ceph: set i_head_snapc when getting CEPH_CAP_FILE_WR reference

In most cases that snap context is needed, we are holding
reference of CEPH_CAP_FILE_WR. So we can set ceph inode's
i_head_snapc when getting the CEPH_CAP_FILE_WR reference,
and make codes get snap context from i_head_snapc. This makes
the code simpler.

Another benefit of this change is that we can handle snap
notification more elegantly. Especially when snap context
is updated while someone else is doing write. The old queue
cap_snap code may set cap_snap's context to ether the old
context or the new snap context, depending on if i_head_snapc
is set. The new queue capp_snap code always set cap_snap's
context to the old snap context.

Signed-off-by: Yan, Zheng <zyan@redhat.com>

1 files changed, 14 insertions, 23 deletions

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index ccc4325aa5c5..5f53ac0d9d7c 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -87,17 +87,21 @@ static int ceph_set_page_dirty(struct page *page)
         inode = mapping->host;
         ci = ceph_inode(inode);
 
-        /*
-         * Note that we're grabbing a snapc ref here without holding
-         * any locks!
-         */
-        snapc = ceph_get_snap_context(ci->i_snap_realm->cached_context);
-
         /* dirty the head */
         spin_lock(&ci->i_ceph_lock);
-        if (ci->i_head_snapc == NULL)
-                ci->i_head_snapc = ceph_get_snap_context(snapc);
-        ++ci->i_wrbuffer_ref_head;
+        BUG_ON(ci->i_wr_ref == 0); // caller should hold Fw reference
+        if (__ceph_have_pending_cap_snap(ci)) {
+                struct ceph_cap_snap *capsnap =
+                                list_last_entry(&ci->i_cap_snaps,
+                                                struct ceph_cap_snap,
+                                                ci_item);
+                snapc = ceph_get_snap_context(capsnap->context);
+                capsnap->dirty_pages++;
+        } else {
+                BUG_ON(!ci->i_head_snapc);
+                snapc = ceph_get_snap_context(ci->i_head_snapc);
+                ++ci->i_wrbuffer_ref_head;
+        }
         if (ci->i_wrbuffer_ref == 0)
                 ihold(inode);
         ++ci->i_wrbuffer_ref;
@@ -1033,7 +1037,6 @@ static int ceph_update_writeable_page(struct file *file,
 {
         struct inode *inode = file_inode(file);
         struct ceph_inode_info *ci = ceph_inode(inode);
-        struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;
         loff_t page_off = pos & PAGE_CACHE_MASK;
         int pos_in_page = pos & ~PAGE_CACHE_MASK;
         int end_in_page = pos_in_page + len;
@@ -1045,10 +1048,6 @@ retry_locked:
         /* writepages currently holds page lock, but if we change that later, */
         wait_on_page_writeback(page);
 
-        /* check snap context */
-        BUG_ON(!ci->i_snap_realm);
-        down_read(&mdsc->snap_rwsem);
-        BUG_ON(!ci->i_snap_realm->cached_context);
         snapc = page_snap_context(page);
         if (snapc && snapc != ci->i_head_snapc) {
                 /*
@@ -1056,7 +1055,6 @@ retry_locked:
                  * context!  is it writeable now?
                  */
                 oldest = get_oldest_context(inode, NULL);
-                up_read(&mdsc->snap_rwsem);
 
                 if (snapc->seq > oldest->seq) {
                         ceph_put_snap_context(oldest);
@@ -1113,7 +1111,6 @@ retry_locked:
         }
 
         /* we need to read it. */
-        up_read(&mdsc->snap_rwsem);
         r = readpage_nounlock(file, page);
         if (r < 0)
                 goto fail_nosnap;
@@ -1158,16 +1155,13 @@ static int ceph_write_begin(struct file *file, struct address_space *mapping,
 
 /*
  * we don't do anything in here that simple_write_end doesn't do
- * except adjust dirty page accounting and drop read lock on
- * mdsc->snap_rwsem.
+ * except adjust dirty page accounting
  */
 static int ceph_write_end(struct file *file, struct address_space *mapping,
                           loff_t pos, unsigned len, unsigned copied,
                           struct page *page, void *fsdata)
 {
         struct inode *inode = file_inode(file);
-        struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
-        struct ceph_mds_client *mdsc = fsc->mdsc;
         unsigned from = pos & (PAGE_CACHE_SIZE - 1);
         int check_cap = 0;
 
@@ -1189,7 +1183,6 @@ static int ceph_write_end(struct file *file, struct address_space *mapping,
         set_page_dirty(page);
 
         unlock_page(page);
-        up_read(&mdsc->snap_rwsem);
         page_cache_release(page);
 
         if (check_cap)
@@ -1315,7 +1308,6 @@ static int ceph_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
         struct inode *inode = file_inode(vma->vm_file);
         struct ceph_inode_info *ci = ceph_inode(inode);
         struct ceph_file_info *fi = vma->vm_file->private_data;
-        struct ceph_mds_client *mdsc = ceph_inode_to_client(inode)->mdsc;
         struct page *page = vmf->page;
         loff_t off = page_offset(page);
         loff_t size = i_size_read(inode);
@@ -1374,7 +1366,6 @@ static int ceph_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
         if (ret == 0) {
                 /* success.  we'll keep the page locked. */
                 set_page_dirty(page);
-                up_read(&mdsc->snap_rwsem);
                 ret = VM_FAULT_LOCKED;
         } else {
                 if (ret == -ENOMEM)