1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
2 From: Rohan Puri <rohan.puri15@gmail.com>
3 Date: Sat, 28 Jul 2018 18:32:12 +0530
4 Subject: [PATCH] Fix deadlock between zfs umount & snapentry_expire
6 zfs umount -> zfsctl_destroy() takes the zfs_snapshot_lock as a
7 writer and calls zfsctl_snapshot_unmount_cancel(), which waits
8 for snapentry_expire() if present (when snap is automounted).
9 This snapentry_expire() itself then waits for zfs_snapshot_lock
10 as a reader, resulting in a deadlock.
12 The fix is to only hold the zfs_snapshot_lock over the tree
13 lookup and removal. After a successful lookup the lock can
14 be dropped and zfs_snapentry_t will remain valid until the
15 reference taken by the lookup is released.
17 Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
18 Signed-off-by: Rohan Puri <rohan.puri15@gmail.com>
22 (Cherry-picked from fd7265c646f40e364396af5014bbb83e809e124a)
23 Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
25 Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
27 module/zfs/zfs_ctldir.c | 11 +++++------
28 1 file changed, 5 insertions(+), 6 deletions(-)
30 diff --git a/module/zfs/zfs_ctldir.c b/module/zfs/zfs_ctldir.c
31 index 98897fe6..0ab5b4f0 100644
32 --- a/module/zfs/zfs_ctldir.c
33 +++ b/module/zfs/zfs_ctldir.c
34 @@ -358,8 +358,6 @@ snapentry_expire(void *data)
36 zfsctl_snapshot_unmount_cancel(zfs_snapentry_t *se)
38 - ASSERT(RW_LOCK_HELD(&zfs_snapshot_lock));
40 if (taskq_cancel_id(system_delay_taskq, se->se_taskqid) == 0) {
41 se->se_taskqid = TASKQID_INVALID;
42 zfsctl_snapshot_rele(se);
43 @@ -570,13 +568,14 @@ zfsctl_destroy(zfsvfs_t *zfsvfs)
44 uint64_t objsetid = dmu_objset_id(zfsvfs->z_os);
46 rw_enter(&zfs_snapshot_lock, RW_WRITER);
47 - if ((se = zfsctl_snapshot_find_by_objsetid(spa, objsetid))
49 - zfsctl_snapshot_unmount_cancel(se);
50 + se = zfsctl_snapshot_find_by_objsetid(spa, objsetid);
52 zfsctl_snapshot_remove(se);
53 + rw_exit(&zfs_snapshot_lock);
55 + zfsctl_snapshot_unmount_cancel(se);
56 zfsctl_snapshot_rele(se);
58 - rw_exit(&zfs_snapshot_lock);
59 } else if (zfsvfs->z_ctldir) {
60 iput(zfsvfs->z_ctldir);
61 zfsvfs->z_ctldir = NULL;