fs: quota: create dedicated workqueue for quota_release_work

There is a kernel panic due to WARN_ONCE when panic_on_warn is set.

This issue occurs when writeback is triggered due to sync call for an
opened file(ie, writeback reason is WB_REASON_SYNC). When f2fs balance
is needed at sync path, flush for quota_release_work is triggered.
By default quota_release_work is queued to "events_unbound" queue which
does not have WQ_MEM_RECLAIM flag. During f2fs balance "writeback"
workqueue tries to flush quota_release_work causing kernel panic due to
MEM_RECLAIM flag mismatch errors.

This patch creates dedicated workqueue with WQ_MEM_RECLAIM flag
for work quota_release_work.

------------[ cut here ]------------
WARNING: CPU: 4 PID: 14867 at kernel/workqueue.c:3721 check_flush_dependency+0x13c/0x148
Call trace:
 check_flush_dependency+0x13c/0x148
 __flush_work+0xd0/0x398
 flush_delayed_work+0x44/0x5c
 dquot_writeback_dquots+0x54/0x318
 f2fs_do_quota_sync+0xb8/0x1a8
 f2fs_write_checkpoint+0x3cc/0x99c
 f2fs_gc+0x190/0x750
 f2fs_balance_fs+0x110/0x168
 f2fs_write_single_data_page+0x474/0x7dc
 f2fs_write_data_pages+0x7d0/0xd0c
 do_writepages+0xe0/0x2f4
 __writeback_single_inode+0x44/0x4ac
 writeback_sb_inodes+0x30c/0x538
 wb_writeback+0xf4/0x440
 wb_workfn+0x128/0x5d4
 process_scheduled_works+0x1c4/0x45c
 worker_thread+0x32c/0x3e8
 kthread+0x11c/0x1b0
 ret_from_fork+0x10/0x20
Kernel panic - not syncing: kernel: panic_on_warn set ...

Fixes: ac6f420 ("quota: flush quota_release_work upon quota writeback")
CC: stable@vger.kernel.org
Signed-off-by: Shashank A P <shashank.ap@samsung.com>
Link: https://patch.msgid.link/20250901092905.2115-1-shashank.ap@samsung.com
Signed-off-by: Jan Kara <jack@suse.cz>

Author: Shashank A P

fs/quota/dquot.c

@@ -162,6 +162,9 @@ static struct quota_module_name module_names[] = INIT_QUOTA_MODULE_NAMES;
 /* SLAB cache for dquot structures */
 static struct kmem_cache *dquot_cachep;
 
+/* workqueue for work quota_release_work*/
+static struct workqueue_struct *quota_unbound_wq;
+
 void register_quota_format(struct quota_format_type *fmt)
 {
 	spin_lock(&dq_list_lock);
@@ -881,7 +884,7 @@ void dqput(struct dquot *dquot)
 	put_releasing_dquots(dquot);
 	atomic_dec(&dquot->dq_count);
 	spin_unlock(&dq_list_lock);
-	queue_delayed_work(system_unbound_wq, &quota_release_work, 1);
+	queue_delayed_work(quota_unbound_wq, &quota_release_work, 1);
 }
 EXPORT_SYMBOL(dqput);
 
@@ -3041,6 +3044,11 @@ static int __init dquot_init(void)
 
 	shrinker_register(dqcache_shrinker);
 
+	quota_unbound_wq = alloc_workqueue("quota_events_unbound",
+					   WQ_UNBOUND | WQ_MEM_RECLAIM, WQ_MAX_ACTIVE);
+	if (!quota_unbound_wq)
+		panic("Cannot create quota_unbound_wq\n");
+
 	return 0;
 }
 fs_initcall(dquot_init);