diff options
| author | Brian Behlendorf <[email protected]> | 2018-07-11 15:49:10 -0700 |
|---|---|---|
| committer | GitHub <[email protected]> | 2018-07-11 15:49:10 -0700 |
| commit | ac09630d8b0bf6c92084a30fdaefd03fd0adbdc1 (patch) | |
| tree | 8133747cd7b694825e210f240dbe67f927360f33 | |
| parent | 33a19e0fd9b22364d295351ea1bda57b80e39e85 (diff) | |
Fix zpl_mount() deadlock
Commit 93b43af10 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
Reviewed by: Alek Pinchuk <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #7598
Closes #7659
Closes #7691
Closes #7693
| -rw-r--r-- | include/sys/zfs_vfsops.h | 1 | ||||
| -rw-r--r-- | module/zfs/zpl_super.c | 11 |
2 files changed, 11 insertions, 1 deletions
diff --git a/include/sys/zfs_vfsops.h b/include/sys/zfs_vfsops.h index febfdff97..31c9c6d7f 100644 --- a/include/sys/zfs_vfsops.h +++ b/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/module/zfs/zpl_super.c b/module/zfs/zpl_super.c index fc10271b7..5c426b0a9 100644 --- a/module/zfs/zpl_super.c +++ b/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)); |