OpenZFS on Linux and FreeBSD
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loli10K 2a0d41889e Scrubbing root pools may deadlock on kernels without elevator_change() (#9321)
Originally the zfs_vdev_elevator module option was added as a
convenience so the requested elevator would be automatically set
on the underlying block devices. At the time this was simple
because the kernel provided an API function which did exactly this.

This API was then removed in the Linux 4.12 kernel which prompted
us to add compatibly code to set the elevator via a usermodehelper.

Unfortunately changing the evelator via usermodehelper requires reading
some userland binaries, most notably modprobe(8) or sh(1), from a zfs
dataset on systems with root-on-zfs. This can deadlock the system if
used during the following call path because it may need, if the data
is not already cached in the ARC, reading directly from disk while
holding the spa config lock as a writer:

  zfs_ioc_pool_scan()
    -> spa_scan()
      -> spa_scan()
        -> vdev_reopen()
          -> vdev_elevator_switch()
            -> call_usermodehelper()

While the usermodehelper waits sh(1), modprobe(8) is blocked in the
ZIO pipeline trying to read from disk:

  INFO: task modprobe:2650 blocked for more than 10 seconds.
       Tainted: P           OE     5.2.14
  modprobe        D    0  2650    206 0x00000000
  Call Trace:
   ? __schedule+0x244/0x5f0
   schedule+0x2f/0xa0
   cv_wait_common+0x156/0x290 [spl]
   ? do_wait_intr_irq+0xb0/0xb0
   spa_config_enter+0x13b/0x1e0 [zfs]
   zio_vdev_io_start+0x51d/0x590 [zfs]
   ? tsd_get_by_thread+0x3b/0x80 [spl]
   zio_nowait+0x142/0x2f0 [zfs]
   arc_read+0xb2d/0x19d0 [zfs]
   ...
   zpl_iter_read+0xfa/0x170 [zfs]
   new_sync_read+0x124/0x1b0
   vfs_read+0x91/0x140
   ksys_read+0x59/0xd0
   do_syscall_64+0x4f/0x130
   entry_SYSCALL_64_after_hwframe+0x44/0xa9

This commit changes how we use the usermodehelper functionality from
synchronous (UMH_WAIT_PROC) to asynchronous (UMH_NO_WAIT) which prevents
scrubs, and other vdev_elevator_switch() consumers, from triggering the
aforementioned issue.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Issue #8664 
Closes #9321
2019-09-13 18:09:59 -07:00
.github Fix typos 2019-09-02 18:17:39 -07:00
cmd Add subcommand to wait for background zfs activity to complete 2019-09-13 18:09:06 -07:00
config OpenZFS restructuring - move platform specific headers 2019-09-05 09:34:54 -07:00
contrib Fix typos in contrib/ 2019-08-30 09:44:43 -07:00
etc Fix typos in etc/ 2019-08-30 09:46:52 -07:00
include Add subcommand to wait for background zfs activity to complete 2019-09-13 18:09:06 -07:00
lib Add subcommand to wait for background zfs activity to complete 2019-09-13 18:09:06 -07:00
man Add subcommand to wait for background zfs activity to complete 2019-09-13 18:09:06 -07:00
module Scrubbing root pools may deadlock on kernels without elevator_change() (#9321) 2019-09-13 18:09:59 -07:00
rpm Canonicalize Python shebangs 2019-09-12 13:32:32 -07:00
scripts kmodtool: depmod path 2019-09-11 11:14:50 -07:00
tests Add subcommand to wait for background zfs activity to complete 2019-09-13 18:09:06 -07:00
udev Restore :: in Makefile.am 2019-08-26 11:48:31 -07:00
.gitignore Linux 5.3 compat: Makefile subdir-m no longer supported 2019-08-19 15:22:52 -07:00
.gitmodules Add zimport.sh compatibility test script 2014-02-21 12:10:31 -08:00
.travis.yml Add .travis.yml 2017-11-13 09:18:18 -08:00
AUTHORS Update build system and packaging 2018-05-29 16:00:33 -07:00
CODE_OF_CONDUCT.md Add CODE_OF_CONDUCT.md 2019-04-30 10:58:45 -07:00
COPYRIGHT OpenZFS restructuring - move platform specific sources 2019-09-06 11:26:26 -07:00
LICENSE Update build system and packaging 2018-05-29 16:00:33 -07:00
META Tag 0.8.0 2019-05-21 11:11:41 -07:00
Makefile.am OpenZFS restructuring - move platform specific sources 2019-09-06 11:26:26 -07:00
NEWS Add NEWS file 2018-09-18 12:03:47 -07:00
NOTICE Update build system and packaging 2018-05-29 16:00:33 -07:00
README.md Explicitly state supported Linux versions 2018-05-30 20:11:19 -07:00
TEST Update build system and packaging 2018-05-29 16:00:33 -07:00
autogen.sh Cause autogen.sh to fail if autoreconf fails 2018-07-06 09:27:37 -07:00
configure.ac Add subcommand to wait for background zfs activity to complete 2019-09-13 18:09:06 -07:00
copy-builtin copy-builtin: SPL must be in Kbuild first (again) 2019-09-11 11:09:50 -07:00
zfs.release.in Move zfs.release generation to configure step 2012-07-12 12:22:51 -07:00

README.md

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ZFS on Linux is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the OpenZFS community.

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Official Resources

Installation

Full documentation for installing ZoL on your favorite Linux distribution can be found at our site.

Contribute & Develop

We have a separate document with contribution guidelines.

Release

ZFS on Linux is released under a CDDL license.
For more details see the NOTICE, LICENSE and COPYRIGHT files; UCRL-CODE-235197

Supported Kernels

  • The META file contains the officially recognized supported kernel versions.