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Scrubbing root pools may deadlock on kernels without elevator_change() #9321
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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>
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Sep 13, 2019
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@@ Coverage Diff @@
## master #9321 +/- ##
==========================================
- Coverage 79.09% 79.07% -0.02%
==========================================
Files 401 401
Lines 122089 122074 -15
==========================================
- Hits 96568 96532 -36
- Misses 25521 25542 +21
Continue to review full report at Codecov.
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tonyhutter
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Sep 17, 2019
openzfs#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 openzfs#8664 Closes openzfs#9321
tonyhutter
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to tonyhutter/zfs
that referenced
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Sep 18, 2019
openzfs#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 openzfs#8664 Closes openzfs#9321
tonyhutter
pushed a commit
to tonyhutter/zfs
that referenced
this pull request
Sep 18, 2019
openzfs#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 openzfs#8664 Closes openzfs#9321
tonyhutter
pushed a commit
to tonyhutter/zfs
that referenced
this pull request
Sep 18, 2019
openzfs#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 openzfs#8664 Closes openzfs#9321
tonyhutter
pushed a commit
to tonyhutter/zfs
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Sep 19, 2019
openzfs#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 openzfs#8664 Closes openzfs#9321
tonyhutter
pushed a commit
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that referenced
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Sep 23, 2019
openzfs#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 openzfs#8664 Closes openzfs#9321
tonyhutter
pushed a commit
that referenced
this pull request
Sep 26, 2019
#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
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Motivation and Context
Fix #8664
This fix is an alternative to #9317 and will be hopefully easier to backport to the 0.8 release branch.
Description
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)
orsh(1)
, from a zfsdataset 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:
While the usermodehelper waits
sh(1)
,modprobe(8)
is blocked in the ZIO pipeline trying to read from disk:This commit changes how we use the usermodehelper functionality from
synchronous (
UMH_WAIT_PROC
) to asynchronous (UMH_NO_WAIT
) which preventsscrubs, and other
vdev_elevator_switch()
consumers, from triggering theaforementioned issue.
How Has This Been Tested?
Tested on local Debian builder with root pool (mirror) with
primarycache=none
runningzpool scrub -s
/zpool scrub -s rpool
in a loop.Types of changes
Checklist:
Signed-off-by
.