ceph: do not use i_wrbuffer_ref as refcount for Fb cap

We increments i_wrbuffer_ref when taking the Fb cap. This breaks
the dirty page accounting and causes looping in
__ceph_do_pending_vmtruncate, and ceph client hangs.

This bug can be reproduced occasionally by running blogbench.

Add a new field i_wb_ref to inode and dedicate it to Fb reference
counting.
Signed-off-by: Henry C Chang <henry.cy.chang@gmail.com>
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/caps.c

@@ -819,7 +819,7 @@ int __ceph_caps_used(struct ceph_inode_info *ci)
 		used |= CEPH_CAP_FILE_CACHE;
 	if (ci->i_wr_ref)
 		used |= CEPH_CAP_FILE_WR;
-	if (ci->i_wrbuffer_ref)
+	if (ci->i_wb_ref || ci->i_wrbuffer_ref)
 		used |= CEPH_CAP_FILE_BUFFER;
 	return used;
 }
@@ -1990,11 +1990,11 @@ static void __take_cap_refs(struct ceph_inode_info *ci, int got)
 	if (got & CEPH_CAP_FILE_WR)
 		ci->i_wr_ref++;
 	if (got & CEPH_CAP_FILE_BUFFER) {
-		if (ci->i_wrbuffer_ref == 0)
+		if (ci->i_wb_ref == 0)
 			ihold(&ci->vfs_inode);
-		ci->i_wrbuffer_ref++;
-		dout("__take_cap_refs %p wrbuffer %d -> %d (?)\n",
-		     &ci->vfs_inode, ci->i_wrbuffer_ref-1, ci->i_wrbuffer_ref);
+		ci->i_wb_ref++;
+		dout("__take_cap_refs %p wb %d -> %d (?)\n",
+		     &ci->vfs_inode, ci->i_wb_ref-1, ci->i_wb_ref);
 	}
 }
 
@@ -2169,12 +2169,12 @@ void ceph_put_cap_refs(struct ceph_inode_info *ci, int had)
 		if (--ci->i_rdcache_ref == 0)
 			last++;
 	if (had & CEPH_CAP_FILE_BUFFER) {
-		if (--ci->i_wrbuffer_ref == 0) {
+		if (--ci->i_wb_ref == 0) {
 			last++;
 			put++;
 		}
-		dout("put_cap_refs %p wrbuffer %d -> %d (?)\n",
-		     inode, ci->i_wrbuffer_ref+1, ci->i_wrbuffer_ref);
+		dout("put_cap_refs %p wb %d -> %d (?)\n",
+		     inode, ci->i_wb_ref+1, ci->i_wb_ref);
 	}
 	if (had & CEPH_CAP_FILE_WR)
 		if (--ci->i_wr_ref == 0) {

fs/ceph/inode.c

@@ -355,6 +355,7 @@ struct inode *ceph_alloc_inode(struct super_block *sb)
 	ci->i_rd_ref = 0;
 	ci->i_rdcache_ref = 0;
 	ci->i_wr_ref = 0;
+	ci->i_wb_ref = 0;
 	ci->i_wrbuffer_ref = 0;
 	ci->i_wrbuffer_ref_head = 0;
 	ci->i_shared_gen = 0;

fs/ceph/super.h

@@ -293,7 +293,7 @@ struct ceph_inode_info {
 
 	/* held references to caps */
 	int i_pin_ref;
-	int i_rd_ref, i_rdcache_ref, i_wr_ref;
+	int i_rd_ref, i_rdcache_ref, i_wr_ref, i_wb_ref;
 	int i_wrbuffer_ref, i_wrbuffer_ref_head;
 	u32 i_shared_gen;       /* increment each time we get FILE_SHARED */
 	u32 i_rdcache_gen;      /* incremented each time we get FILE_CACHE. */