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Message-ID: <20250122191742.3025187-1-longman@redhat.com>
Date: Wed, 22 Jan 2025 14:17:42 -0500
From: Waiman Long <longman@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Will Deacon <will.deacon@....com>,
Boqun Feng <boqun.feng@...il.com>
Cc: linux-kernel@...r.kernel.org,
Waiman Long <longman@...hat.com>
Subject: [PATCH v2] locking/semaphore: Use wake_q to wake up processes outside lock critical section
A circular lock dependency splat has been seen involving down_trylock().
[ 4011.795602] ======================================================
[ 4011.795603] WARNING: possible circular locking dependency detected
[ 4011.795607] 6.12.0-41.el10.s390x+debug
[ 4011.795612] ------------------------------------------------------
[ 4011.795613] dd/32479 is trying to acquire lock:
[ 4011.795617] 0015a20accd0d4f8 ((console_sem).lock){-.-.}-{2:2}, at: down_trylock+0x26/0x90
[ 4011.795636]
[ 4011.795636] but task is already holding lock:
[ 4011.795637] 000000017e461698 (&zone->lock){-.-.}-{2:2}, at: rmqueue_bulk+0xac/0x8f0
the existing dependency chain (in reverse order) is:
-> #4 (&zone->lock){-.-.}-{2:2}:
-> #3 (hrtimer_bases.lock){-.-.}-{2:2}:
-> #2 (&rq->__lock){-.-.}-{2:2}:
-> #1 (&p->pi_lock){-.-.}-{2:2}:
-> #0 ((console_sem).lock){-.-.}-{2:2}:
The console_sem -> pi_lock dependency is due to calling try_to_wake_up()
while holding the console.sem raw_spinlock. This dependency can be broken
by using wake_q to do the wakeup instead of calling try_to_wake_up()
under the console_sem lock. This will also make the semaphore's
raw_spinlock become a terminal lock without taking any further locks
underneath it.
The hrtimer_bases.lock -> zone->lock dependency is actually another
instance of raw_spinlock to spinlock nesting problem.
[ 4011.795646] -> #4 (&zone->lock){-.-.}-{2:2}:
[ 4011.795650] __lock_acquire+0xe86/0x1cc0
[ 4011.795655] lock_acquire.part.0+0x258/0x630
[ 4011.795657] lock_acquire+0xb8/0xe0
[ 4011.795659] _raw_spin_lock_irqsave+0xb4/0x120
[ 4011.795663] rmqueue_bulk+0xac/0x8f0
[ 4011.795665] __rmqueue_pcplist+0x580/0x830
[ 4011.795667] rmqueue_pcplist+0xfc/0x470
[ 4011.795669] rmqueue.isra.0+0xdec/0x11b0
[ 4011.795671] get_page_from_freelist+0x2ee/0xeb0
[ 4011.795673] __alloc_pages_noprof+0x2c2/0x520
[ 4011.795676] alloc_pages_mpol_noprof+0x1fc/0x4d0
[ 4011.795681] alloc_pages_noprof+0x8c/0xe0
[ 4011.795684] allocate_slab+0x320/0x460
[ 4011.795686] ___slab_alloc+0xa58/0x12b0
[ 4011.795688] __slab_alloc.isra.0+0x42/0x60
[ 4011.795690] kmem_cache_alloc_noprof+0x304/0x350
[ 4011.795692] fill_pool+0xf6/0x450
[ 4011.795697] debug_object_activate+0xfe/0x360
[ 4011.795700] enqueue_hrtimer+0x34/0x190
[ 4011.795703] __run_hrtimer+0x3c8/0x4c0
[ 4011.795705] __hrtimer_run_queues+0x1b2/0x260
[ 4011.795707] hrtimer_interrupt+0x316/0x760
[ 4011.795709] do_IRQ+0x9a/0xe0
[ 4011.795712] do_irq_async+0xf6/0x160
We will need to make some changes in debugobjects and/or hrtimer code
to address this problem and break the circular dependency.
Anyway, semaphore is the only locking primitive left that is still
using try_to_wake_up() to do wakeup inside critical section, all the
other locking primitives had been migrated to use wake_q to do wakeup
outside of the critical section. It is also possible that there are
other circular locking dependencies involving printk/console_sem lurking
somewhere which may show up in the future. Let just do the migration
now to wake_q to avoid future headache like this.
Signed-off-by: Waiman Long <longman@...hat.com>
---
kernel/locking/semaphore.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c
index cb27cbf5162f..751e3cbb899f 100644
--- a/kernel/locking/semaphore.c
+++ b/kernel/locking/semaphore.c
@@ -29,6 +29,7 @@
#include <linux/export.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
+#include <linux/sched/wake_q.h>
#include <linux/semaphore.h>
#include <linux/spinlock.h>
#include <linux/ftrace.h>
@@ -38,7 +39,7 @@ static noinline void __down(struct semaphore *sem);
static noinline int __down_interruptible(struct semaphore *sem);
static noinline int __down_killable(struct semaphore *sem);
static noinline int __down_timeout(struct semaphore *sem, long timeout);
-static noinline void __up(struct semaphore *sem);
+static noinline void __up(struct semaphore *sem, struct wake_q_head *wake_q);
/**
* down - acquire the semaphore
@@ -185,13 +186,16 @@ EXPORT_SYMBOL(down_timeout);
void __sched up(struct semaphore *sem)
{
unsigned long flags;
+ DEFINE_WAKE_Q(wake_q);
raw_spin_lock_irqsave(&sem->lock, flags);
if (likely(list_empty(&sem->wait_list)))
sem->count++;
else
- __up(sem);
+ __up(sem, &wake_q);
raw_spin_unlock_irqrestore(&sem->lock, flags);
+ if (!wake_q_empty(&wake_q))
+ wake_up_q(&wake_q);
}
EXPORT_SYMBOL(up);
@@ -271,11 +275,12 @@ static noinline int __sched __down_timeout(struct semaphore *sem, long timeout)
return __down_common(sem, TASK_UNINTERRUPTIBLE, timeout);
}
-static noinline void __sched __up(struct semaphore *sem)
+static noinline void __sched __up(struct semaphore *sem,
+ struct wake_q_head *wake_q)
{
struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
struct semaphore_waiter, list);
list_del(&waiter->list);
waiter->up = true;
- wake_up_process(waiter->task);
+ wake_q_add(wake_q, waiter->task);
}
--
2.47.1
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