NFS: Fix unstable write completion

We do want to respect the FLUSH_SYNC argument to nfs_commit_inode() to
ensure that all outstanding COMMIT requests to the inode in question are
complete. Currently we may exit early from both nfs_commit_inode() and
nfs_write_inode() even if there are COMMIT requests in flight, or unstable
writes on the commit list.

In order to get the right semantics w.r.t. sync_inode(), we don't need
to have nfs_commit_inode() reset the inode dirty flags when called from
nfs_wb_page() and/or nfs_wb_all(). We just need to ensure that
nfs_write_inode() leaves them in the right state if there are outstanding
commits, or stable pages.

Reported-by: Scott Mayhew <smayhew@redhat.com>
Fixes: dc4fd9ab01ab ("nfs: don't wait on commit in nfs_commit_inode()...")
Cc: stable@vger.kernel.org # v4.14+
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 43 insertions, 40 deletions

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index 7428a669d7a7..e7d8ceae8f26 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1876,40 +1876,43 @@ int nfs_generic_commit_list(struct inode *inode, struct list_head *head,
         return status;
 }
 
-int nfs_commit_inode(struct inode *inode, int how)
+static int __nfs_commit_inode(struct inode *inode, int how,
+                struct writeback_control *wbc)
 {
         LIST_HEAD(head);
         struct nfs_commit_info cinfo;
         int may_wait = how & FLUSH_SYNC;
-        int error = 0;
-        int res;
+        int ret, nscan;
 
         nfs_init_cinfo_from_inode(&cinfo, inode);
         nfs_commit_begin(cinfo.mds);
-        res = nfs_scan_commit(inode, &head, &cinfo);
-        if (res)
-                error = nfs_generic_commit_list(inode, &head, how, &cinfo);
+        for (;;) {
+                ret = nscan = nfs_scan_commit(inode, &head, &cinfo);
+                if (ret <= 0)
+                        break;
+                ret = nfs_generic_commit_list(inode, &head, how, &cinfo);
+                if (ret < 0)
+                        break;
+                ret = 0;
+                if (wbc && wbc->sync_mode == WB_SYNC_NONE) {
+                        if (nscan < wbc->nr_to_write)
+                                wbc->nr_to_write -= nscan;
+                        else
+                                wbc->nr_to_write = 0;
+                }
+                if (nscan < INT_MAX)
+                        break;
+                cond_resched();
+        }
         nfs_commit_end(cinfo.mds);
-        if (res == 0)
-                return res;
-        if (error < 0)
-                goto out_error;
-        if (!may_wait)
-                goto out_mark_dirty;
-        error = wait_on_commit(cinfo.mds);
-        if (error < 0)
-                return error;
-        return res;
-out_error:
-        res = error;
-        /* Note: If we exit without ensuring that the commit is complete,
-         * we must mark the inode as dirty. Otherwise, future calls to
-         * sync_inode() with the WB_SYNC_ALL flag set will fail to ensure
-         * that the data is on the disk.
-         */
-out_mark_dirty:
-        __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
-        return res;
+        if (ret || !may_wait)
+                return ret;
+        return wait_on_commit(cinfo.mds);
+}
+
+int nfs_commit_inode(struct inode *inode, int how)
+{
+        return __nfs_commit_inode(inode, how, NULL);
 }
 EXPORT_SYMBOL_GPL(nfs_commit_inode);
 
@@ -1919,11 +1922,11 @@ int nfs_write_inode(struct inode *inode, struct writeback_control *wbc)
         int flags = FLUSH_SYNC;
         int ret = 0;
 
-        /* no commits means nothing needs to be done */
-        if (!atomic_long_read(&nfsi->commit_info.ncommit))
-                return ret;
-
         if (wbc->sync_mode == WB_SYNC_NONE) {
+                /* no commits means nothing needs to be done */
+                if (!atomic_long_read(&nfsi->commit_info.ncommit))
+                        goto check_requests_outstanding;
+
                 /* Don't commit yet if this is a non-blocking flush and there
                  * are a lot of outstanding writes for this mapping.
                  */
@@ -1934,16 +1937,16 @@ int nfs_write_inode(struct inode *inode, struct writeback_control *wbc)
                 flags = 0;
         }
 
-        ret = nfs_commit_inode(inode, flags);
-        if (ret >= 0) {
-                if (wbc->sync_mode == WB_SYNC_NONE) {
-                        if (ret < wbc->nr_to_write)
-                                wbc->nr_to_write -= ret;
-                        else
-                                wbc->nr_to_write = 0;
-                }
-                return 0;
-        }
+        ret = __nfs_commit_inode(inode, flags, wbc);
+        if (!ret) {
+                if (flags & FLUSH_SYNC)
+                        return 0;
+        } else if (atomic_long_read(&nfsi->commit_info.ncommit))
+                goto out_mark_dirty;
+
+check_requests_outstanding:
+        if (!atomic_read(&nfsi->commit_info.rpcs_out))
+                return ret;
 out_mark_dirty:
         __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
         return ret;