ceph: take i_mutex before getting Fw cap

There is deadlock as illustrated bellow. The fix is taking i_mutex
before getting Fw cap reference.

      write                    truncate                 MDS
---------------------     --------------------      --------------
get Fw cap
                          lock i_mutex
lock i_mutex (blocked)
                          request setattr.size  ->
                                                <-   revoke Fw cap

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Alex Elder <elder@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>

2 files changed, 13 insertions, 12 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index f9563108d189..da0f9b8a3bcb 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -2052,6 +2052,13 @@ static int try_get_cap_refs(struct ceph_inode_info *ci, int need, int want,
                 goto out;
         }
 
+        /* finish pending truncate */
+        while (ci->i_truncate_pending) {
+                spin_unlock(&ci->i_ceph_lock);
+                __ceph_do_pending_vmtruncate(inode, !(need & CEPH_CAP_FILE_WR));
+                spin_lock(&ci->i_ceph_lock);
+        }
+
         if (need & CEPH_CAP_FILE_WR) {
                 if (endoff >= 0 && endoff > (loff_t)ci->i_max_size) {
                         dout("get_cap_refs %p endoff %llu > maxsize %llu\n",
@@ -2073,12 +2080,6 @@ static int try_get_cap_refs(struct ceph_inode_info *ci, int need, int want,
         }
         have = __ceph_caps_issued(ci, &implemented);
 
-        /*
-         * disallow writes while a truncate is pending
-         */
-        if (ci->i_truncate_pending)
-                have &= ~CEPH_CAP_FILE_WR;
-
         if ((have & need) == need) {
                 /*
                  * Look at (implemented & ~have & not) so that we keep waiting
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index a65acf355384..dd44f3593992 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -651,7 +651,6 @@ static ssize_t ceph_aio_read(struct kiocb *iocb, const struct iovec *iov,
         dout("aio_read %p %llx.%llx %llu~%u trying to get caps on %p\n",
              inode, ceph_vinop(inode), pos, (unsigned)len, inode);
 again:
-        __ceph_do_pending_vmtruncate(inode, true);
         if (fi->fmode & CEPH_FILE_MODE_LAZY)
                 want = CEPH_CAP_FILE_CACHE | CEPH_CAP_FILE_LAZYIO;
         else
@@ -728,7 +727,7 @@ retry_snap:
                 ret = -ENOSPC;
                 goto out;
         }
-        __ceph_do_pending_vmtruncate(inode, true);
+        mutex_lock(&inode->i_mutex);
         dout("aio_write %p %llx.%llx %llu~%u getting caps. i_size %llu\n",
              inode, ceph_vinop(inode), pos, (unsigned)iov->iov_len,
              inode->i_size);
@@ -737,8 +736,10 @@ retry_snap:
         else
                 want = CEPH_CAP_FILE_BUFFER;
         ret = ceph_get_caps(ci, CEPH_CAP_FILE_WR, want, &got, endoff);
-        if (ret < 0)
-                goto out_put;
+        if (ret < 0) {
+                mutex_unlock(&inode->i_mutex);
+                goto out;
+        }
 
         dout("aio_write %p %llx.%llx %llu~%u  got cap refs on %s\n",
              inode, ceph_vinop(inode), pos, (unsigned)iov->iov_len,
@@ -748,10 +749,10 @@ retry_snap:
             (iocb->ki_filp->f_flags & O_DIRECT) ||
             (inode->i_sb->s_flags & MS_SYNCHRONOUS) ||
             (fi->flags & CEPH_F_SYNC)) {
+                mutex_unlock(&inode->i_mutex);
                 ret = ceph_sync_write(file, iov->iov_base, iov->iov_len,
                         &iocb->ki_pos);
         } else {
-                mutex_lock(&inode->i_mutex);
                 ret = __generic_file_aio_write(iocb, iov, nr_segs,
                                                &iocb->ki_pos);
                 mutex_unlock(&inode->i_mutex);
@@ -766,7 +767,6 @@ retry_snap:
                         __mark_inode_dirty(inode, dirty);
         }
 
-out_put:
         dout("aio_write %p %llx.%llx %llu~%u  dropping cap refs on %s\n",
              inode, ceph_vinop(inode), pos, (unsigned)iov->iov_len,
              ceph_cap_string(got));