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Subject[PATCH RT 2/4] workqueue: fixup rcu check for RT
Date
4.1.46-rt52-rc1 stable review patch.
If you have any objection to the inclusion of this patch, let me know.

--- 8< --- 8< --- 8< ---
Upstream commit 5b95e1af8d17d ("workqueue: wq_pool_mutex protects the
attrs-installation") introduced an additional assertion
(assert_rcu_or_wq_mutex_or_pool_mutex) which contains a check ensuring
that the caller is in a RCU-sched read-side critical section.

However, on RT, the locking rules are lessened to only require require
_normal_ RCU. Fix up this check.

The upstream commit was cherry-picked back into stable v4.1.19 as d3c4dd8843be.

This fixes up the bogus splat triggered on boot:

===============================
[ INFO: suspicious RCU usage. ]
4.1.42-rt50
-------------------------------
kernel/workqueue.c:609 sched RCU, wq->mutex or wq_pool_mutex should be held!

other info that might help us debug this:

rcu_scheduler_active = 1, debug_locks = 0
2 locks held by swapper/0/1:
#0: ((pendingb_lock).lock){+.+...}, at: queue_work_on+0x64/0x1c0
#1: (rcu_read_lock){......}, at: __queue_work+0x2a/0x880

stack backtrace:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.1.42-rt50 #4
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-20170228_101828-anatol 04/01/2014
Call Trace:
dump_stack+0x70/0x9a
lockdep_rcu_suspicious+0xe7/0x120
unbound_pwq_by_node+0x92/0x100
__queue_work+0x28c/0x880
? __queue_work+0x2a/0x880
queue_work_on+0xc9/0x1c0
call_usermodehelper_exec+0x1a7/0x200
kobject_uevent_env+0x4be/0x520
? initcall_blacklist+0xa2/0xa2
kobject_uevent+0xb/0x10
kset_register+0x34/0x50
bus_register+0x100/0x2d0
? ftrace_define_fields_workqueue_work+0x29/0x29
subsys_virtual_register+0x26/0x50
wq_sysfs_init+0x12/0x14
do_one_initcall+0x88/0x1b0
? parse_args+0x190/0x410
kernel_init_freeable+0x204/0x299
? rest_init+0x140/0x140
kernel_init+0x9/0xf0
ret_from_fork+0x42/0x70
? rest_init+0x140/0x140

Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Julia Cartwright <julia@ni.com>
---
kernel/workqueue.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 6bdcab98501c..90e261c8811e 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -363,7 +363,7 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
"RCU or wq->mutex should be held")

#define assert_rcu_or_wq_mutex_or_pool_mutex(wq) \
- rcu_lockdep_assert(rcu_read_lock_sched_held() || \
+ rcu_lockdep_assert(rcu_read_lock_held() || \
lockdep_is_held(&wq->mutex) || \
lockdep_is_held(&wq_pool_mutex), \
"sched RCU, wq->mutex or wq_pool_mutex should be held")
--
2.14.2
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