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When doing a device removal on a pool with gang blocks, the zio pipeline
can deadlock when trying to free blocks from a device which is being
removed with a stack similar to this:
0xffff8ab9a13a1740 UNINTERRUPTIBLE 4
__schedule+0x2e5
__schedule+0x2e5
schedule+0x33
schedule_preempt_disabled+0xe
__mutex_lock.isra.12+0x2a7
__mutex_lock.isra.12+0x2a7
__mutex_lock_slowpath+0x13
mutex_lock+0x2c
free_from_removing_vdev+0x61
metaslab_free_impl+0xd6
metaslab_free_dva+0x5e
metaslab_free+0x196
zio_free_sync+0xe4
zio_free_gang+0x38
zio_gang_tree_issue+0x42
zio_gang_tree_issue+0xa2
zio_gang_issue+0x6d
zio_execute+0x94
zio_execute+0x94
taskq_thread+0x23b
kthread+0x120
ret_from_fork+0x1f
Since there are gang blocks we have to read the gang members as part of
the free. This can be seen with a zio dependency tree that looks like
this:
sdb> echo 0xffff900c24f8a700 | zio -rc | zio
ADDRESS TYPE STAGE WAITER
0xffff900c24f8a700 NULL CHECKSUM_VERIFY 0xffff900ddfd31740
0xffff900c24f8c920 FREE GANG_ASSEMBLE -
0xffff900d93d435a0 READ DONE
In the illustration above we are processing frees but because of gang
block we have to read the constituents blocks. Once we finish the READ
in the zio pipeline we will execute the parent. In this case the parent
is a FREE but the zio taskq is a READ and we continue to process the
pipeline leading to the stack above. In the stack above, we are blocked
waiting for the svr_lock so as a result a READ interrupt taskq thread
is now consumed. Eventually, all of the READ taskq threads end up
blocked and we're unable to complete any read requests.
In zio_notify_parent there is an optimization to continue to use
the taskq thread to exectue the parent's pipeline. To resolve the
deadlock above, we only allow this optimization if the parent's
zio type matches the child which just completed.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Signed-off-by: George Wilson <gwilson@delphix.com>
External-issue: DLPX-80130
Closes #14236
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OpenZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the OpenZFS community. This repository contains the code for running OpenZFS on Linux and FreeBSD.
Official Resources
- Documentation - for using and developing this repo
- ZoL Site - Linux release info & links
- Mailing lists
- OpenZFS site - for conference videos and info on other platforms (illumos, OSX, Windows, etc)
Installation
Full documentation for installing OpenZFS on your favorite operating system can be found at the Getting Started Page.
Contribute & Develop
We have a separate document with contribution guidelines.
We have a Code of Conduct.
Release
OpenZFS is released under a CDDL license.
For more details see the NOTICE, LICENSE and COPYRIGHT files; UCRL-CODE-235197
Supported Kernels
- The
METAfile contains the officially recognized supported Linux kernel versions. - Supported FreeBSD versions are any supported branches and releases starting from 12.2-RELEASE.