cluster/dht : Do not migrate files with POSIX locks held

dht_migrate_file does not migrate file locks to the dst file.
Any locks held on the source file are lost once the migration
is complete. This issue is magnified in the case of a tier volume
as file migrations occur more frequently and repeatedly as compared
to a DHT rebalance.

The fix makes 2 changes:
1. Before starting the actual migration process, check if there are
 any locks held on the file. If yes, do not migrate the file.
2. The rebalance process tries to lock on the entire file just before
 moving into the Phase 2 of the file migration. If the lock acquisition
fails, the file migration does not proceed.
If the lock is granted, the file migration proceeds.

This still leaves a small window where conflicting locks can be granted to
different clients. If client1 requests a lock on the src file just after
it is converted to a linkto file and client2 requests a lock on the dst
data file, they will both be granted, but all FOPs will be redirected
to the dst data file. This issue will be taken up in a subsequent patch.

Change-Id: I8c895fc3cced50dd2894259d40a827c7b43d58ac
BUG: 1271148
Signed-off-by: N Balachandran <nbalacha@redhat.com>
Reviewed-on: http://review.gluster.org/12347
Tested-by: NetBSD Build System <jenkins@build.gluster.org>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Dan Lambright <dlambrig@redhat.com>
Tested-by: Dan Lambright <dlambrig@redhat.com>

1 files changed, 95 insertions, 10 deletions

diff --git a/xlators/cluster/dht/src/dht-rebalance.c b/xlators/cluster/dht/src/dht-rebalance.c
index a6c14b085fa..b3c25ba9ee2 100644
--- a/xlators/cluster/dht/src/dht-rebalance.c
+++ b/xlators/cluster/dht/src/dht-rebalance.c
@@ -389,6 +389,7 @@ __is_file_migratable (xlator_t *this, loc_t *loc,
                                 gf_defrag_info_t *defrag)
 {
         int ret = -1;
+        int lock_count = 0;
 
         if (IA_ISDIR (stbuf->ia_type)) {
                 gf_msg (this->name, GF_LOG_WARNING, 0,
@@ -399,10 +400,30 @@ __is_file_migratable (xlator_t *this, loc_t *loc,
                 goto out;
         }
 
+        ret = dict_get_int32 (xattrs, GLUSTERFS_POSIXLK_COUNT, &lock_count);
+        if (ret) {
+                gf_msg (this->name, GF_LOG_WARNING, 0,
+                        DHT_MSG_MIGRATE_FILE_FAILED,
+                        "Migrate file failed:"
+                        "%s: Unable to get lock count for file", loc->path);
+                ret = -1;
+                goto out;
+        }
+
+        if (lock_count) {
+                gf_msg (this->name, GF_LOG_WARNING, 0,
+                        DHT_MSG_MIGRATE_FILE_FAILED,
+                        "Migrate file failed: %s: File has locks."
+                        " Skipping file migration", loc->path);
+                ret = -1;
+                goto out;
+        }
+
         if (flags == GF_DHT_MIGRATE_HARDLINK_IN_PROGRESS) {
                 ret = 0;
                 goto out;
         }
+
         if (stbuf->ia_nlink > 1) {
                 /* support for decomission */
                 if (flags == GF_DHT_MIGRATE_HARDLINK) {
@@ -437,6 +458,7 @@ out:
         return ret;
 }
 
+
 static int
 __dht_rebalance_create_dst_file (xlator_t *to, xlator_t *from, loc_t *loc, struct iatt *stbuf,
                                  fd_t **dst_fd, dict_t *xattr)
@@ -993,7 +1015,6 @@ out:
         return ret;
 }
 
-
 static int
 __dht_migration_cleanup_src_file (xlator_t *this, loc_t *loc, fd_t *fd,
                                   xlator_t *from, ia_prot_t *src_ia_prot)
@@ -1084,11 +1105,14 @@ dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
         dht_conf_t     *conf                 = this->private;
         int             rcvd_enoent_from_src = 0;
         struct gf_flock flock                = {0, };
+        struct gf_flock plock                = {0, };
         loc_t           tmp_loc              = {0, };
         gf_boolean_t    locked               = _gf_false;
+        gf_boolean_t    p_locked             = _gf_false;
         int             lk_ret               = -1;
         gf_defrag_info_t *defrag             =  NULL;
         gf_boolean_t    clean_src            = _gf_false;
+        gf_boolean_t    clean_dst            = _gf_false;
 
         defrag = conf->defrag;
         if (!defrag)
@@ -1110,6 +1134,17 @@ dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
                 goto out;
         }
 
+
+        /* Don't migrate files with POSIX locks */
+        ret = dict_set_int32 (dict, GLUSTERFS_POSIXLK_COUNT, sizeof(int32_t));
+        if (ret) {
+                gf_msg (this->name, GF_LOG_ERROR, 0,
+                        DHT_MSG_MIGRATE_FILE_FAILED,
+                        "Migrate file failed: %s: failed to "
+                        "set "GLUSTERFS_POSIXLK_COUNT" key in dict", loc->path);
+                goto out;
+        }
+
         flock.l_type = F_WRLCK;
 
         tmp_loc.inode = inode_ref (loc->inode);
@@ -1162,6 +1197,7 @@ dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
                 goto out;
         }
 
+
         /* TODO: move all xattr related operations to fd based operations */
         ret = syncop_listxattr (from, loc, &xattr, NULL, NULL);
         if (ret < 0) {
@@ -1179,6 +1215,8 @@ dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
         if (ret)
                 goto out;
 
+        clean_dst = _gf_true;
+
         ret = __dht_check_free_space (to, from, loc, &stbuf, flag);
 
         if (ret) {
@@ -1211,6 +1249,7 @@ dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
         if (stbuf.ia_size > (stbuf.ia_blocks * GF_DISK_SECTOR_SIZE))
                 file_has_holes = 1;
 
+
         /* All I/O happens in this function */
         ret = __dht_rebalance_migrate_data (from, to, src_fd, dst_fd,
 					    stbuf.ia_size, file_has_holes);
@@ -1219,15 +1258,6 @@ dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
                         DHT_MSG_MIGRATE_FILE_FAILED,
                         "Migrate file failed: %s: failed to migrate data",
                         loc->path);
-                /* reset the destination back to 0 */
-                ret = syncop_ftruncate (to, dst_fd, 0, NULL, NULL);
-                if (ret) {
-                        gf_msg (this->name, GF_LOG_ERROR, 0,
-                                DHT_MSG_MIGRATE_FILE_FAILED,
-                                "Migrate file failed: "
-                                "%s: failed to reset target size back to 0 (%s)",
-                                loc->path, strerror (-ret));
-                }
 
                 ret = -1;
                 goto out;
@@ -1257,6 +1287,35 @@ dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
                 goto out;
         }
 
+        /* Lock the entire source file to prevent clients from taking a
+           lock on it as dht_lk does not handle file migration.
+
+           This still leaves a small window where conflicting locks can
+           be granted to different clients. If client1 requests a blocking
+           lock on the src file, it will be granted after the migrating
+           process releases its lock. If client2 requests a lock on the dst
+           data file, it will also be granted, but all FOPs will be redirected
+           to the dst data file.
+        */
+
+        plock.l_type = F_WRLCK;
+        plock.l_start = 0;
+        plock.l_len = 0;
+        plock.l_whence = SEEK_SET;
+
+        ret = syncop_lk (from, src_fd, F_SETLK, &plock, NULL, NULL);
+        if (ret) {
+                gf_msg (this->name, GF_LOG_ERROR, -ret,
+                        DHT_MSG_MIGRATE_FILE_FAILED,
+                        "Migrate file failed:"
+                        "%s: Failed to lock on %s",
+                        loc->path, from->name);
+                ret = -1;
+                goto out;
+        }
+
+        p_locked = _gf_true;
+
         /* source would have both sticky bit and sgid bit set, reset it to 0,
            and set the source permission on destination, if it was not set
            prior to setting rebalance-modes in source  */
@@ -1293,6 +1352,8 @@ dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
                 ret = -1;
         }
 
+        clean_dst = _gf_false;
+
         /* Posix acls are not set on DHT linkto files as part of the initial
          * initial xattrs set on the dst file, so these need
          * to be set on the dst file after the linkto attrs are removed.
@@ -1438,6 +1499,18 @@ out:
                 }
         }
 
+        /* reset the destination back to 0 */
+        if (clean_dst) {
+                ret = syncop_ftruncate (to, dst_fd, 0, NULL, NULL);
+                if (ret) {
+                        gf_msg (this->name, GF_LOG_ERROR, -ret,
+                                DHT_MSG_MIGRATE_FILE_FAILED,
+                                "Migrate file failed: "
+                                "%s: failed to reset target size back to 0",
+                                loc->path);
+                }
+        }
+
         if (locked) {
                 flock.l_type = F_UNLCK;
 
@@ -1451,6 +1524,18 @@ out:
                 }
         }
 
+        if (p_locked) {
+                plock.l_type = F_UNLCK;
+                lk_ret = syncop_lk (from, src_fd, F_SETLK, &plock, NULL, NULL);
+
+                if (lk_ret < 0) {
+                        gf_msg (this->name, GF_LOG_WARNING, -lk_ret,
+                                DHT_MSG_MIGRATE_FILE_FAILED,
+                                "%s: failed to unlock file on %s",
+                                loc->path, from->name);
+                }
+        }
+
         if (dict)
                 dict_unref (dict);