Fix deadlock on dmu_tx_assign() from vdev_rebuild()#18258
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behlendorf merged 1 commit intoopenzfs:masterfrom Feb 26, 2026
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Fix deadlock on dmu_tx_assign() from vdev_rebuild()#18258behlendorf merged 1 commit intoopenzfs:masterfrom
behlendorf merged 1 commit intoopenzfs:masterfrom
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Status: Accepted
vdev_rebuild() is always called with spa_config_lock held in
RW_WRITER mode. However, when it tries to call dmu_tx_assign()
the latter may hang on dmu_tx_wait() waiting for available txg.
But that available txg may not happen because txg_sync takes
spa_config_lock in order to process the current txg. So we have
a deadlock case here:
- dmu_tx_assign() waits for txg holding spa_config_lock;
- txg_sync waits for spa_config_lock not progressing with txg.
Here are the stacks:
__schedule+0x24e/0x590
schedule+0x69/0x110
cv_wait_common+0xf8/0x130 [spl]
__cv_wait+0x15/0x20 [spl]
dmu_tx_wait+0x8e/0x1e0 [zfs]
dmu_tx_assign+0x49/0x80 [zfs]
vdev_rebuild_initiate+0x39/0xc0 [zfs]
vdev_rebuild+0x84/0x90 [zfs]
spa_vdev_attach+0x305/0x680 [zfs]
zfs_ioc_vdev_attach+0xc7/0xe0 [zfs]
cv_wait_common+0xf8/0x130 [spl]
__cv_wait+0x15/0x20 [spl]
spa_config_enter+0xf9/0x120 [zfs]
spa_sync+0x6d/0x5b0 [zfs]
txg_sync_thread+0x266/0x2f0 [zfs]
The solution is to pass txg returned by spa_vdev_enter(spa)
at the top of spa_vdev_attach() to vdev_rebuild() and call
dmu_tx_create_assigned(txg) which doesn't wait for txg.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Andriy Tkachuk <andriy.tkachuk@seagate.com>
Closes openzfs#18210.
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I've just rebased it on the latest master. |
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Motivation and Context
Deadlock on spa_vdev_attach(), see #18210.
Description
vdev_rebuild() is always called with spa_config_lock held in RW_WRITER mode. However, when it tries to call dmu_tx_assign() the latter may hang on dmu_tx_wait() waiting for available txg. But that available txg may not happen because txg_sync takes spa_config_lock in order to process the current txg. So we have a deadlock case here:
Here are the stacks:
The solution is to pass txg returned by spa_vdev_enter(spa) at the top of spa_vdev_attach() to vdev_rebuild() and call dmu_tx_create_assigned(txg) which doesn't wait for txg.
How Has This Been Tested?
zfs-tests.sh -T redundancytests have passed.Types of changes
Checklist:
Signed-off-by.Closes #18210.