From 19af457573838785290d27dd09a59140f541d1d8 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Thu, 11 Jul 2024 16:35:43 +0800 Subject: [PATCH] workqueue: Remove cpus_read_lock() from apply_wqattrs_lock() 1726a1713590 ("workqueue: Put PWQ allocation and WQ enlistment in the same lock C.S.") led to the following possible deadlock: WARNING: possible recursive locking detected 6.10.0-rc5-00004-g1d4c6111406c #1 Not tainted -------------------------------------------- swapper/0/1 is trying to acquire lock: c27760f4 (cpu_hotplug_lock){++++}-{0:0}, at: alloc_workqueue (kernel/workqueue.c:5152 kernel/workqueue.c:5730) but task is already holding lock: c27760f4 (cpu_hotplug_lock){++++}-{0:0}, at: padata_alloc (kernel/padata.c:1007) ... stack backtrace: ... cpus_read_lock (include/linux/percpu-rwsem.h:53 kernel/cpu.c:488) alloc_workqueue (kernel/workqueue.c:5152 kernel/workqueue.c:5730) padata_alloc (kernel/padata.c:1007 (discriminator 1)) pcrypt_init_padata (crypto/pcrypt.c:327 (discriminator 1)) pcrypt_init (crypto/pcrypt.c:353) do_one_initcall (init/main.c:1267) do_initcalls (init/main.c:1328 (discriminator 1) init/main.c:1345 (discriminator 1)) kernel_init_freeable (init/main.c:1364) kernel_init (init/main.c:1469) ret_from_fork (arch/x86/kernel/process.c:153) ret_from_fork_asm (arch/x86/entry/entry_32.S:737) entry_INT80_32 (arch/x86/entry/entry_32.S:944) This is caused by pcrypt allocating a workqueue while holding cpus_read_lock(), so workqueue code can't do it again as that can lead to deadlocks if down_write starts after the first down_read. The pwq creations and installations have been reworked based on wq_online_cpumask rather than cpu_online_mask making cpus_read_lock() is unneeded during wqattrs changes. Fix the deadlock by removing cpus_read_lock() from apply_wqattrs_lock(). tj: Updated changelog. Signed-off-by: Lai Jiangshan Fixes: 1726a1713590 ("workqueue: Put PWQ allocation and WQ enlistment in the same lock C.S.") Link: http://lkml.kernel.org/r/202407081521.83b627c1-lkp@intel.com Signed-off-by: Tejun Heo --- kernel/workqueue.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index a345a72395e7..9b7c1fcd934b 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -5113,15 +5113,12 @@ static struct pool_workqueue *alloc_unbound_pwq(struct workqueue_struct *wq, static void apply_wqattrs_lock(void) { - /* CPUs should stay stable across pwq creations and installations */ - cpus_read_lock(); mutex_lock(&wq_pool_mutex); } static void apply_wqattrs_unlock(void) { mutex_unlock(&wq_pool_mutex); - cpus_read_unlock(); } /**