[PATCH v2 2/2] blktrace: switch trace spinlock to a raw spinlock

Wander Lairson Costa
2021-12-13T12:40:19Z

TRACE_EVENT disables preemption before calling the callback. Because of
that blktrace triggers the following bug under PREEMPT_RT:

BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:35
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 119, name: kworker/u2:2
5 locks held by kworker/u2:2/119:
#0: ffff8c2e4a88f538 ((wq_completion)xfs-cil/dm-0){+.+.}-{0:0}, at: process_one_work+0x200/0x450
#1: ffffab3840ac7e68 ((work_completion)(&cil->xc_push_work)){+.+.}-{0:0}, at: process_one_work+0x200/0x450
#2: ffff8c2e4a887128 (&cil->xc_ctx_lock){++++}-{3:3}, at: xlog_cil_push_work+0xb7/0x670 [xfs]
#3: ffffffffa6a63780 (rcu_read_lock){....}-{1:2}, at: blk_add_trace_bio+0x0/0x1f0
#4: ffffffffa6610620 (running_trace_lock){+.+.}-{2:2}, at: __blk_add_trace+0x3ef/0x480
Preemption disabled at:
[<ffffffffa4d35c05>] migrate_enable+0x45/0x140
CPU: 0 PID: 119 Comm: kworker/u2:2 Kdump: loaded Not tainted 5.14.0-25.rt21.25.light.el9.x86_64+debug #1
Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
Workqueue: xfs-cil/dm-0 xlog_cil_push_work [xfs]
Call Trace:
? migrate_enable+0x45/0x140
dump_stack_lvl+0x57/0x7d
___might_sleep.cold+0xe3/0xf7
rt_spin_lock+0x3a/0xd0
? __blk_add_trace+0x3ef/0x480
__blk_add_trace+0x3ef/0x480
blk_add_trace_bio+0x18d/0x1f0
trace_block_bio_queue+0xb5/0x150
submit_bio_checks+0x1f0/0x520
? sched_clock_cpu+0xb/0x100
submit_bio_noacct+0x30/0x1d0
? bio_associate_blkg+0x66/0x190
xlog_cil_push_work+0x1b6/0x670 [xfs]
? register_lock_class+0x43/0x4f0
? xfs_swap_extents+0x5f0/0x5f0 [xfs]
process_one_work+0x275/0x450
? process_one_work+0x200/0x450
worker_thread+0x55/0x3c0
? process_one_work+0x450/0x450
kthread+0x188/0x1a0
? set_kthread_struct+0x40/0x40
ret_from_fork+0x22/0x30

To avoid this bug, we switch the trace lock to a raw spinlock.

Signed-off-by: Wander Lairson Costa <wander@redhat.com>
---
kernel/trace/blktrace.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 1183c88634aa..a86e022f7155 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -34,7 +34,7 @@ static struct trace_array *blk_tr;
static bool blk_tracer_enabled __read_mostly;

static LIST_HEAD(running_trace_list);
-static __cacheline_aligned_in_smp DEFINE_SPINLOCK(running_trace_lock);
+static __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(running_trace_lock);

/* Select an alternative, minimalistic output than the original one */
#define TRACE_BLK_OPT_CLASSIC 0x1
@@ -121,12 +121,12 @@ static void trace_note_tsk(struct task_struct *tsk)
struct blk_trace *bt;

tsk->btrace_seq = blktrace_seq;
- spin_lock_irqsave(&running_trace_lock, flags);
+ raw_spin_lock_irqsave(&running_trace_lock, flags);
list_for_each_entry(bt, &running_trace_list, running_list) {
trace_note(bt, tsk->pid, BLK_TN_PROCESS, tsk->comm,
sizeof(tsk->comm), 0);
}
- spin_unlock_irqrestore(&running_trace_lock, flags);
+ raw_spin_unlock_irqrestore(&running_trace_lock, flags);
}

static void trace_note_time(struct blk_trace *bt)
@@ -666,9 +666,9 @@ static int __blk_trace_startstop(struct request_queue *q, int start)
blktrace_seq++;
smp_mb();
bt->trace_state = Blktrace_running;
- spin_lock_irq(&running_trace_lock);
+ raw_spin_lock_irq(&running_trace_lock);
list_add(&bt->running_list, &running_trace_list);
- spin_unlock_irq(&running_trace_lock);
+ raw_spin_unlock_irq(&running_trace_lock);

trace_note_time(bt);
ret = 0;
@@ -676,9 +676,9 @@ static int __blk_trace_startstop(struct request_queue *q, int start)
} else {
if (bt->trace_state == Blktrace_running) {
bt->trace_state = Blktrace_stopped;
- spin_lock_irq(&running_trace_lock);
+ raw_spin_lock_irq(&running_trace_lock);
list_del_init(&bt->running_list);
- spin_unlock_irq(&running_trace_lock);
+ raw_spin_unlock_irq(&running_trace_lock);
relay_flush(bt->rchan);
ret = 0;
}
@@ -1608,9 +1608,9 @@ static int blk_trace_remove_queue(struct request_queue *q)

if (bt->trace_state == Blktrace_running) {
bt->trace_state = Blktrace_stopped;
- spin_lock_irq(&running_trace_lock);
+ raw_spin_lock_irq(&running_trace_lock);
list_del_init(&bt->running_list);
- spin_unlock_irq(&running_trace_lock);
+ raw_spin_unlock_irq(&running_trace_lock);
relay_flush(bt->rchan);
}

--
2.27.0