* Possible KCSAN/lockdep issue in -next barns
@ 2026-01-21 5:41 Paul E. McKenney
2026-01-21 7:06 ` Harry Yoo
0 siblings, 1 reply; 7+ messages in thread
From: Paul E. McKenney @ 2026-01-21 5:41 UTC (permalink / raw)
To: Vlastimil Babka; +Cc: linux-mm
Hello, Vlastimil,
On the off-chance that this is useful new news. This happened in
rcutorture's TREE04 scenario running with KCSAN and lockdep enabled.
Thoughts?
Thanx, Paul
------------------------------------------------------------------------
[ 253.872153] =============================
[ 253.872271] [ BUG: Invalid wait context ]
[ 253.872271] 6.19.0-rc6-next-20260120 #21508 Not tainted
[ 253.875774] -----------------------------
[ 253.877983] migration/1/23 is trying to lock:
[ 253.877983] ffff8afd01054e98 (&barn->lock){..-.}-{3:3}, at: barn_get_empty_sheaf+0x1d/0xb0
[ 253.877983] other info that might help us debug this:
[ 253.877983] context-{5:5}
[ 253.877983] 3 locks held by migration/1/23:
[ 253.877983] #0: ffff8afd01fd89a8 (&p->pi_lock){-.-.}-{2:2}, at: __balance_push_cpu_stop+0x3f/0x200
[ 253.877983] #1: ffffffff9f15c5c8 (rcu_read_lock){....}-{1:3}, at: cpuset_cpus_allowed_fallback+0x27/0x250
[ 253.877983] #2: ffff8afd1f470be0 ((local_lock_t *)&pcs->lock){+.+.}-{3:3}, at: __kfree_rcu_sheaf+0x52/0x3d0
[ 253.877983] stack backtrace:
[ 253.877983] CPU: 1 UID: 0 PID: 23 Comm: migration/1 Not tainted 6.19.0-rc6-next-20260120 #21508 PREEMPTLAZY
[ 253.877983] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 253.877983] Stopper: __balance_push_cpu_stop+0x0/0x200 <- balance_push+0x118/0x170
[ 253.877983] Call Trace:
[ 253.877983] <TASK>
[ 253.877983] __dump_stack+0x22/0x30
[ 253.877983] dump_stack_lvl+0x60/0x80
[ 253.877983] dump_stack+0x19/0x24
[ 253.877983] __lock_acquire+0xd3a/0x28e0
[ 253.877983] ? __lock_acquire+0x5a9/0x28e0
[ 253.877983] ? __lock_acquire+0x5a9/0x28e0
[ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
[ 253.877983] lock_acquire+0xc3/0x270
[ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
[ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
[ 253.877983] _raw_spin_lock_irqsave+0x47/0x70
[ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
[ 253.877983] barn_get_empty_sheaf+0x1d/0xb0
[ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
[ 253.877983] __kfree_rcu_sheaf+0x19f/0x3d0
[ 253.877983] kvfree_call_rcu+0xaf/0x390
[ 253.877983] set_cpus_allowed_force+0xc8/0xf0
[ 253.877983] ? cpuset_cpus_allowed_fallback+0x27/0x250
[ 253.877983] cpuset_cpus_allowed_fallback+0x15d/0x250
[ 253.877983] select_fallback_rq+0x1d8/0x250
[ 253.877983] ? __pfx___balance_push_cpu_stop+0x10/0x10
[ 253.877983] __balance_push_cpu_stop+0x4f/0x200
[ 253.877983] cpu_stopper_thread+0x147/0x210
[ 253.877983] ? __pfx_cpu_stopper_thread+0x10/0x10
[ 253.877983] smpboot_thread_fn+0x24c/0x390
[ 253.877983] ? __pfx_smpboot_thread_fn+0x10/0x10
[ 253.877983] kthread+0x1fa/0x230
[ 253.877983] ? __pfx_smpboot_thread_fn+0x10/0x10
[ 253.877983] ? __pfx_kthread+0x10/0x10
[ 253.877983] ret_from_fork+0x157/0x2c0
[ 253.877983] ? __pfx_kthread+0x10/0x10
[ 253.877983] ret_from_fork_asm+0x1a/0x30
[ 253.877983] </TASK>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Possible KCSAN/lockdep issue in -next barns
2026-01-21 5:41 Possible KCSAN/lockdep issue in -next barns Paul E. McKenney
@ 2026-01-21 7:06 ` Harry Yoo
2026-01-21 7:16 ` Vlastimil Babka
2026-01-21 7:17 ` Harry Yoo
0 siblings, 2 replies; 7+ messages in thread
From: Harry Yoo @ 2026-01-21 7:06 UTC (permalink / raw)
To: Paul E. McKenney; +Cc: Vlastimil Babka, linux-mm
On Tue, Jan 20, 2026 at 09:41:14PM -0800, Paul E. McKenney wrote:
> Hello, Vlastimil,
>
> On the off-chance that this is useful new news. This happened in
> rcutorture's TREE04 scenario running with KCSAN and lockdep enabled.
>
> Thoughts?
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> [ 253.872153] =============================
> [ 253.872271] [ BUG: Invalid wait context ]
> [ 253.872271] 6.19.0-rc6-next-20260120 #21508 Not tainted
> [ 253.875774] -----------------------------
> [ 253.877983] migration/1/23 is trying to lock:
> [ 253.877983] ffff8afd01054e98 (&barn->lock){..-.}-{3:3}, at: barn_get_empty_sheaf+0x1d/0xb0
> [ 253.877983] other info that might help us debug this:
> [ 253.877983] context-{5:5}
> [ 253.877983] 3 locks held by migration/1/23:
> [ 253.877983] #0: ffff8afd01fd89a8 (&p->pi_lock){-.-.}-{2:2}, at: __balance_push_cpu_stop+0x3f/0x200
> [ 253.877983] #1: ffffffff9f15c5c8 (rcu_read_lock){....}-{1:3}, at: cpuset_cpus_allowed_fallback+0x27/0x250
> [ 253.877983] #2: ffff8afd1f470be0 ((local_lock_t *)&pcs->lock){+.+.}-{3:3}, at: __kfree_rcu_sheaf+0x52/0x3d0
> [ 253.877983] stack backtrace:
> [ 253.877983] CPU: 1 UID: 0 PID: 23 Comm: migration/1 Not tainted 6.19.0-rc6-next-20260120 #21508 PREEMPTLAZY
> [ 253.877983] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
> [ 253.877983] Stopper: __balance_push_cpu_stop+0x0/0x200 <- balance_push+0x118/0x170
> [ 253.877983] Call Trace:
> [ 253.877983] <TASK>
> [ 253.877983] __dump_stack+0x22/0x30
> [ 253.877983] dump_stack_lvl+0x60/0x80
> [ 253.877983] dump_stack+0x19/0x24
> [ 253.877983] __lock_acquire+0xd3a/0x28e0
> [ 253.877983] ? __lock_acquire+0x5a9/0x28e0
> [ 253.877983] ? __lock_acquire+0x5a9/0x28e0
> [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> [ 253.877983] lock_acquire+0xc3/0x270
> [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> [ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
> [ 253.877983] _raw_spin_lock_irqsave+0x47/0x70
> [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> [ 253.877983] barn_get_empty_sheaf+0x1d/0xb0
> [ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
> [ 253.877983] __kfree_rcu_sheaf+0x19f/0x3d0
> [ 253.877983] kvfree_call_rcu+0xaf/0x390
> [ 253.877983] set_cpus_allowed_force+0xc8/0xf0
set_cpus_allowed_force() is calling kfree_rcu() with a raw spinlock
(pi_lock) held, but barn->lock is normal spinlock, lockdep prints an
error because on PREEMPT_RT normal spinlocks are converted to
sleeping locks but raw spinlocks are not.
Hmm... but it isn't great to convert barn->lock to
a raw spinlock just because of this?
> [ 253.877983] ? cpuset_cpus_allowed_fallback+0x27/0x250
> [ 253.877983] cpuset_cpus_allowed_fallback+0x15d/0x250
> [ 253.877983] select_fallback_rq+0x1d8/0x250
> [ 253.877983] ? __pfx___balance_push_cpu_stop+0x10/0x10
> [ 253.877983] __balance_push_cpu_stop+0x4f/0x200
> [ 253.877983] cpu_stopper_thread+0x147/0x210
> [ 253.877983] ? __pfx_cpu_stopper_thread+0x10/0x10
> [ 253.877983] smpboot_thread_fn+0x24c/0x390
> [ 253.877983] ? __pfx_smpboot_thread_fn+0x10/0x10
> [ 253.877983] kthread+0x1fa/0x230
> [ 253.877983] ? __pfx_smpboot_thread_fn+0x10/0x10
> [ 253.877983] ? __pfx_kthread+0x10/0x10
> [ 253.877983] ret_from_fork+0x157/0x2c0
> [ 253.877983] ? __pfx_kthread+0x10/0x10
> [ 253.877983] ret_from_fork_asm+0x1a/0x30
> [ 253.877983] </TASK>
--
Cheers,
Harry / Hyeonggon
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Possible KCSAN/lockdep issue in -next barns
2026-01-21 7:06 ` Harry Yoo
@ 2026-01-21 7:16 ` Vlastimil Babka
2026-01-21 7:17 ` Harry Yoo
1 sibling, 0 replies; 7+ messages in thread
From: Vlastimil Babka @ 2026-01-21 7:16 UTC (permalink / raw)
To: Harry Yoo, Paul E. McKenney; +Cc: linux-mm
On 1/21/26 08:06, Harry Yoo wrote:
> On Tue, Jan 20, 2026 at 09:41:14PM -0800, Paul E. McKenney wrote:
>> Hello, Vlastimil,
>>
>> On the off-chance that this is useful new news. This happened in
>> rcutorture's TREE04 scenario running with KCSAN and lockdep enabled.
>>
>> Thoughts?
>>
>> Thanx, Paul
>>
>> ------------------------------------------------------------------------
>>
>> [ 253.872153] =============================
>> [ 253.872271] [ BUG: Invalid wait context ]
>> [ 253.872271] 6.19.0-rc6-next-20260120 #21508 Not tainted
>> [ 253.875774] -----------------------------
>> [ 253.877983] migration/1/23 is trying to lock:
>> [ 253.877983] ffff8afd01054e98 (&barn->lock){..-.}-{3:3}, at: barn_get_empty_sheaf+0x1d/0xb0
>> [ 253.877983] other info that might help us debug this:
>> [ 253.877983] context-{5:5}
>> [ 253.877983] 3 locks held by migration/1/23:
>> [ 253.877983] #0: ffff8afd01fd89a8 (&p->pi_lock){-.-.}-{2:2}, at: __balance_push_cpu_stop+0x3f/0x200
>> [ 253.877983] #1: ffffffff9f15c5c8 (rcu_read_lock){....}-{1:3}, at: cpuset_cpus_allowed_fallback+0x27/0x250
>> [ 253.877983] #2: ffff8afd1f470be0 ((local_lock_t *)&pcs->lock){+.+.}-{3:3}, at: __kfree_rcu_sheaf+0x52/0x3d0
>> [ 253.877983] stack backtrace:
>> [ 253.877983] CPU: 1 UID: 0 PID: 23 Comm: migration/1 Not tainted 6.19.0-rc6-next-20260120 #21508 PREEMPTLAZY
>> [ 253.877983] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
>> [ 253.877983] Stopper: __balance_push_cpu_stop+0x0/0x200 <- balance_push+0x118/0x170
>> [ 253.877983] Call Trace:
>> [ 253.877983] <TASK>
>> [ 253.877983] __dump_stack+0x22/0x30
>> [ 253.877983] dump_stack_lvl+0x60/0x80
>> [ 253.877983] dump_stack+0x19/0x24
>> [ 253.877983] __lock_acquire+0xd3a/0x28e0
>> [ 253.877983] ? __lock_acquire+0x5a9/0x28e0
>> [ 253.877983] ? __lock_acquire+0x5a9/0x28e0
>> [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
>> [ 253.877983] lock_acquire+0xc3/0x270
>> [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
>> [ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
>> [ 253.877983] _raw_spin_lock_irqsave+0x47/0x70
>> [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
>> [ 253.877983] barn_get_empty_sheaf+0x1d/0xb0
>> [ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
>> [ 253.877983] __kfree_rcu_sheaf+0x19f/0x3d0
>> [ 253.877983] kvfree_call_rcu+0xaf/0x390
>> [ 253.877983] set_cpus_allowed_force+0xc8/0xf0
>
> set_cpus_allowed_force() is calling kfree_rcu() with a raw spinlock
> (pi_lock) held, but barn->lock is normal spinlock, lockdep prints an
> error because on PREEMPT_RT normal spinlocks are converted to
> sleeping locks but raw spinlocks are not.
Hm right, Ulad did raise this issue and thus I made kvfree_call_rcu() skip
the kfree_rcu_sheaf() attempt on CONFIG_PREEMPT_RT.
But I forgot that lockdep (or a related debugging option) checks this
context even with !PREEMPT_RT.
We could skip kfree_rcu_sheaf() when this debugging is enabled? Not ideal.
Is there a way to detect such a context on runtime and only skip
kfree_rcu_sheaf() when really necessary?
> Hmm... but it isn't great to convert barn->lock to
> a raw spinlock just because of this?
>
>> [ 253.877983] ? cpuset_cpus_allowed_fallback+0x27/0x250
>> [ 253.877983] cpuset_cpus_allowed_fallback+0x15d/0x250
>> [ 253.877983] select_fallback_rq+0x1d8/0x250
>> [ 253.877983] ? __pfx___balance_push_cpu_stop+0x10/0x10
>> [ 253.877983] __balance_push_cpu_stop+0x4f/0x200
>> [ 253.877983] cpu_stopper_thread+0x147/0x210
>> [ 253.877983] ? __pfx_cpu_stopper_thread+0x10/0x10
>> [ 253.877983] smpboot_thread_fn+0x24c/0x390
>> [ 253.877983] ? __pfx_smpboot_thread_fn+0x10/0x10
>> [ 253.877983] kthread+0x1fa/0x230
>> [ 253.877983] ? __pfx_smpboot_thread_fn+0x10/0x10
>> [ 253.877983] ? __pfx_kthread+0x10/0x10
>> [ 253.877983] ret_from_fork+0x157/0x2c0
>> [ 253.877983] ? __pfx_kthread+0x10/0x10
>> [ 253.877983] ret_from_fork_asm+0x1a/0x30
>> [ 253.877983] </TASK>
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Possible KCSAN/lockdep issue in -next barns
2026-01-21 7:06 ` Harry Yoo
2026-01-21 7:16 ` Vlastimil Babka
@ 2026-01-21 7:17 ` Harry Yoo
2026-01-21 15:58 ` Paul E. McKenney
1 sibling, 1 reply; 7+ messages in thread
From: Harry Yoo @ 2026-01-21 7:17 UTC (permalink / raw)
To: Paul E. McKenney; +Cc: Vlastimil Babka, linux-mm
On Wed, Jan 21, 2026 at 04:06:25PM +0900, Harry Yoo wrote:
> On Tue, Jan 20, 2026 at 09:41:14PM -0800, Paul E. McKenney wrote:
> > Hello, Vlastimil,
> >
> > On the off-chance that this is useful new news. This happened in
> > rcutorture's TREE04 scenario running with KCSAN and lockdep enabled.
> >
> > Thoughts?
> >
> > Thanx, Paul
> >
> > ------------------------------------------------------------------------
> >
> > [ 253.872153] =============================
> > [ 253.872271] [ BUG: Invalid wait context ]
> > [ 253.872271] 6.19.0-rc6-next-20260120 #21508 Not tainted
> > [ 253.875774] -----------------------------
> > [ 253.877983] migration/1/23 is trying to lock:
> > [ 253.877983] ffff8afd01054e98 (&barn->lock){..-.}-{3:3}, at: barn_get_empty_sheaf+0x1d/0xb0
> > [ 253.877983] other info that might help us debug this:
> > [ 253.877983] context-{5:5}
> > [ 253.877983] 3 locks held by migration/1/23:
> > [ 253.877983] #0: ffff8afd01fd89a8 (&p->pi_lock){-.-.}-{2:2}, at: __balance_push_cpu_stop+0x3f/0x200
> > [ 253.877983] #1: ffffffff9f15c5c8 (rcu_read_lock){....}-{1:3}, at: cpuset_cpus_allowed_fallback+0x27/0x250
> > [ 253.877983] #2: ffff8afd1f470be0 ((local_lock_t *)&pcs->lock){+.+.}-{3:3}, at: __kfree_rcu_sheaf+0x52/0x3d0
> > [ 253.877983] stack backtrace:
> > [ 253.877983] CPU: 1 UID: 0 PID: 23 Comm: migration/1 Not tainted 6.19.0-rc6-next-20260120 #21508 PREEMPTLAZY
> > [ 253.877983] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
> > [ 253.877983] Stopper: __balance_push_cpu_stop+0x0/0x200 <- balance_push+0x118/0x170
> > [ 253.877983] Call Trace:
> > [ 253.877983] <TASK>
> > [ 253.877983] __dump_stack+0x22/0x30
> > [ 253.877983] dump_stack_lvl+0x60/0x80
> > [ 253.877983] dump_stack+0x19/0x24
> > [ 253.877983] __lock_acquire+0xd3a/0x28e0
> > [ 253.877983] ? __lock_acquire+0x5a9/0x28e0
> > [ 253.877983] ? __lock_acquire+0x5a9/0x28e0
> > [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> > [ 253.877983] lock_acquire+0xc3/0x270
> > [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> > [ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
> > [ 253.877983] _raw_spin_lock_irqsave+0x47/0x70
> > [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> > [ 253.877983] barn_get_empty_sheaf+0x1d/0xb0
> > [ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
> > [ 253.877983] __kfree_rcu_sheaf+0x19f/0x3d0
> > [ 253.877983] kvfree_call_rcu+0xaf/0x390
> > [ 253.877983] set_cpus_allowed_force+0xc8/0xf0
>
> set_cpus_allowed_force() is calling kfree_rcu() with a raw spinlock
> (pi_lock) held, but barn->lock is normal spinlock, lockdep prints an
> error because on PREEMPT_RT normal spinlocks are converted to
> sleeping locks but raw spinlocks are not.
>
> Hmm... but it isn't great to convert barn->lock to
> a raw spinlock just because of this?
No, on PREEMPT_RT kfree_call_rcu() doesn't use sheaves.
Is it benign and it's simply due to PROVE_RAW_LOCK_NESTING?
> > [ 253.877983] ? cpuset_cpus_allowed_fallback+0x27/0x250
> > [ 253.877983] cpuset_cpus_allowed_fallback+0x15d/0x250
> > [ 253.877983] select_fallback_rq+0x1d8/0x250
> > [ 253.877983] ? __pfx___balance_push_cpu_stop+0x10/0x10
> > [ 253.877983] __balance_push_cpu_stop+0x4f/0x200
> > [ 253.877983] cpu_stopper_thread+0x147/0x210
> > [ 253.877983] ? __pfx_cpu_stopper_thread+0x10/0x10
> > [ 253.877983] smpboot_thread_fn+0x24c/0x390
> > [ 253.877983] ? __pfx_smpboot_thread_fn+0x10/0x10
> > [ 253.877983] kthread+0x1fa/0x230
> > [ 253.877983] ? __pfx_smpboot_thread_fn+0x10/0x10
> > [ 253.877983] ? __pfx_kthread+0x10/0x10
> > [ 253.877983] ret_from_fork+0x157/0x2c0
> > [ 253.877983] ? __pfx_kthread+0x10/0x10
> > [ 253.877983] ret_from_fork_asm+0x1a/0x30
> > [ 253.877983] </TASK>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Possible KCSAN/lockdep issue in -next barns
2026-01-21 7:17 ` Harry Yoo
@ 2026-01-21 15:58 ` Paul E. McKenney
2026-01-22 1:24 ` Harry Yoo
0 siblings, 1 reply; 7+ messages in thread
From: Paul E. McKenney @ 2026-01-21 15:58 UTC (permalink / raw)
To: Harry Yoo; +Cc: Vlastimil Babka, linux-mm
On Wed, Jan 21, 2026 at 04:17:24PM +0900, Harry Yoo wrote:
> On Wed, Jan 21, 2026 at 04:06:25PM +0900, Harry Yoo wrote:
> > On Tue, Jan 20, 2026 at 09:41:14PM -0800, Paul E. McKenney wrote:
> > > Hello, Vlastimil,
> > >
> > > On the off-chance that this is useful new news. This happened in
> > > rcutorture's TREE04 scenario running with KCSAN and lockdep enabled.
> > >
> > > Thoughts?
> > >
> > > Thanx, Paul
> > >
> > > ------------------------------------------------------------------------
> > >
> > > [ 253.872153] =============================
> > > [ 253.872271] [ BUG: Invalid wait context ]
> > > [ 253.872271] 6.19.0-rc6-next-20260120 #21508 Not tainted
> > > [ 253.875774] -----------------------------
> > > [ 253.877983] migration/1/23 is trying to lock:
> > > [ 253.877983] ffff8afd01054e98 (&barn->lock){..-.}-{3:3}, at: barn_get_empty_sheaf+0x1d/0xb0
> > > [ 253.877983] other info that might help us debug this:
> > > [ 253.877983] context-{5:5}
> > > [ 253.877983] 3 locks held by migration/1/23:
> > > [ 253.877983] #0: ffff8afd01fd89a8 (&p->pi_lock){-.-.}-{2:2}, at: __balance_push_cpu_stop+0x3f/0x200
> > > [ 253.877983] #1: ffffffff9f15c5c8 (rcu_read_lock){....}-{1:3}, at: cpuset_cpus_allowed_fallback+0x27/0x250
> > > [ 253.877983] #2: ffff8afd1f470be0 ((local_lock_t *)&pcs->lock){+.+.}-{3:3}, at: __kfree_rcu_sheaf+0x52/0x3d0
> > > [ 253.877983] stack backtrace:
> > > [ 253.877983] CPU: 1 UID: 0 PID: 23 Comm: migration/1 Not tainted 6.19.0-rc6-next-20260120 #21508 PREEMPTLAZY
> > > [ 253.877983] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
> > > [ 253.877983] Stopper: __balance_push_cpu_stop+0x0/0x200 <- balance_push+0x118/0x170
> > > [ 253.877983] Call Trace:
> > > [ 253.877983] <TASK>
> > > [ 253.877983] __dump_stack+0x22/0x30
> > > [ 253.877983] dump_stack_lvl+0x60/0x80
> > > [ 253.877983] dump_stack+0x19/0x24
> > > [ 253.877983] __lock_acquire+0xd3a/0x28e0
> > > [ 253.877983] ? __lock_acquire+0x5a9/0x28e0
> > > [ 253.877983] ? __lock_acquire+0x5a9/0x28e0
> > > [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> > > [ 253.877983] lock_acquire+0xc3/0x270
> > > [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> > > [ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
> > > [ 253.877983] _raw_spin_lock_irqsave+0x47/0x70
> > > [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> > > [ 253.877983] barn_get_empty_sheaf+0x1d/0xb0
> > > [ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
> > > [ 253.877983] __kfree_rcu_sheaf+0x19f/0x3d0
> > > [ 253.877983] kvfree_call_rcu+0xaf/0x390
> > > [ 253.877983] set_cpus_allowed_force+0xc8/0xf0
> >
> > set_cpus_allowed_force() is calling kfree_rcu() with a raw spinlock
> > (pi_lock) held, but barn->lock is normal spinlock, lockdep prints an
> > error because on PREEMPT_RT normal spinlocks are converted to
> > sleeping locks but raw spinlocks are not.
> >
> > Hmm... but it isn't great to convert barn->lock to
> > a raw spinlock just because of this?
>
> No, on PREEMPT_RT kfree_call_rcu() doesn't use sheaves.
> Is it benign and it's simply due to PROVE_RAW_LOCK_NESTING?
Unless your kernel is built with CONFIG_PREEMPT_RT=y, in which case it
is a real bug that could call schedule() with preemption disabled.
Thanx, Paul
> > > [ 253.877983] ? cpuset_cpus_allowed_fallback+0x27/0x250
> > > [ 253.877983] cpuset_cpus_allowed_fallback+0x15d/0x250
> > > [ 253.877983] select_fallback_rq+0x1d8/0x250
> > > [ 253.877983] ? __pfx___balance_push_cpu_stop+0x10/0x10
> > > [ 253.877983] __balance_push_cpu_stop+0x4f/0x200
> > > [ 253.877983] cpu_stopper_thread+0x147/0x210
> > > [ 253.877983] ? __pfx_cpu_stopper_thread+0x10/0x10
> > > [ 253.877983] smpboot_thread_fn+0x24c/0x390
> > > [ 253.877983] ? __pfx_smpboot_thread_fn+0x10/0x10
> > > [ 253.877983] kthread+0x1fa/0x230
> > > [ 253.877983] ? __pfx_smpboot_thread_fn+0x10/0x10
> > > [ 253.877983] ? __pfx_kthread+0x10/0x10
> > > [ 253.877983] ret_from_fork+0x157/0x2c0
> > > [ 253.877983] ? __pfx_kthread+0x10/0x10
> > > [ 253.877983] ret_from_fork_asm+0x1a/0x30
> > > [ 253.877983] </TASK>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Possible KCSAN/lockdep issue in -next barns
2026-01-21 15:58 ` Paul E. McKenney
@ 2026-01-22 1:24 ` Harry Yoo
2026-01-22 1:35 ` Paul E. McKenney
0 siblings, 1 reply; 7+ messages in thread
From: Harry Yoo @ 2026-01-22 1:24 UTC (permalink / raw)
To: Paul E. McKenney; +Cc: Vlastimil Babka, linux-mm
On Wed, Jan 21, 2026 at 07:58:29AM -0800, Paul E. McKenney wrote:
> On Wed, Jan 21, 2026 at 04:17:24PM +0900, Harry Yoo wrote:
> > On Wed, Jan 21, 2026 at 04:06:25PM +0900, Harry Yoo wrote:
> > > On Tue, Jan 20, 2026 at 09:41:14PM -0800, Paul E. McKenney wrote:
> > > > Hello, Vlastimil,
> > > >
> > > > On the off-chance that this is useful new news. This happened in
> > > > rcutorture's TREE04 scenario running with KCSAN and lockdep enabled.
> > > >
> > > > Thoughts?
> > > >
> > > > Thanx, Paul
> > > >
> > > > ------------------------------------------------------------------------
> > > >
> > > > [ 253.872153] =============================
> > > > [ 253.872271] [ BUG: Invalid wait context ]
> > > > [ 253.872271] 6.19.0-rc6-next-20260120 #21508 Not tainted
> > > > [ 253.875774] -----------------------------
> > > > [ 253.877983] migration/1/23 is trying to lock:
> > > > [ 253.877983] ffff8afd01054e98 (&barn->lock){..-.}-{3:3}, at: barn_get_empty_sheaf+0x1d/0xb0
> > > > [ 253.877983] other info that might help us debug this:
> > > > [ 253.877983] context-{5:5}
> > > > [ 253.877983] 3 locks held by migration/1/23:
> > > > [ 253.877983] #0: ffff8afd01fd89a8 (&p->pi_lock){-.-.}-{2:2}, at: __balance_push_cpu_stop+0x3f/0x200
> > > > [ 253.877983] #1: ffffffff9f15c5c8 (rcu_read_lock){....}-{1:3}, at: cpuset_cpus_allowed_fallback+0x27/0x250
> > > > [ 253.877983] #2: ffff8afd1f470be0 ((local_lock_t *)&pcs->lock){+.+.}-{3:3}, at: __kfree_rcu_sheaf+0x52/0x3d0
> > > > [ 253.877983] stack backtrace:
> > > > [ 253.877983] CPU: 1 UID: 0 PID: 23 Comm: migration/1 Not tainted 6.19.0-rc6-next-20260120 #21508 PREEMPTLAZY
> > > > [ 253.877983] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
> > > > [ 253.877983] Stopper: __balance_push_cpu_stop+0x0/0x200 <- balance_push+0x118/0x170
> > > > [ 253.877983] Call Trace:
> > > > [ 253.877983] <TASK>
> > > > [ 253.877983] __dump_stack+0x22/0x30
> > > > [ 253.877983] dump_stack_lvl+0x60/0x80
> > > > [ 253.877983] dump_stack+0x19/0x24
> > > > [ 253.877983] __lock_acquire+0xd3a/0x28e0
> > > > [ 253.877983] ? __lock_acquire+0x5a9/0x28e0
> > > > [ 253.877983] ? __lock_acquire+0x5a9/0x28e0
> > > > [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> > > > [ 253.877983] lock_acquire+0xc3/0x270
> > > > [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> > > > [ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
> > > > [ 253.877983] _raw_spin_lock_irqsave+0x47/0x70
> > > > [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> > > > [ 253.877983] barn_get_empty_sheaf+0x1d/0xb0
> > > > [ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
> > > > [ 253.877983] __kfree_rcu_sheaf+0x19f/0x3d0
> > > > [ 253.877983] kvfree_call_rcu+0xaf/0x390
> > > > [ 253.877983] set_cpus_allowed_force+0xc8/0xf0
> > >
> > > set_cpus_allowed_force() is calling kfree_rcu() with a raw spinlock
> > > (pi_lock) held, but barn->lock is normal spinlock, lockdep prints an
> > > error because on PREEMPT_RT normal spinlocks are converted to
> > > sleeping locks but raw spinlocks are not.
> > >
> > > Hmm... but it isn't great to convert barn->lock to
> > > a raw spinlock just because of this?
> >
> > No, on PREEMPT_RT kfree_call_rcu() doesn't use sheaves.
> > Is it benign and it's simply due to PROVE_RAW_LOCK_NESTING?
>
> Unless your kernel is built with CONFIG_PREEMPT_RT=y, in which case it
> is a real bug that could call schedule() with preemption disabled.
Right, but it's fine because this path is never called with
CONFIG_PREEMPT_RT=y. Yesterday sent a fix to suppress this warning.
Thanks for reporting it, Paul!
--
Cheers,
Harry / Hyeonggon
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: Possible KCSAN/lockdep issue in -next barns
2026-01-22 1:24 ` Harry Yoo
@ 2026-01-22 1:35 ` Paul E. McKenney
0 siblings, 0 replies; 7+ messages in thread
From: Paul E. McKenney @ 2026-01-22 1:35 UTC (permalink / raw)
To: Harry Yoo; +Cc: Vlastimil Babka, linux-mm
On Thu, Jan 22, 2026 at 10:24:32AM +0900, Harry Yoo wrote:
> On Wed, Jan 21, 2026 at 07:58:29AM -0800, Paul E. McKenney wrote:
> > On Wed, Jan 21, 2026 at 04:17:24PM +0900, Harry Yoo wrote:
> > > On Wed, Jan 21, 2026 at 04:06:25PM +0900, Harry Yoo wrote:
> > > > On Tue, Jan 20, 2026 at 09:41:14PM -0800, Paul E. McKenney wrote:
> > > > > Hello, Vlastimil,
> > > > >
> > > > > On the off-chance that this is useful new news. This happened in
> > > > > rcutorture's TREE04 scenario running with KCSAN and lockdep enabled.
> > > > >
> > > > > Thoughts?
> > > > >
> > > > > Thanx, Paul
> > > > >
> > > > > ------------------------------------------------------------------------
> > > > >
> > > > > [ 253.872153] =============================
> > > > > [ 253.872271] [ BUG: Invalid wait context ]
> > > > > [ 253.872271] 6.19.0-rc6-next-20260120 #21508 Not tainted
> > > > > [ 253.875774] -----------------------------
> > > > > [ 253.877983] migration/1/23 is trying to lock:
> > > > > [ 253.877983] ffff8afd01054e98 (&barn->lock){..-.}-{3:3}, at: barn_get_empty_sheaf+0x1d/0xb0
> > > > > [ 253.877983] other info that might help us debug this:
> > > > > [ 253.877983] context-{5:5}
> > > > > [ 253.877983] 3 locks held by migration/1/23:
> > > > > [ 253.877983] #0: ffff8afd01fd89a8 (&p->pi_lock){-.-.}-{2:2}, at: __balance_push_cpu_stop+0x3f/0x200
> > > > > [ 253.877983] #1: ffffffff9f15c5c8 (rcu_read_lock){....}-{1:3}, at: cpuset_cpus_allowed_fallback+0x27/0x250
> > > > > [ 253.877983] #2: ffff8afd1f470be0 ((local_lock_t *)&pcs->lock){+.+.}-{3:3}, at: __kfree_rcu_sheaf+0x52/0x3d0
> > > > > [ 253.877983] stack backtrace:
> > > > > [ 253.877983] CPU: 1 UID: 0 PID: 23 Comm: migration/1 Not tainted 6.19.0-rc6-next-20260120 #21508 PREEMPTLAZY
> > > > > [ 253.877983] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
> > > > > [ 253.877983] Stopper: __balance_push_cpu_stop+0x0/0x200 <- balance_push+0x118/0x170
> > > > > [ 253.877983] Call Trace:
> > > > > [ 253.877983] <TASK>
> > > > > [ 253.877983] __dump_stack+0x22/0x30
> > > > > [ 253.877983] dump_stack_lvl+0x60/0x80
> > > > > [ 253.877983] dump_stack+0x19/0x24
> > > > > [ 253.877983] __lock_acquire+0xd3a/0x28e0
> > > > > [ 253.877983] ? __lock_acquire+0x5a9/0x28e0
> > > > > [ 253.877983] ? __lock_acquire+0x5a9/0x28e0
> > > > > [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> > > > > [ 253.877983] lock_acquire+0xc3/0x270
> > > > > [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> > > > > [ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
> > > > > [ 253.877983] _raw_spin_lock_irqsave+0x47/0x70
> > > > > [ 253.877983] ? barn_get_empty_sheaf+0x1d/0xb0
> > > > > [ 253.877983] barn_get_empty_sheaf+0x1d/0xb0
> > > > > [ 253.877983] ? __kfree_rcu_sheaf+0x52/0x3d0
> > > > > [ 253.877983] __kfree_rcu_sheaf+0x19f/0x3d0
> > > > > [ 253.877983] kvfree_call_rcu+0xaf/0x390
> > > > > [ 253.877983] set_cpus_allowed_force+0xc8/0xf0
> > > >
> > > > set_cpus_allowed_force() is calling kfree_rcu() with a raw spinlock
> > > > (pi_lock) held, but barn->lock is normal spinlock, lockdep prints an
> > > > error because on PREEMPT_RT normal spinlocks are converted to
> > > > sleeping locks but raw spinlocks are not.
> > > >
> > > > Hmm... but it isn't great to convert barn->lock to
> > > > a raw spinlock just because of this?
> > >
> > > No, on PREEMPT_RT kfree_call_rcu() doesn't use sheaves.
> > > Is it benign and it's simply due to PROVE_RAW_LOCK_NESTING?
> >
> > Unless your kernel is built with CONFIG_PREEMPT_RT=y, in which case it
> > is a real bug that could call schedule() with preemption disabled.
>
> Right, but it's fine because this path is never called with
> CONFIG_PREEMPT_RT=y. Yesterday sent a fix to suppress this warning.
Ah, missed that, apologies!
> Thanks for reporting it, Paul!
Happy to help, whether with one "l" or two. ;-)
Thanx, Paul
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2026-01-22 1:35 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2026-01-21 5:41 Possible KCSAN/lockdep issue in -next barns Paul E. McKenney
2026-01-21 7:06 ` Harry Yoo
2026-01-21 7:16 ` Vlastimil Babka
2026-01-21 7:17 ` Harry Yoo
2026-01-21 15:58 ` Paul E. McKenney
2026-01-22 1:24 ` Harry Yoo
2026-01-22 1:35 ` Paul E. McKenney
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