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Ameer Hamza
b2602a400a
zfsctl_snapshot_mount() holds z_teardown_lock(R) across call_usermodehelper(), which spawns a mount process that needs namespace_sem(W) via move_mount. Reading /proc/self/mountinfo holds namespace_sem(R) and needs z_teardown_lock(R) via zpl_show_devname. When zfs_suspend_fs (from zfs recv or zfs rollback) queues z_teardown_lock(W), the rrwlock blocks new readers, completing the deadlock cycle. Fix by releasing z_teardown_lock(R) after gathering the dataset name and mount path, before any blocking operation. Everything after the release operates on local string copies or uses its own synchronization. The parent zfsvfs pointer remains valid because the caller holds a path reference to the automount trigger dentry. Releasing the lock allows zfs_suspend_fs to proceed concurrently with the mount helper, so dmu_objset_hold in zpl_get_tree can transiently fail with ENOENT during the clone swap. The mount helper fails, EISDIR is returned, and the VFS falls back to the ctldir stub (empty directory) until the next access retries. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com> Reviewed-by: Rob Norris <robn@despairlabs.com> Signed-off-by: Ameer Hamza <ahamza@ixsystems.com> Closes #18415