features/shard: Fix EIO error on add-brick

        Backport of: https://review.gluster.org/14419

DHT seems to link inode during lookup even before initializing
inode ctx with layout information, which comes after
directory healing.

Consider two parallel writes. As part of the first write,
shard sends lookup on .shard which in its return path would
cause DHT to link .shard inode. Now at this point, when a
second write is wound, inode_find() of .shard succeeds and
as a result of this, shard goes to create the participant
shards by issuing MKNODs under .shard. Since the layout is
yet to be initialized, mknod fails in dht call path with EIO,
leading to VM pauses.

The fix involves shard maintaining a flag to denote whether
a fresh lookup on .shard completed one network trip. If it
didn't, all inode_find()s in fop path will be followed by a
lookup before proceeding with the next stage of the fop.

Big thanks to Raghavendra G and Pranith Kumar K for the RCA
and subsequent inputs and feedback on the patch.

Change-Id: I66a7adf177e338a7691f441f199dde7c2b90c292
BUG: 1387878
Signed-off-by: Krutika Dhananjay <kdhananj@redhat.com>
Reviewed-on: https://review.gluster.org/16750
Smoke: Gluster Build System <jenkins@build.gluster.org>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
Reviewed-by: Pranith Kumar Karampuri <pkarampu@redhat.com>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Niels de Vos <ndevos@redhat.com>

2 files changed, 154 insertions, 19 deletions

diff --git a/xlators/features/shard/src/shard.c b/xlators/features/shard/src/shard.c
index 59a0cfa53cf..39d648bb34d 100644
--- a/xlators/features/shard/src/shard.c
+++ b/xlators/features/shard/src/shard.c
@@ -178,6 +178,63 @@ shard_inode_ctx_set (inode_t *inode, xlator_t *this, struct iatt *stbuf,
 }
 
 int
+__shard_inode_ctx_set_refreshed_flag (inode_t *inode, xlator_t *this)
+{
+        int                 ret = -1;
+        shard_inode_ctx_t  *ctx = NULL;
+
+        ret = __shard_inode_ctx_get (inode, this, &ctx);
+        if (ret)
+                return ret;
+
+        ctx->refreshed = _gf_true;
+        return 0;
+}
+
+int
+shard_inode_ctx_set_refreshed_flag (inode_t *inode, xlator_t *this)
+{
+        int ret = -1;
+
+        LOCK (&inode->lock);
+        {
+                ret = __shard_inode_ctx_set_refreshed_flag (inode, this);
+        }
+        UNLOCK (&inode->lock);
+
+        return ret;
+}
+
+gf_boolean_t
+__shard_inode_ctx_needs_lookup (inode_t *inode, xlator_t *this)
+{
+        int                 ret = -1;
+        shard_inode_ctx_t  *ctx = NULL;
+
+        ret = __shard_inode_ctx_get (inode, this, &ctx);
+        /* If inode ctx get fails, better to err on the side of caution and
+         * try again? Unless the failure is due to mem-allocation.
+         */
+        if (ret)
+                return _gf_true;
+
+        return !ctx->refreshed;
+}
+
+gf_boolean_t
+shard_inode_ctx_needs_lookup (inode_t *inode, xlator_t *this)
+{
+        gf_boolean_t flag = _gf_false;
+
+        LOCK (&inode->lock);
+        {
+                flag = __shard_inode_ctx_needs_lookup (inode, this);
+        }
+        UNLOCK (&inode->lock);
+
+        return flag;
+}
+int
 __shard_inode_ctx_invalidate (inode_t *inode, xlator_t *this, struct iatt *stbuf)
 {
         int                 ret = -1;
@@ -756,7 +813,7 @@ out:
 
 }
 
-static void
+static inode_t *
 shard_link_dot_shard_inode (shard_local_t *local, inode_t *inode,
                             struct iatt *buf)
 {
@@ -765,10 +822,72 @@ shard_link_dot_shard_inode (shard_local_t *local, inode_t *inode,
 
         priv = THIS->private;
 
-        linked_inode = inode_link (inode, local->dot_shard_loc.parent,
-                                   local->dot_shard_loc.name, buf);
+        linked_inode = inode_link (inode, inode->table->root, ".shard", buf);
         inode_lookup (linked_inode);
         priv->dot_shard_inode = linked_inode;
+        return linked_inode;
+}
+
+
+int
+shard_refresh_dot_shard_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
+                             int32_t op_ret, int32_t op_errno, inode_t *inode,
+                             struct iatt *buf, dict_t *xdata,
+                             struct iatt *postparent)
+{
+        shard_local_t *local = NULL;
+
+        local = frame->local;
+
+        if (op_ret) {
+                local->op_ret = op_ret;
+                local->op_errno = op_errno;
+                goto out;
+        }
+
+        /* To-Do: Fix refcount increment per call to
+         * shard_link_dot_shard_inode().
+         */
+        shard_link_dot_shard_inode (local, inode, buf);
+        shard_inode_ctx_set_refreshed_flag (inode, this);
+out:
+        shard_common_resolve_shards (frame, this, local->post_res_handler);
+        return 0;
+}
+
+int
+shard_refresh_dot_shard (call_frame_t *frame, xlator_t *this)
+{
+        loc_t          loc       = {0,};
+        inode_t       *inode     = NULL;
+        shard_priv_t  *priv      = NULL;
+        shard_local_t *local     = NULL;
+
+        local = frame->local;
+        priv = this->private;
+
+        inode = inode_find (this->itable, priv->dot_shard_gfid);
+
+        if (!shard_inode_ctx_needs_lookup (inode, this)) {
+                local->op_ret = 0;
+                goto out;
+        }
+
+        /* Plain assignment because the ref is already taken above through
+         * call to inode_find()
+         */
+        loc.inode = inode;
+        gf_uuid_copy (loc.gfid, priv->dot_shard_gfid);
+
+        STACK_WIND (frame, shard_refresh_dot_shard_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->lookup, &loc, NULL);
+        loc_wipe (&loc);
+
+        return 0;
+
+out:
+        shard_common_resolve_shards (frame, this, local->post_res_handler);
+        return 0;
 }
 
 int
@@ -777,7 +896,8 @@ shard_lookup_dot_shard_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                             struct iatt *buf, dict_t *xdata,
                             struct iatt *postparent)
 {
-        shard_local_t *local = NULL;
+        inode_t       *link_inode = NULL;
+        shard_local_t *local      = NULL;
 
         local = frame->local;
 
@@ -797,8 +917,14 @@ shard_lookup_dot_shard_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                 goto unwind;
         }
 
-        shard_link_dot_shard_inode (local, inode, buf);
-        shard_common_resolve_shards (frame, this, local->post_res_handler);
+        link_inode = shard_link_dot_shard_inode (local, inode, buf);
+        if (link_inode != inode) {
+                shard_refresh_dot_shard (frame, this);
+        } else {
+                shard_inode_ctx_set_refreshed_flag (link_inode, this);
+                shard_common_resolve_shards (frame, this,
+                                             local->post_res_handler);
+        }
         return 0;
 
 unwind:
@@ -1843,8 +1969,8 @@ shard_truncate_begin (call_frame_t *frame, xlator_t *this)
                 shard_lookup_dot_shard (frame, this,
                                         shard_post_resolve_truncate_handler);
         } else {
-                shard_common_resolve_shards (frame, this,
-                                           shard_post_resolve_truncate_handler);
+                local->post_res_handler = shard_post_resolve_truncate_handler;
+                shard_refresh_dot_shard (frame, this);
         }
         return 0;
 
@@ -2273,8 +2399,8 @@ shard_unlink_base_file_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                 shard_lookup_dot_shard (frame, this,
                                         shard_post_resolve_unlink_handler);
         } else {
-                shard_common_resolve_shards (frame, this,
-                                             shard_post_resolve_unlink_handler);
+                local->post_res_handler = shard_post_resolve_unlink_handler;
+                shard_refresh_dot_shard (frame, this);
         }
 
         return 0;
@@ -2624,8 +2750,8 @@ shard_rename_unlink_dst_shards_do (call_frame_t *frame, xlator_t *this)
                 shard_lookup_dot_shard (frame, this,
                                         shard_post_resolve_unlink_handler);
         } else {
-                shard_common_resolve_shards (frame, this,
-                                             shard_post_resolve_unlink_handler);
+                local->post_res_handler = shard_post_resolve_unlink_handler;
+                shard_refresh_dot_shard (frame, this);
         }
 
         return 0;
@@ -3388,8 +3514,8 @@ shard_post_lookup_readv_handler (call_frame_t *frame, xlator_t *this)
                 shard_lookup_dot_shard (frame, this,
                                         shard_post_resolve_readv_handler);
         } else {
-                shard_common_resolve_shards (frame, this,
-                                             shard_post_resolve_readv_handler);
+                local->post_res_handler = shard_post_resolve_readv_handler;
+                shard_refresh_dot_shard (frame, this);
         }
         return 0;
 
@@ -3849,7 +3975,8 @@ shard_mkdir_dot_shard_cbk (call_frame_t *frame, void *cookie,
                                        struct iatt *buf, struct iatt *preparent,
                                        struct iatt *postparent, dict_t *xdata)
 {
-        shard_local_t *local = NULL;
+        inode_t       *link_inode = NULL;
+        shard_local_t *local      = NULL;
 
         local = frame->local;
 
@@ -3869,8 +3996,15 @@ shard_mkdir_dot_shard_cbk (call_frame_t *frame, void *cookie,
                 }
         }
 
-        shard_link_dot_shard_inode (local, inode, buf);
-
+        link_inode = shard_link_dot_shard_inode (local, inode, buf);
+        if (link_inode != inode) {
+                shard_refresh_dot_shard (frame, this);
+        } else {
+                shard_inode_ctx_set_refreshed_flag (link_inode, this);
+                shard_common_resolve_shards (frame, this,
+                                             local->post_res_handler);
+        }
+        return 0;
 unwind:
         shard_common_resolve_shards (frame, this, local->post_res_handler);
         return 0;
@@ -4638,8 +4772,8 @@ shard_common_inode_write_begin (call_frame_t *frame, xlator_t *this,
                 shard_mkdir_dot_shard (frame, this,
                                  shard_common_inode_write_post_resolve_handler);
         } else {
-                shard_common_resolve_shards (frame, this,
-                                 shard_common_inode_write_post_resolve_handler);
+                local->post_res_handler = shard_common_inode_write_post_resolve_handler;
+                shard_refresh_dot_shard (frame, this);
         }
 
         return 0;
diff --git a/xlators/features/shard/src/shard.h b/xlators/features/shard/src/shard.h
index f626fae33c1..09232a45f24 100644
--- a/xlators/features/shard/src/shard.h
+++ b/xlators/features/shard/src/shard.h
@@ -268,6 +268,7 @@ typedef struct shard_inode_ctx {
         struct list_head ilist;
         uuid_t base_gfid;
         int block_num;
+        gf_boolean_t refreshed;
 } shard_inode_ctx_t;
 
 #endif /* __SHARD_H__ */