(mapping, wbc, start, LLONG_MAX, &next);
-               if (start > 0 && wbc->nr_to_write > 0 && ret == 0)
-                       ret = afs_writepages_region(mapping, wbc, 0, start,
-                                                   &next);
-               mapping->writeback_index = next / PAGE_SIZE;
+               if (ret == 0) {
+                       mapping->writeback_index = next / PAGE_SIZE;
+                       if (start > 0 && wbc->nr_to_write > 0) {
+                               ret = afs_writepages_region(mapping, wbc, 0,
+                                                           start, &next);
+                               if (ret == 0)
+                                       mapping->writeback_index =
+                                               next / PAGE_SIZE;
+                       }
+               }
        } else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
                ret = afs_writepages_region(mapping, wbc, 0, LLONG_MAX, &next);
-               if (wbc->nr_to_write > 0)
+               if (wbc->nr_to_write > 0 && ret == 0)
                        mapping->writeback_index = next;
        } else {
                ret = afs_writepages_region(mapping, wbc,