UBIFS: fix zero-length truncations

Always allow truncations to zero, even if budgeting thinks there
is no space. UBIFS reserves some space for deletions anyway.

Otherwise, the following happans:
1. create a file, and write as much as possible there, until ENOSPC
2. truncate the file, which fails with ENOSPC, which is not good.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

1 files changed, 16 insertions, 4 deletions

diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 4071d1cae29f..3d698e2022b1 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -793,7 +793,7 @@ static int do_truncation(struct ubifs_info *c, struct inode *inode,
         int err;
         struct ubifs_budget_req req;
         loff_t old_size = inode->i_size, new_size = attr->ia_size;
-        int offset = new_size & (UBIFS_BLOCK_SIZE - 1);
+        int offset = new_size & (UBIFS_BLOCK_SIZE - 1), budgeted = 1;
         struct ubifs_inode *ui = ubifs_inode(inode);
 
         dbg_gen("ino %lu, size %lld -> %lld", inode->i_ino, old_size, new_size);
@@ -811,8 +811,15 @@ static int do_truncation(struct ubifs_info *c, struct inode *inode,
         /* A funny way to budget for truncation node */
         req.dirtied_ino_d = UBIFS_TRUN_NODE_SZ;
         err = ubifs_budget_space(c, &req);
-        if (err)
-                return err;
+        if (err) {
+                /*
+                 * Treat truncations to zero as deletion and always allow them,
+                 * just like we do for '->unlink()'.
+                 */
+                if (new_size || err != -ENOSPC)
+                        return err;
+                budgeted = 0;
+        }
 
         err = vmtruncate(inode, new_size);
         if (err)
@@ -869,7 +876,12 @@ static int do_truncation(struct ubifs_info *c, struct inode *inode,
         err = ubifs_jnl_truncate(c, inode, old_size, new_size);
         mutex_unlock(&ui->ui_mutex);
 out_budg:
-        ubifs_release_budget(c, &req);
+        if (budgeted)
+                ubifs_release_budget(c, &req);
+        else {
+                c->nospace = c->nospace_rp = 0;
+                smp_wmb();
+        }
         return err;
 }