Comment 1 for bug 1847832

The fix in question is:

commit e7a2fa70c3b0d8c8cee2b484038bb5623c7c1ea9
Author: Tom Caputi <email address hidden>
Date: Tue Aug 27 12:55:51 2019 -0400

    Fix deadlock in 'zfs rollback'

    Currently, the 'zfs rollback' code can end up deadlocked due to
    the way the kernel handles unreferenced inodes on a suspended fs.
    Essentially, the zfs_resume_fs() code path may cause zfs to spawn
    new threads as it reinstantiates the suspended fs's zil. When a
    new thread is spawned, the kernel may attempt to free memory for
    that thread by freeing some unreferenced inodes. If it happens to
    select inodes that are a a part of the suspended fs a deadlock
    will occur because freeing inodes requires holding the fs's
    z_teardown_inactive_lock which is still held from the suspend.

    This patch corrects this issue by adding an additional reference
    to all inodes that are still present when a suspend is initiated.
    This prevents them from being freed by the kernel for any reason.

    Reviewed-by: Alek Pinchuk <email address hidden>
    Reviewed-by: Brian Behlendorf <email address hidden>
    Signed-off-by: Tom Caputi <email address hidden>
    Closes #9203