ext4: don't allow ext4_free_blocks() to fail due to ENOMEM

The filesystem should not be marked inconsistent if ext4_free_blocks()
is not able to allocate memory.  Unfortunately some callers (most
notably ext4_truncate) don't have a way to reflect an error back up to
the VFS.  And even if we did, most userspace applications won't deal
with most system calls returning ENOMEM anyway.

Reported-by: Nagachandra P <nagachandra@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org

1 files changed, 8 insertions, 3 deletions

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index a9ff5e5137ca..4bbbf13bd743 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4740,11 +4740,16 @@ do_more:
                  * blocks being freed are metadata. these blocks shouldn't
                  * be used until this transaction is committed
                  */
+        retry:
                 new_entry = kmem_cache_alloc(ext4_free_data_cachep, GFP_NOFS);
                 if (!new_entry) {
-                        ext4_mb_unload_buddy(&e4b);
-                        err = -ENOMEM;
-                        goto error_return;
+                        /*
+                         * We use a retry loop because
+                         * ext4_free_blocks() is not allowed to fail.
+                         */
+                        cond_resched();
+                        congestion_wait(BLK_RW_ASYNC, HZ/50);
+                        goto retry;
                 }
                 new_entry->efd_start_cluster = bit;
                 new_entry->efd_group = block_group;