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>

3 files changed, 10 insertions, 9 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 9fa08662a88d..2a5404c1c42f 100644
--- a/fs/ceph/caps.c
+++ b/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) {
diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 03d6dafda61f..70b6a4839c38 100644
--- a/fs/ceph/inode.c
+++ b/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;
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index b1f1b8bb1271..f5cabefa98dc 100644
--- a/fs/ceph/super.h
+++ b/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. */