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A deadlock occurs when snapshot expiry tasks are cancelled while holding locks. The snapshot expiry task (snapentry_expire) spawns an umount process and waits for it to complete. Concurrently, ARC memory pressure triggers arc_prune which calls zfs_exit_fs(), attempting to cancel the expiry task while holding locks. The umount process spawned by the expiry task blocks trying to acquire locks held by arc_prune, which is blocked waiting for the expiry task to complete. This creates a circular dependency: expiry task waits for umount, umount waits for arc_prune, arc_prune waits for expiry task. Fix by adding non-blocking cancellation support to taskq_cancel_id(). The zfs_exit_fs() path calls zfsctl_snapshot_unmount_delay() to reschedule the unmount, which needs to cancel any existing expiry task. It now uses non-blocking cancellation to avoid waiting while holding locks, breaking the deadlock by returning immediately when the task is already running. The per-entry se_taskqid_lock has been removed, with all taskqid operations now protected by the global zfs_snapshot_lock held as WRITER. Additionally, an se_in_umount flag prevents recursive waits when zfsctl_destroy() is called during unmount. The taskqid is now only cleared by the caller on successful cancellation; running tasks clear their own taskqid upon completion. Reviewed-by: Alexander Motin <alexander.motin@TrueNAS.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Ameer Hamza <ahamza@ixsystems.com> Closes #17941 |
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| os | ||
| sys | ||
| .gitignore | ||
| cityhash.h | ||
| libnvpair.h | ||
| libuutil_common.h | ||
| libuutil_impl.h | ||
| libuutil.h | ||
| libzdb.h | ||
| libzfs_core.h | ||
| libzfs.h | ||
| libzfsbootenv.h | ||
| libzutil.h | ||
| Makefile.am | ||
| thread_pool.h | ||
| zfeature_common.h | ||
| zfs_comutil.h | ||
| zfs_crrd.h | ||
| zfs_deleg.h | ||
| zfs_fletcher.h | ||
| zfs_namecheck.h | ||
| zfs_prop.h | ||
| zfs_valstr.h | ||