Zpool can start allocating from metaslab before TRIMs have completed #15395
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amotin
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behlendorf
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ikozhukhov
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@jasonbking can you force update this PR and add your |
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Status: Accepted
When doing a manual TRIM on a zpool, the metaslab being TRIMmed is potentially re-enabled before all queued TRIM zios for that metaslab have completed. Since TRIM zios have the lowest priority, it is possible to get into a situation where allocations occur from the just re-enabled metaslab and cut ahead of queued TRIMs to the same metaslab. If the ranges overlap, this will cause corruption. We were able to trigger this pretty consistently with a small single top-level vdev zpool (i.e. small number of metaslabs) with heavy parallel write activity while performing a manual TRIM against a somewhat 'slow' device (so TRIMs took a bit of time to complete). With the patch, we've not been able to recreate it since. It was on illumos, but inspection of the OpenZFS trim code looks like the relevant pieces are largely unchanged and so it appears it would be vulnerable to the same issue. The illumos bug for this is illumos#15939. Signed-off-by: Jason King <[email protected]>
behlendorf
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Oct 12, 2023
When doing a manual TRIM on a zpool, the metaslab being TRIMmed is potentially re-enabled before all queued TRIM zios for that metaslab have completed. Since TRIM zios have the lowest priority, it is possible to get into a situation where allocations occur from the just re-enabled metaslab and cut ahead of queued TRIMs to the same metaslab. If the ranges overlap, this will cause corruption. We were able to trigger this pretty consistently with a small single top-level vdev zpool (i.e. small number of metaslabs) with heavy parallel write activity while performing a manual TRIM against a somewhat 'slow' device (so TRIMs took a bit of time to complete). With the patch, we've not been able to recreate it since. It was on illumos, but inspection of the OpenZFS trim code looks like the relevant pieces are largely unchanged and so it appears it would be vulnerable to the same issue. Reviewed-by: Igor Kozhukhov <[email protected]> Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Brian Behlendorf <[email protected]> Signed-off-by: Jason King <[email protected]> Illumos-issue: https://www.illumos.org/issues/15939 Closes #15395
behlendorf
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When doing a manual TRIM on a zpool, the metaslab being TRIMmed is potentially re-enabled before all queued TRIM zios for that metaslab have completed. Since TRIM zios have the lowest priority, it is possible to get into a situation where allocations occur from the just re-enabled metaslab and cut ahead of queued TRIMs to the same metaslab. If the ranges overlap, this will cause corruption. We were able to trigger this pretty consistently with a small single top-level vdev zpool (i.e. small number of metaslabs) with heavy parallel write activity while performing a manual TRIM against a somewhat 'slow' device (so TRIMs took a bit of time to complete). With the patch, we've not been able to recreate it since. It was on illumos, but inspection of the OpenZFS trim code looks like the relevant pieces are largely unchanged and so it appears it would be vulnerable to the same issue. Reviewed-by: Igor Kozhukhov <[email protected]> Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Brian Behlendorf <[email protected]> Signed-off-by: Jason King <[email protected]> Illumos-issue: https://www.illumos.org/issues/15939 Closes openzfs#15395
defaziogiancarlo
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When doing a manual TRIM on a zpool, the metaslab being TRIMmed is potentially re-enabled before all queued TRIM zios for that metaslab have completed. Since TRIM zios have the lowest priority, it is possible to get into a situation where allocations occur from the just re-enabled metaslab and cut ahead of queued TRIMs to the same metaslab. If the ranges overlap, this will cause corruption. We were able to trigger this pretty consistently with a small single top-level vdev zpool (i.e. small number of metaslabs) with heavy parallel write activity while performing a manual TRIM against a somewhat 'slow' device (so TRIMs took a bit of time to complete). With the patch, we've not been able to recreate it since. It was on illumos, but inspection of the OpenZFS trim code looks like the relevant pieces are largely unchanged and so it appears it would be vulnerable to the same issue. Reviewed-by: Igor Kozhukhov <[email protected]> Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Brian Behlendorf <[email protected]> Signed-off-by: Jason King <[email protected]> Illumos-issue: https://www.illumos.org/issues/15939 Closes openzfs#15395
tonyhutter
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Nov 30, 2023
When doing a manual TRIM on a zpool, the metaslab being TRIMmed is potentially re-enabled before all queued TRIM zios for that metaslab have completed. Since TRIM zios have the lowest priority, it is possible to get into a situation where allocations occur from the just re-enabled metaslab and cut ahead of queued TRIMs to the same metaslab. If the ranges overlap, this will cause corruption. We were able to trigger this pretty consistently with a small single top-level vdev zpool (i.e. small number of metaslabs) with heavy parallel write activity while performing a manual TRIM against a somewhat 'slow' device (so TRIMs took a bit of time to complete). With the patch, we've not been able to recreate it since. It was on illumos, but inspection of the OpenZFS trim code looks like the relevant pieces are largely unchanged and so it appears it would be vulnerable to the same issue. Reviewed-by: Igor Kozhukhov <[email protected]> Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Brian Behlendorf <[email protected]> Signed-off-by: Jason King <[email protected]> Illumos-issue: https://www.illumos.org/issues/15939 Closes #15395
lundman
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Dec 12, 2023
When doing a manual TRIM on a zpool, the metaslab being TRIMmed is potentially re-enabled before all queued TRIM zios for that metaslab have completed. Since TRIM zios have the lowest priority, it is possible to get into a situation where allocations occur from the just re-enabled metaslab and cut ahead of queued TRIMs to the same metaslab. If the ranges overlap, this will cause corruption. We were able to trigger this pretty consistently with a small single top-level vdev zpool (i.e. small number of metaslabs) with heavy parallel write activity while performing a manual TRIM against a somewhat 'slow' device (so TRIMs took a bit of time to complete). With the patch, we've not been able to recreate it since. It was on illumos, but inspection of the OpenZFS trim code looks like the relevant pieces are largely unchanged and so it appears it would be vulnerable to the same issue. Reviewed-by: Igor Kozhukhov <[email protected]> Reviewed-by: Alexander Motin <[email protected]> Reviewed-by: Brian Behlendorf <[email protected]> Signed-off-by: Jason King <[email protected]> Illumos-issue: https://www.illumos.org/issues/15939 Closes openzfs#15395
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Wait for all TRIM zios for a metaslab to complete before re-enabling it.
Motivation and Context
During some load testing on a small, single disk zpool, we encountered consistent pool corruption with a combination of multiple parallel write workloads while running a manual TRIM (
zpool trim) on a pool.Description
When doing a manual TRIM on a zpool, the metaslab being TRIMmed is potentially re-enabled before all queued TRIM zios for that metaslab have completed. Since TRIM zios have the lowest priority, it is possible to get into a situation where allocations occur from the just re-enabled metaslab and cut ahead of queued TRIMs to the same metaslab. If the ranges overlap, this will cause corruption.
This was discovered on illumos (illumos#15939, however inspection of the OpenZFS codebase shows that the code in question is largely unchanged and appears vulnerable to the same corruption.
The fix is fairly simple. Once all the allocable (i.e. free) ranges for a metaslab have been issued, wait for them to complete before re-enabling the metaslab and moving onto the next metaslab to TRIM.
How Has This Been Tested?
Running the same workload (multiple write streams to a small, single disk zpool while running TRIM) that consistently (and quickly) produced corruption no longer caused corruption once the change had been applied.
Types of changes
Checklist:
Signed-off-by.