Date: Wed, 19 Jun 2013 14:40:01 GMT From: "Steven Hartland" <smh@freebsd.org> To: freebsd-fs@FreeBSD.org Subject: Re: kern/161968: [zfs] [hang] renaming snapshot with -r including a zvol snapshot causes total ZFS freeze/lockup Message-ID: <201306191440.r5JEe1fN031062@freefall.freebsd.org>
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The following reply was made to PR kern/161968; it has been noted by GNATS.
From: "Steven Hartland" <smh@freebsd.org>
To: <bug-followup@freebsd.org>,
"Peter Maloney" <peter.maloney@brockmann-consult.de>
Cc:
Subject: Re: kern/161968: [zfs] [hang] renaming snapshot with -r including a zvol snapshot causes total ZFS freeze/lockup
Date: Wed, 19 Jun 2013 15:23:13 +0100
I've reproduced this here, the cause is a live lock between zvols geom
actions and ZFS itself between the two locks:
db> show sleepchain
thread 100553 (pid 6, txg_thread_enter) blocked on sx "spa_namespace_lock" XLOCK
thread 100054 (pid 2, g_event) blocked on sx "dp->dp_config_rwlock" XLOCK
db>
Tracing pid 2 tid 100054 td 0xffffff001c1d4470
sched_switch() at sched_switch+0x153
mi_switch() at mi_switch+0x1f8
sleepq_switch() at sleepq_switch+0x123
sleepq_wait() at sleepq_wait+0x4d
_sx_slock_hard() at _sx_slock_hard+0x1e2
_sx_slock() at _sx_slock+0xc9
dsl_dir_open_spa() at dsl_dir_open_spa+0xab
dsl_dataset_hold() at dsl_dataset_hold+0x3b
dsl_dataset_own() at dsl_dataset_own+0x2f
dmu_objset_own() at dmu_objset_own+0x36
zvol_first_open() at zvol_first_open+0x34
zvol_geom_access() at zvol_geom_access+0x2df
g_access() at g_access+0x1ba
g_part_taste() at g_part_taste+0xc4
g_new_provider_event() at g_new_provider_event+0xaa
g_run_events() at g_run_events+0x250
fork_exit() at fork_exit+0x135
fork_trampoline() at fork_trampoline+0xe
--- trap 0, rip = 0, rsp = 0xffffff92070a2bb0, rbp = 0 ---
db> bt 100553
Tracing pid 6 tid 100553 td 0xffffff002c2308e0
sched_switch() at sched_switch+0x153
mi_switch() at mi_switch+0x1f8
sleepq_switch() at sleepq_switch+0x123
sleepq_wait() at sleepq_wait+0x4d
_sx_xlock_hard() at _sx_xlock_hard+0x296
_sx_xlock() at _sx_xlock+0xb7
zvol_rename_minors() at zvol_rename_minors+0x75
dsl_dataset_snapshot_rename_sync() at dsl_dataset_snapshot_rename_sync+0x141
dsl_sync_task_group_sync() at dsl_sync_task_group_sync+0x14e
dsl_pool_sync() at dsl_pool_sync+0x47d
spa_sync() at spa_sync+0x34a
txg_sync_thread() at txg_sync_thread+0x139
fork_exit() at fork_exit+0x135
fork_trampoline() at fork_trampoline+0xe
--- trap 0, rip = 0, rsp = 0xffffff920e61abb0, rbp = 0 ---
The following steps recreate the issue on stable/8 r251496
gpart create -s GPT da3
gpart add -t freebsd-zfs da3
zpool create -f testpool da3p1
zfs create -V 150m testpool/testvol
zfs snapshot -r testpool@snap
zfs rename -r testpool@snap testpool@snap-new
I've been unable to reproduce on current r251471.
I'm not sure is this is due to a timing issue due to the significant
changes in ZFS sync tasks in current or if the issue really doesn't
exist any more.
Regards
Steve
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