ceph: take snap_rwsem when accessing snap realm's cached_context

When ceph inode's i_head_snapc is NULL, __ceph_mark_dirty_caps()
accesses snap realm's cached_context. So we need take read lock
of snap_rwsem.

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

1 files changed, 39 insertions, 6 deletions

diff --git a/fs/ceph/xattr.c b/fs/ceph/xattr.c
index cd7ffad4041d..c6f7d9b82085 100644
--- a/fs/ceph/xattr.c
+++ b/fs/ceph/xattr.c
@@ -911,6 +911,7 @@ int __ceph_setxattr(struct dentry *dentry, const char *name,
         struct inode *inode = d_inode(dentry);
         struct ceph_vxattr *vxattr;
         struct ceph_inode_info *ci = ceph_inode(inode);
+        struct ceph_mds_client *mdsc = ceph_sb_to_client(dentry->d_sb)->mdsc;
         int issued;
         int err;
         int dirty = 0;
@@ -920,6 +921,7 @@ int __ceph_setxattr(struct dentry *dentry, const char *name,
         char *newval = NULL;
         struct ceph_inode_xattr *xattr = NULL;
         int required_blob_size;
+        bool lock_snap_rwsem = false;
 
         if (!ceph_is_valid_xattr(name))
                 return -EOPNOTSUPP;
@@ -951,9 +953,20 @@ int __ceph_setxattr(struct dentry *dentry, const char *name,
         spin_lock(&ci->i_ceph_lock);
 retry:
         issued = __ceph_caps_issued(ci, NULL);
-        dout("setxattr %p issued %s\n", inode, ceph_cap_string(issued));
         if (ci->i_xattrs.version == 0 || !(issued & CEPH_CAP_XATTR_EXCL))
                 goto do_sync;
+
+        if (!lock_snap_rwsem && !ci->i_head_snapc) {
+                lock_snap_rwsem = true;
+                if (!down_read_trylock(&mdsc->snap_rwsem)) {
+                        spin_unlock(&ci->i_ceph_lock);
+                        down_read(&mdsc->snap_rwsem);
+                        spin_lock(&ci->i_ceph_lock);
+                        goto retry;
+                }
+        }
+
+        dout("setxattr %p issued %s\n", inode, ceph_cap_string(issued));
         __build_xattrs(inode);
 
         required_blob_size = __get_required_blob_size(ci, name_len, val_len);
@@ -966,7 +979,7 @@ retry:
                 dout(" preaallocating new blob size=%d\n", required_blob_size);
                 blob = ceph_buffer_new(required_blob_size, GFP_NOFS);
                 if (!blob)
-                        goto out;
+                        goto do_sync_unlocked;
                 spin_lock(&ci->i_ceph_lock);
                 if (ci->i_xattrs.prealloc_blob)
                         ceph_buffer_put(ci->i_xattrs.prealloc_blob);
@@ -984,6 +997,8 @@ retry:
         }
 
         spin_unlock(&ci->i_ceph_lock);
+        if (lock_snap_rwsem)
+                up_read(&mdsc->snap_rwsem);
         if (dirty)
                 __mark_inode_dirty(inode, dirty);
         return err;
@@ -991,6 +1006,8 @@ retry:
 do_sync:
         spin_unlock(&ci->i_ceph_lock);
 do_sync_unlocked:
+        if (lock_snap_rwsem)
+                up_read(&mdsc->snap_rwsem);
         err = ceph_sync_setxattr(dentry, name, value, size, flags);
 out:
         kfree(newname);
@@ -1044,10 +1061,12 @@ int __ceph_removexattr(struct dentry *dentry, const char *name)
         struct inode *inode = d_inode(dentry);
         struct ceph_vxattr *vxattr;
         struct ceph_inode_info *ci = ceph_inode(inode);
+        struct ceph_mds_client *mdsc = ceph_sb_to_client(dentry->d_sb)->mdsc;
         int issued;
         int err;
         int required_blob_size;
         int dirty;
+        bool lock_snap_rwsem = false;
 
         if (!ceph_is_valid_xattr(name))
                 return -EOPNOTSUPP;
@@ -1064,10 +1083,21 @@ int __ceph_removexattr(struct dentry *dentry, const char *name)
         spin_lock(&ci->i_ceph_lock);
 retry:
         issued = __ceph_caps_issued(ci, NULL);
-        dout("removexattr %p issued %s\n", inode, ceph_cap_string(issued));
-
         if (ci->i_xattrs.version == 0 || !(issued & CEPH_CAP_XATTR_EXCL))
                 goto do_sync;
+
+        if (!lock_snap_rwsem && !ci->i_head_snapc) {
+                lock_snap_rwsem = true;
+                if (!down_read_trylock(&mdsc->snap_rwsem)) {
+                        spin_unlock(&ci->i_ceph_lock);
+                        down_read(&mdsc->snap_rwsem);
+                        spin_lock(&ci->i_ceph_lock);
+                        goto retry;
+                }
+        }
+
+        dout("removexattr %p issued %s\n", inode, ceph_cap_string(issued));
+
         __build_xattrs(inode);
 
         required_blob_size = __get_required_blob_size(ci, 0, 0);
@@ -1080,7 +1110,7 @@ retry:
                 dout(" preaallocating new blob size=%d\n", required_blob_size);
                 blob = ceph_buffer_new(required_blob_size, GFP_NOFS);
                 if (!blob)
-                        goto out;
+                        goto do_sync_unlocked;
                 spin_lock(&ci->i_ceph_lock);
                 if (ci->i_xattrs.prealloc_blob)
                         ceph_buffer_put(ci->i_xattrs.prealloc_blob);
@@ -1094,14 +1124,17 @@ retry:
         ci->i_xattrs.dirty = true;
         inode->i_ctime = CURRENT_TIME;
         spin_unlock(&ci->i_ceph_lock);
+        if (lock_snap_rwsem)
+                up_read(&mdsc->snap_rwsem);
         if (dirty)
                 __mark_inode_dirty(inode, dirty);
         return err;
 do_sync:
         spin_unlock(&ci->i_ceph_lock);
 do_sync_unlocked:
+        if (lock_snap_rwsem)
+                up_read(&mdsc->snap_rwsem);
         err = ceph_send_removexattr(dentry, name);
-out:
         return err;
 }