Ameer Hamza 0bcbee6040 Fix snapshot automount race causing duplicate mounts and AVL tree panic ... Multiple threads racing to automount the same snapshot can both spawn mount helper processes that successfully complete, causing both parent threads to attempt AVL tree registration and triggering a VERIFY() panic in avl_add(). This occurs because the fsconfig/fsmount API lacks the serialization provided by traditional mount() via lock_mount(). The fix adds a per-entry mutex (se_mtx) to zfs_snapentry_t that serializes mount and unmount operations on the same snapshot. The first mount thread creates a pending entry with se_spa=NULL and holds se_mtx during the helper execution. Concurrent mounts find the pending entry and return success without spawning duplicate helpers. Unmount waits on se_mtx if a mount is pending, ensuring proper serialization. This allows different snapshots to mount in parallel while preventing the AVL panic. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com> Signed-off-by: Ameer Hamza <ahamza@ixsystems.com> Closes #17943		2025-12-10 10:21:29 -08:00
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freebsd	Fix snapshot automount expiry cancellation deadlock	2025-12-10 10:21:29 -08:00
linux	Fix snapshot automount race causing duplicate mounts and AVL tree panic	2025-12-10 10:21:29 -08:00