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88d012a1d6
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
122 lines
3.9 KiB
C
122 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 (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
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* Copyright 2011 Nexenta Systems, Inc. All rights reserved.
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* Copyright (c) 2012, 2018 by Delphix. All rights reserved.
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* Copyright (c) 2012, Joyent, Inc. All rights reserved.
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*/
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#ifndef _SYS_TASKQ_H
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#define _SYS_TASKQ_H
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#include <pthread.h>
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#include <stdint.h>
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#include <sys/kmem.h>
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#include <sys/thread.h>
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#include <sys/mutex.h>
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#include <sys/rwlock.h>
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#include <sys/condvar.h>
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/*
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* Task queues
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*/
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#define TASKQ_NAMELEN 31
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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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struct taskq_ent *tqent_next;
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struct taskq_ent *tqent_prev;
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task_func_t *tqent_func;
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void *tqent_arg;
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uintptr_t tqent_flags;
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} taskq_ent_t;
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typedef struct taskq {
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char tq_name[TASKQ_NAMELEN + 1];
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kmutex_t tq_lock;
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krwlock_t tq_threadlock;
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kcondvar_t tq_dispatch_cv;
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kcondvar_t tq_wait_cv;
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kthread_t **tq_threadlist;
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int tq_flags;
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int tq_active;
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int tq_nthreads;
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int tq_nalloc;
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int tq_minalloc;
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int tq_maxalloc;
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kcondvar_t tq_maxalloc_cv;
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int tq_maxalloc_wait;
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taskq_ent_t *tq_freelist;
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taskq_ent_t tq_task;
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} taskq_t;
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#define TQENT_FLAG_PREALLOC 0x1 /* taskq_dispatch_ent used */
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#define TASKQ_PREPOPULATE 0x0001
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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 /* Scale # threads by # cpus */
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#define TASKQ_DC_BATCH 0x0010 /* Mark threads as batch */
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#define TQ_SLEEP KM_SLEEP /* Can block for memory */
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#define TQ_NOSLEEP KM_NOSLEEP /* 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_FRONT 0x08 /* Queue in front */
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#define TASKQID_INVALID ((taskqid_t)0)
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extern taskq_t *_system_taskq(void);
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extern taskq_t *_system_delay_taskq(void);
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#define system_taskq _system_taskq()
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#define system_delay_taskq _system_delay_taskq()
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extern taskq_t *taskq_create(const char *, int, pri_t, int, int, uint_t);
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extern taskq_t *taskq_create_synced(const char *, int, pri_t, int, int, uint_t,
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kthread_t ***);
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#define taskq_create_proc(a, b, c, d, e, p, f) \
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(taskq_create(a, b, c, d, e, f))
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#define taskq_create_sysdc(a, b, d, e, p, dc, f) \
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((void) sizeof (dc), taskq_create(a, b, maxclsyspri, d, e, f))
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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 *, uint_t,
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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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extern void taskq_destroy(taskq_t *);
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extern void taskq_wait(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 int taskq_member(taskq_t *, kthread_t *);
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extern taskq_t *taskq_of_curthread(void);
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extern int taskq_cancel_id(taskq_t *, taskqid_t, boolean_t);
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extern void system_taskq_init(void);
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extern void system_taskq_fini(void);
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#endif /* _SYS_TASKQ_H */
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