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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: Reply-To: paulmck@kernel.org References: <55e3dd8f-1b56-4f83-8657-7583175de8f4@paulmck-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Stat-Signature: tussr894mgjzq9zheo49so43f6nepo47 X-Rspamd-Queue-Id: 3A8512000A X-Rspam-User: X-HE-Tag: 1769045732-556561 X-HE-Meta: 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 Dvj9Q/HO 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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 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] > > > > > [ 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