cluster/dht: Fix races to avoid deletion of linkto file

Explanation of Race between rebalance processes:
https://bugzilla.redhat.com/show_bug.cgi?id=1110694#c4

STATE 1:                          BRICK-1
only one brick                   Cached File
in the system

STATE 2:
Add brick-2                       BRICK-1                BRICK-2

STATE 3:                                       Lookup of File on brick-2
                                               by this node's rebalance
                                               will fail because hashed
                                               file is not created yet.
                                               So dht_lookup_everywhere is
                                               about to get called.

STATE 4:                         As part of lookup
                                 link file at brick-2
                                 will be created.

STATE 5:                         getxattr to check that
                                 cached file belongs to
                                 this node is done

STATE 6:

                                            dht_lookup_everywhere_cbk detects
                                            the link created by rebalance-1.
                                            It will unlink it.

STATE 7:                        getxattr at the link
                                file with "pathinfo" key
                                will be called will fail
                                as the link file is deleted
                                by rebalance on node-2

Fix:
So in the STATE 6, we should avoid the deletion of link file. Every time
dht_lookup_everywhere gets called, lookup will be performed on all the nodes.
So to avoid STATE 6, if linkto file is found, it is not deleted until valid
case is found in dht_lookup_everywhere_done.

Case 1: if linkto file points to cached node, and cached file exists,
        uwind with success.

Case 2: if linkto does not point to current cached node, and cached file
        exists:
        a) Unlink stale link file
        b) Create new link file

Case 3: Only linkto file exists:
        Delete linkto file

Case 4: Only cached file
        Create link file (Handled event without patch)

Case 5: Neither cached nor hashed file is present
        Return with ENOENT (handled even without patch)

Change-Id: Ibf53671410d8d613b8e2e7e5d0ec30fc7dcc0298
BUG: 1116150
Signed-off-by: Venkatesh Somyajulu <vsomyaju@redhat.com>
Reviewed-on: http://review.gluster.org/8231
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Tested-by: Vijay Bellur <vbellur@redhat.com>

1 files changed, 260 insertions, 27 deletions

diff --git a/xlators/cluster/dht/src/dht-common.c b/xlators/cluster/dht/src/dht-common.c
index 421f4917d86..c60fa56ffcf 100644
--- a/xlators/cluster/dht/src/dht-common.c
+++ b/xlators/cluster/dht/src/dht-common.c
@@ -850,6 +850,80 @@ out:
         return ret;
 }
 
+int
+dht_lookup_unlink_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
+                       int op_ret, int op_errno,
+                       struct iatt *preparent, struct iatt *postparent,
+                       dict_t *xdata)
+{
+        int  this_call_cnt = 0;
+
+        this_call_cnt = dht_frame_return (frame);
+        if (is_last_call (this_call_cnt)) {
+                dht_lookup_everywhere_done (frame, this);
+        }
+
+        return 0;
+}
+
+int
+dht_lookup_unlink_stale_linkto_cbk (call_frame_t *frame, void *cookie,
+                                    xlator_t *this, int op_ret, int op_errno,
+                                    struct iatt *preparent,
+                                    struct iatt *postparent, dict_t *xdata)
+{
+
+        /* NOTE:
+         * If stale file unlink fails either there is an open-fd or is not an
+         * dht-linkto-file then posix_unlink returns EBUSY, which is overwritten
+         *  to ENOENT
+         */
+
+        DHT_STACK_UNWIND (lookup, frame, -1, ENOENT, NULL, NULL, NULL,
+                          NULL);
+
+        return 0;
+}
+
+/* Rebalance is performed from cached_node to hashed_node. Initial cached_node
+ * contains a non-linkto file. After migration it is converted to linkto and
+ * then unlinked. And at hashed_subvolume, first a linkto file is present,
+ * then after migration it is converted to a non-linkto file.
+ *
+ * Lets assume a file is present on cached subvolume and a new brick is added
+ * and new brick is the new_hashed subvolume. So fresh lookup on newly added
+ * hashed subvolume will fail and dht_lookup_everywhere gets called.  If just
+ * before sending the dht_lookup_everywhere request rebalance is in progress,
+ *
+ * from cached subvolume it may see: Nonlinkto or linkto or No file
+ * from hashed subvolume it may see: No file or linkto file or non-linkto file
+ *
+ * So this boils down to 9 cases:
+ *   at cached_subvol            at hashed_subvol
+ *   ----------------           -----------------
+ *
+ *a)   No file                     No file
+ *    [request reached after    [Request reached before
+ *       migration]                Migration]
+ *
+ *b)   No file                     Linkto File
+ *
+ *c)   No file                     Non-Linkto File
+ *
+ *d)   Linkto                      No-File
+ *
+ *e)   Linkto                      Linkto
+ *
+ *f)   Linkto                      Non-Linkto
+ *
+ *g)   NonLinkto                   No-File
+ *
+ *h)   NonLinkto                   Linkto
+ *
+ *i)   NonLinkto                   NonLinkto
+ *
+ * dht_lookup_everywhere_done takes decision based on any of the above case
+ */
 
 int
 dht_lookup_everywhere_done (call_frame_t *frame, xlator_t *this)
@@ -860,6 +934,7 @@ dht_lookup_everywhere_done (call_frame_t *frame, xlator_t *this)
         xlator_t     *cached_subvol = NULL;
         dht_layout_t *layout = NULL;
         char gfid[GF_UUID_BUF_SIZE] = {0};
+        gf_boolean_t  found_non_linkto_on_hashed = _gf_false;
 
         local = frame->local;
         hashed_subvol = local->hashed_subvol;
@@ -884,19 +959,167 @@ dht_lookup_everywhere_done (call_frame_t *frame, xlator_t *this)
                 return 0;
         }
 
+
         if (!cached_subvol) {
-                DHT_STACK_UNWIND (lookup, frame, -1, ENOENT, NULL, NULL, NULL,
-                                  NULL);
+
+                if (local->skip_unlink.handle_valid_link && hashed_subvol) {
+
+                        /*Purpose of "unlink-only-if-dht-linkto-file":
+                         * If this lookup is performed by rebalance and this
+                         * rebalance process detected hashed file and by
+                         * the time it sends the lookup request to cached node,
+                         * file got migrated and now at intial hashed_node,
+                         * final migrated file is present. With current logic,
+                         * because this process fails to find the cached_node,
+                         * it will unlink the file at initial hashed_node.
+                         *
+                         * So we avoid this by setting key, and checking at the
+                         * posix_unlink that unlink the file only if file is a
+                         * linkto file and not a migrated_file.
+                         */
+
+                        ret = dict_set_int32 (local->xattr_req,
+                                              "unlink-only-if-dht-linkto-file",
+                                              1);
+
+                        if (ret)
+                                goto dict_err;
+
+                        /*Later other consumers can also use this key to avoid
+                         * unlinking in case of open_fd
+                         */
+
+                        ret = dict_set_int32 (local->xattr_req,
+                                              "dont-unlink-for-open-fd", 1);
+
+dict_err:
+                        if (ret) {
+                                /* If for some reason, setting key in the dict
+                                 * fails, return with ENOENT, as with respect to
+                                 * this process, it detected only a stale link
+                                 * file.
+                                 *
+                                 * Next lookup will delete it.
+                                 *
+                                 * Performing deletion of stale link file when
+                                 * setting key in dict fails, may cause the data
+                                 * loss becase of the above mentioned race.
+                                 */
+
+
+                                DHT_STACK_UNWIND (lookup, frame, -1, ENOENT,
+                                                  NULL, NULL, NULL, NULL);
+                        } else {
+                               local->skip_unlink.handle_valid_link = _gf_false;
+                                STACK_WIND (frame,
+                                            dht_lookup_unlink_stale_linkto_cbk,
+                                            hashed_subvol,
+                                            hashed_subvol->fops->unlink,
+                                            &local->loc, 0, local->xattr_req);
+                        }
+
+                } else  {
+
+                        DHT_STACK_UNWIND (lookup, frame, -1, ENOENT, NULL, NULL,
+                                          NULL, NULL);
+                }
                 return 0;
         }
 
-        if (local->need_lookup_everywhere) {
-                if (uuid_compare (local->gfid, local->inode->gfid)) {
-                        /* GFID different, return error */
-                        DHT_STACK_UNWIND (lookup, frame, -1, ENOENT, NULL,
-                                          NULL, NULL, NULL);
-                        return 0;
+        /* At the time of dht_lookup, no file was found on hashed and that is
+         * why dht_lookup_everywhere is called, but by the time
+         * dht_lookup_everywhere
+         * reached to server, file might have already migrated. In that case we
+         * will find a migrated file at the hashed_node. In this case store the
+         * layout in context and return successfully.
+         */
+
+        if (hashed_subvol || local->need_lookup_everywhere) {
+
+                if (local->need_lookup_everywhere) {
+
+                        found_non_linkto_on_hashed = _gf_true;
+
+                } else if ((local->file_count == 1) &&
+                            (hashed_subvol == cached_subvol)) {
+
+                        found_non_linkto_on_hashed = _gf_true;
+                }
+
+                if (found_non_linkto_on_hashed)
+                        goto preset_layout;
+
+        }
+
+
+        if (hashed_subvol) {
+                if (local->skip_unlink.handle_valid_link == _gf_true) {
+                        if (cached_subvol == local->skip_unlink.hash_links_to) {
+
+                             if (uuid_compare (local->skip_unlink.cached_gfid,
+                                               local->skip_unlink.hashed_gfid)){
+
+                                        /*GFID different, return error*/
+                                     DHT_STACK_UNWIND (lookup, frame, -1,
+                                                       ESTALE, NULL, NULL, NULL,
+                                                       NULL);
+
+
+                                }
+
+                                ret = dht_layout_preset (this, cached_subvol,
+                                                         local->loc.inode);
+                                if (ret) {
+                                        gf_log (this->name, GF_LOG_INFO,
+                                                "Could not set pre-set layout "
+                                                "for subvolume %s",
+                                                cached_subvol->name);
+                                }
+
+                                local->op_ret = (ret == 0) ? ret : -1;
+                                local->op_errno = (ret == 0) ? ret : EINVAL;
+
+                                /* Presence of local->cached_subvol validates
+                                 * that lookup from cached node is successful
+                                 */
+
+                                if (!local->op_ret && local->loc.parent) {
+                                        dht_inode_ctx_time_update
+                                                (local->loc.parent, this,
+                                                 &local->postparent, 1);
+                                }
+                                goto unwind_hashed_and_cached;
+                        } else {
+
+                               local->skip_unlink.handle_valid_link = _gf_false;
+                                if (local->skip_unlink.opend_fd_count == 0) {
+                                        local->call_cnt = 1;
+                                        STACK_WIND (frame, dht_lookup_unlink_cbk,
+                                                    hashed_subvol,
+                                                    hashed_subvol->fops->unlink,
+                                                    &local->loc, 0, NULL);
+                                        return 0;
+
+                                }
+                        }
+
                 }
+        }
+
+
+preset_layout:
+
+        if (found_non_linkto_on_hashed) {
+
+                if (local->need_lookup_everywhere) {
+                        if (uuid_compare (local->gfid, local->inode->gfid)) {
+                                /* GFID different, return error */
+                                DHT_STACK_UNWIND (lookup, frame, -1, ENOENT,
+                                                  NULL, NULL, NULL, NULL);
+                                return 0;
+                        }
+                }
+
                 local->op_ret = 0;
                 local->op_errno = 0;
                 layout = dht_layout_for_subvol (this, cached_subvol);
@@ -977,26 +1200,15 @@ dht_lookup_everywhere_done (call_frame_t *frame, xlator_t *this)
                                    cached_subvol, hashed_subvol, &local->loc);
 
         return ret;
-}
-
-
-int
-dht_lookup_unlink_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
-                       int op_ret, int op_errno,
-                       struct iatt *preparent, struct iatt *postparent,
-                       dict_t *xdata)
-{
-        int  this_call_cnt = 0;
-
-        this_call_cnt = dht_frame_return (frame);
-        if (is_last_call (this_call_cnt)) {
-                dht_lookup_everywhere_done (frame, this);
-        }
 
+unwind_hashed_and_cached:
+        DHT_STRIP_PHASE1_FLAGS (&local->stbuf);
+        DHT_STACK_UNWIND (lookup, frame, local->op_ret, local->op_errno,
+                          local->loc.inode, &local->stbuf, local->xattr,
+                          &local->postparent);
         return 0;
 }
 
-
 int
 dht_lookup_everywhere_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                            int32_t op_ret, int32_t op_errno,
@@ -1089,6 +1301,9 @@ dht_lookup_everywhere_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
 
                                 dht_iatt_merge (this, &local->postparent,
                                                 postparent, subvol);
+
+                                uuid_copy (local->skip_unlink.cached_gfid,
+                                           buf->ia_gfid);
                         } else {
                                 /* This is where we need 'rename' both entries logic */
                                 gf_msg (this->name, GF_LOG_WARNING, 0,
@@ -1106,9 +1321,27 @@ unlock:
 
         if (is_linkfile) {
                 ret = dict_get_int32 (xattr, GLUSTERFS_OPEN_FD_COUNT, &fd_count);
-                /* Delete the linkfile only if there are no open fds on it.
-                   if there is a open-fd, it may be in migration */
-                if (!ret && (fd_count == 0)) {
+
+                /*  Any linkto file found on the non-hashed subvolume should
+                 *  be unlinked (performed in the "else if" block below)
+                 *
+                 *  But if a linkto file is found on hashed subvolume, it may be
+                 *  pointing to vaild cached node. So unlinking of linkto
+                 *  file on hashed subvolume is skipped and inside
+                 *  dht_lookup_everywhere_done, checks are performed. If this
+                 *  linkto file is found as stale linkto file, it is deleted
+                 *  otherwise unlink is skipped.
+                 */
+
+                if (local->hashed_subvol && local->hashed_subvol == subvol) {
+
+                        local->skip_unlink.handle_valid_link = _gf_true;
+                        local->skip_unlink.opend_fd_count = fd_count;
+                        local->skip_unlink.hash_links_to = link_subvol;
+                        uuid_copy (local->skip_unlink.hashed_gfid,
+                                   buf->ia_gfid);
+
+                } else if (!ret && (fd_count == 0)) {
                         gf_log (this->name, GF_LOG_INFO,
                                 "deleting stale linkfile %s on %s",
                                 loc->path, subvol->name);