NFS: Fix an unstable write data integrity race

Commit 2c61be0a9478258f77b66208a0c4b1f5f8161c3c (NFS: Ensure that the WRITE
and COMMIT RPC calls are always uninterruptible) exposed a race on file
close. In order to ensure correct close-to-open behaviour, we want to wait
for all outstanding background commit operations to complete.

This patch adds an inode flag that indicates if a commit operation is under
way, and provides a mechanism to allow ->write_inode() to wait for its
completion if this is a data integrity flush.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

2 files changed, 33 insertions, 4 deletions

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index de38d63aa920..ccde2aeb3fec 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1201,6 +1201,25 @@ int nfs_writeback_done(struct rpc_task *task, struct nfs_write_data *data)
 
 
 #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
+static int nfs_commit_set_lock(struct nfs_inode *nfsi, int may_wait)
+{
+        if (!test_and_set_bit(NFS_INO_COMMIT, &nfsi->flags))
+                return 1;
+        if (may_wait && !out_of_line_wait_on_bit_lock(&nfsi->flags,
+                                NFS_INO_COMMIT, nfs_wait_bit_killable,
+                                TASK_KILLABLE))
+                return 1;
+        return 0;
+}
+
+static void nfs_commit_clear_lock(struct nfs_inode *nfsi)
+{
+        clear_bit(NFS_INO_COMMIT, &nfsi->flags);
+        smp_mb__after_clear_bit();
+        wake_up_bit(&nfsi->flags, NFS_INO_COMMIT);
+}
+
+
 static void nfs_commitdata_release(void *data)
 {
         struct nfs_write_data *wdata = data;
@@ -1262,8 +1281,6 @@ static int nfs_commit_rpcsetup(struct list_head *head,
         task = rpc_run_task(&task_setup_data);
         if (IS_ERR(task))
                 return PTR_ERR(task);
-        if (how & FLUSH_SYNC)
-                rpc_wait_for_completion_task(task);
         rpc_put_task(task);
         return 0;
 }
@@ -1294,6 +1311,7 @@ nfs_commit_list(struct inode *inode, struct list_head *head, int how)
                                 BDI_RECLAIMABLE);
                 nfs_clear_page_tag_locked(req);
         }
+        nfs_commit_clear_lock(NFS_I(inode));
         return -ENOMEM;
 }
 
@@ -1349,6 +1367,7 @@ static void nfs_commit_release(void *calldata)
         next:
                 nfs_clear_page_tag_locked(req);
         }
+        nfs_commit_clear_lock(NFS_I(data->inode));
         nfs_commitdata_release(calldata);
 }
 
@@ -1363,8 +1382,11 @@ static const struct rpc_call_ops nfs_commit_ops = {
 static int nfs_commit_inode(struct inode *inode, int how)
 {
         LIST_HEAD(head);
-        int res;
+        int may_wait = how & FLUSH_SYNC;
+        int res = 0;
 
+        if (!nfs_commit_set_lock(NFS_I(inode), may_wait))
+                goto out;
         spin_lock(&inode->i_lock);
         res = nfs_scan_commit(inode, &head, 0, 0);
         spin_unlock(&inode->i_lock);
@@ -1372,7 +1394,13 @@ static int nfs_commit_inode(struct inode *inode, int how)
                 int error = nfs_commit_list(inode, &head, how);
                 if (error < 0)
                         return error;
-        }
+                if (may_wait)
+                        wait_on_bit(&NFS_I(inode)->flags, NFS_INO_COMMIT,
+                                        nfs_wait_bit_killable,
+                                        TASK_KILLABLE);
+        } else
+                nfs_commit_clear_lock(NFS_I(inode));
+out:
         return res;
 }
 
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index 1a0b85aa151e..07ce4609fe50 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -209,6 +209,7 @@ struct nfs_inode {
 #define NFS_INO_FLUSHING        (4)             /* inode is flushing out data */
 #define NFS_INO_FSCACHE         (5)             /* inode can be cached by FS-Cache */
 #define NFS_INO_FSCACHE_LOCK    (6)             /* FS-Cache cookie management lock */
+#define NFS_INO_COMMIT          (7)             /* inode is committing unstable writes */
 
 static inline struct nfs_inode *NFS_I(const struct inode *inode)
 {