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Subject[PATCH] UBIFS: fix zero-length truncations
Date
From: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

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>
---
fs/ubifs/dir.c | 1 -
fs/ubifs/file.c | 20 ++++++++++++++++----
2 files changed, 16 insertions(+), 5 deletions(-)
diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c
index 5c96f1f..2b267c9 100644
--- a/fs/ubifs/dir.c
+++ b/fs/ubifs/dir.c
@@ -587,7 +587,6 @@ static int ubifs_unlink(struct inode *dir, struct dentry *dentry)
if (err) {
if (err != -ENOSPC)
return err;
- err = 0;
budgeted = 0;
}

diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index 4071d1c..3d698e2 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;
}

--
1.5.4.1


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