UBUNTU: SAUCE: (noup) zfs to 0.7.5-1ubuntu16.3

BugLink: http://bugs.launchpad.net/bugs/1781364
This is a sync of zfs 0.7.5-1ubuntu16.3 that fixes a mount/umount deadlock
for upstream ZFS commit ac09630d8b0b ("Fix zpl_mount() deadlock")

ZFS commit 93b43af inadvertently introduced the following scenario which
can result in a deadlock.  This issue was most easily reproduced by
LXD containers using a ZFS storage backend but should be reproducible
under any workload which is frequently mounting and unmounting.

-- THREAD A --
spa_sync()
  spa_sync_upgrades()
    rrw_enter(&dp->dp_config_rwlock, RW_WRITER, FTAG); <- Waiting on B

-- THREAD B --
mount_fs()
  zpl_mount()
    zpl_mount_impl()
      dmu_objset_hold()
        dmu_objset_hold_flags()
          dsl_pool_hold()
            dsl_pool_config_enter()
              rrw_enter(&dp->dp_config_rwlock, RW_READER, tag);
    sget()
      sget_userns()
        grab_super()
          down_write(&s->s_umount); <- Waiting on C

-- THREAD C --
cleanup_mnt()
  deactivate_super()
    down_write(&s->s_umount);
    deactivate_locked_super()
      zpl_kill_sb()
        kill_anon_super()
          generic_shutdown_super()
            sync_filesystem()
              zpl_sync_fs()
                zfs_sync()
                  zil_commit()
                    txg_wait_synced() <- Waiting on A

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
(backport from ZFS upstream commit ac09630d8b0bf6c92084a30fdaefd03fd0adbdc1)
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/zfs/META b/zfs/META
index 2110eef1b19d6d0902f7ca52422ff06bd0cd444f..a906a795ccd50499d861a02e154ee746ab4d0359 100644 (file)
--- a/zfs/META
+++ b/zfs/META
@@ -2,7 +2,7 @@ Meta:         1
 Name:         zfs
 Branch:       1.0
 Version:      0.7.5
-Release:      1ubuntu15
+Release:      1ubuntu16.3
 Release-Tags: relext
 License:      CDDL
 Author:       OpenZFS on Linux

diff --git a/zfs/include/sys/zfs_vfsops.h b/zfs/include/sys/zfs_vfsops.h
index 2326da42218315629b9e7caeca08a9c1af70515b..927153b25af96c44bd1007deb00c426111c78277 100644 (file)
--- a/zfs/include/sys/zfs_vfsops.h
+++ b/zfs/include/sys/zfs_vfsops.h
@@ -32,6 +32,7 @@
 #include <sys/zil.h>
 #include <sys/sa.h>
 #include <sys/rrwlock.h>
+#include <sys/dsl_dataset.h>
 #include <sys/zfs_ioctl.h>
 
 #ifdef __cplusplus

diff --git a/zfs/module/zfs/zpl_super.c b/zfs/module/zfs/zpl_super.c
index 848bb3c1062796ed09ea36b565e5ad23af14fae4..6292e2c2e2df4ef69dba4a759281a2c8b5507134 100644 (file)
--- a/zfs/module/zfs/zpl_super.c
+++ b/zfs/module/zfs/zpl_super.c
@@ -271,8 +271,17 @@ zpl_mount_impl(struct file_system_type *fs_type, int flags, zfs_mnt_t *zm)
        if (err)
                return (ERR_PTR(-err));
 
+       /*
+        * The dsl pool lock must be released prior to calling sget().
+        * It is possible sget() may block on the lock in grab_super()
+        * while deactivate_super() holds that same lock and waits for
+        * a txg sync.  If the dsl_pool lock is held over over sget()
+        * this can prevent the pool sync and cause a deadlock.
+        */
+       dsl_pool_rele(dmu_objset_pool(os), FTAG);
        s = zpl_sget(fs_type, zpl_test_super, set_anon_super, flags, os);
-       dmu_objset_rele(os, FTAG);
+       dsl_dataset_rele(dmu_objset_ds(os), FTAG);
+
        if (IS_ERR(s))
                return (ERR_CAST(s));