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McKenney" To: Harry Yoo Cc: Vlastimil Babka , linux-mm@kvack.org Subject: Re: Possible KCSAN/lockdep issue in -next barns Message-ID: <55e3dd8f-1b56-4f83-8657-7583175de8f4@paulmck-laptop> Reply-To: paulmck@kernel.org References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: kfahjokdk8pqpc16yrgs9k3b53bhkogn X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0CF6A40007 X-HE-Tag: 1769011110-399242 X-HE-Meta: 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 mMCIh/WM 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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] > > > [ 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]