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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
130 lines
3.9 KiB
C
130 lines
3.9 KiB
C
// SPDX-License-Identifier: CDDL-1.0
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/*
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* CDDL HEADER START
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*
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* The contents of this file are subject to the terms of the
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* Common Development and Distribution License (the "License").
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* You may not use this file except in compliance with the License.
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*
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* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
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* or https://opensource.org/licenses/CDDL-1.0.
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* See the License for the specific language governing permissions
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* and limitations under the License.
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*
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* When distributing Covered Code, include this CDDL HEADER in each
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* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
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* If applicable, add the following below this CDDL HEADER, with the
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* fields enclosed by brackets "[]" replaced with your own identifying
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* information: Portions Copyright [yyyy] [name of copyright owner]
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*
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* CDDL HEADER END
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*/
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/*
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* Copyright 2009 Sun Microsystems, Inc. All rights reserved.
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* Use is subject to license terms.
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*/
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#ifndef _SYS_TASKQ_H
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#define _SYS_TASKQ_H
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#ifdef _KERNEL
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#include <sys/types.h>
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#include <sys/proc.h>
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#include <sys/queue.h>
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#include <sys/taskqueue.h>
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#include <sys/thread.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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#define TASKQ_NAMELEN 31
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typedef struct taskq {
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struct taskqueue *tq_queue;
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int tq_nthreads;
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} taskq_t;
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typedef uintptr_t taskqid_t;
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typedef void (task_func_t)(void *);
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typedef struct taskq_ent {
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union {
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struct task tqent_task;
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struct timeout_task tqent_timeout_task;
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};
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task_func_t *tqent_func;
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void *tqent_arg;
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taskqid_t tqent_id;
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LIST_ENTRY(taskq_ent) tqent_hash;
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uint_t tqent_type;
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volatile uint_t tqent_rc;
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} taskq_ent_t;
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/*
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* Public flags for taskq_create(): bit range 0-15
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*/
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#define TASKQ_PREPOPULATE 0x0001 /* Prepopulate with threads and data */
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#define TASKQ_CPR_SAFE 0x0002 /* Use CPR safe protocol */
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#define TASKQ_DYNAMIC 0x0004 /* Use dynamic thread scheduling */
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#define TASKQ_THREADS_CPU_PCT 0x0008 /* number of threads as % of ncpu */
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#define TASKQ_DC_BATCH 0x0010 /* Taskq uses SDC in batch mode */
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/*
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* Flags for taskq_dispatch. TQ_SLEEP/TQ_NOSLEEP should be same as
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* KM_SLEEP/KM_NOSLEEP.
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*/
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#define TQ_SLEEP 0x00 /* Can block for memory */
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#define TQ_NOSLEEP 0x01 /* cannot block for memory; may fail */
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#define TQ_NOQUEUE 0x02 /* Do not enqueue if can't dispatch */
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#define TQ_NOALLOC 0x04 /* cannot allocate memory; may fail */
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#define TQ_FRONT 0x08 /* Put task at the front of the queue */
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#define TASKQID_INVALID ((taskqid_t)0)
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extern taskq_t *system_taskq;
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/* Global dynamic task queue for long delay */
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extern taskq_t *system_delay_taskq;
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extern taskqid_t taskq_dispatch(taskq_t *, task_func_t, void *, uint_t);
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extern taskqid_t taskq_dispatch_delay(taskq_t *, task_func_t, void *,
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uint_t, clock_t);
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extern void taskq_dispatch_ent(taskq_t *, task_func_t, void *, uint_t,
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taskq_ent_t *);
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extern int taskq_empty_ent(taskq_ent_t *);
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extern void taskq_init_ent(taskq_ent_t *);
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taskq_t *taskq_create(const char *, int, pri_t, int, int, uint_t);
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taskq_t *taskq_create_synced(const char *, int, pri_t, int, int, uint_t,
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kthread_t ***);
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taskq_t *taskq_create_instance(const char *, int, int, pri_t, int, int, uint_t);
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taskq_t *taskq_create_proc(const char *, int, pri_t, int, int,
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struct proc *, uint_t);
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taskq_t *taskq_create_sysdc(const char *, int, int, int,
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struct proc *, uint_t, uint_t);
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void nulltask(void *);
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extern void taskq_destroy(taskq_t *);
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extern void taskq_wait_id(taskq_t *, taskqid_t);
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extern void taskq_wait_outstanding(taskq_t *, taskqid_t);
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extern void taskq_wait(taskq_t *);
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extern int taskq_cancel_id(taskq_t *, taskqid_t, boolean_t);
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extern int taskq_member(taskq_t *, kthread_t *);
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extern taskq_t *taskq_of_curthread(void);
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void taskq_suspend(taskq_t *);
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int taskq_suspended(taskq_t *);
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void taskq_resume(taskq_t *);
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#ifdef __cplusplus
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}
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#endif
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#endif /* _KERNEL */
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#ifdef _STANDALONE
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typedef void taskq_t;
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typedef int taskq_ent_t;
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#define taskq_init_ent(x)
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#endif /* _STANDALONE */
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#endif /* _SYS_TASKQ_H */
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