Re: [PATCH v2 6/7] mm, slab: call kvfree_rcu_barrier() from kmem_cache_destroy()

Keith Busch
2025-02-25T17:05:49Z

On Tue, Feb 25, 2025 at 09:03:38AM -0700, Keith Busch wrote:
> On Tue, Feb 25, 2025 at 10:57:38AM +0100, Vlastimil Babka wrote:
> > I tried to create a kunit test for it, but it doesn't trigger anything. Maybe
> > it's too simple, or racy, and thus we are not flushing any of the queues from
> > kvfree_rcu_barrier()?
>
> Thanks, your test readily triggers it for me, but only if I load
> rcutorture at the same time.

Oops, I sent the wrong kernel messages. This is the relevant part:

[ 142.371052] workqueue: WQ_MEM_RECLAIM
test_kfree_rcu_destroy_wq:cache_destroy_workfn [slub_kunit] is
flushing !WQ_MEM_RECLAIM events_unbound:kfree_rcu_work
[ 142.371072] WARNING: CPU: 11 PID: 186 at kernel/workqueue.c:3715
check_flush_dependency.part.0+0xad/0x100
[ 142.375748] Modules linked in: slub_kunit(E) rcutorture(E)
torture(E) kunit(E) iTCO_wdt(E) iTCO_vendor_support(E)
intel_uncore_frequency_common(E) skx_edac_common(E) nfit(E)
libnvdimm(E) kvm_intel(E) kvm(E) evdev(E) bochs(E) serio_raw(E)
drm_kms_helper(E) i2c_i801(E) e1000e(E) i2c_smbus(E) intel_agp(E)
intel_gtt(E) lpc_ich(E) agpgart(E) mfd_core(E) drm_shm]
[ 142.384553] CPU: 11 UID: 0 PID: 186 Comm: kworker/u64:11 Tainted: G
E N 6.13.0-04839-g5e7b40f0ddce-dirty #831
[ 142.386755] Tainted: [E]=UNSIGNED_MODULE, [N]=TEST
[ 142.387849] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009),
BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[ 142.390236] Workqueue: test_kfree_rcu_destroy_wq
cache_destroy_workfn [slub_kunit]
[ 142.391863] RIP: 0010:check_flush_dependency.part.0+0xad/0x100
[ 142.393183] Code: 75 dc 48 8b 55 18 49 8d 8d 78 01 00 00 4d 89 f0
48 81 c6 78 01 00 00 48 c7 c7 00 e1 9a 82 c6 05 4f 39 c5 02 01 e8 53
bd fd ff <0f> 0b 5b 5d 41 5c 41 5d 41 5e c3 80 3d 39 39 c5 02 00 75 83
41 8b
[ 142.396981] RSP: 0018:ffffc900007cfc90 EFLAGS: 00010092
[ 142.398124] RAX: 000000000000008f RBX: ffff88803e9b10a0 RCX: 0000000000000027
[ 142.399605] RDX: ffff88803eba0d08 RSI: 0000000000000001 RDI: ffff88803eba0d00
[ 142.401092] RBP: ffff888007d9a480 R08: ffffffff83b8c808 R09: 0000000000000003
[ 142.402548] R10: ffffffff8348c820 R11: ffffffff83a11d58 R12: ffff888007150000
[ 142.404098] R13: ffff888005961400 R14: ffffffff813221a0 R15: ffff888005961400
[ 142.405561] FS: 0000000000000000(0000) GS:ffff88803eb80000(0000)
knlGS:0000000000000000
[ 142.407297] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 142.408658] CR2: 00007f826bd1a000 CR3: 00000000069db002 CR4: 0000000000772ef0
[ 142.410259] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 142.411871] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 142.413341] PKRU: 55555554
[ 142.414038] Call Trace:
[ 142.414658] <TASK>
[ 142.415249] ? __warn+0x8d/0x180
[ 142.416035] ? check_flush_dependency.part.0+0xad/0x100
[ 142.417182] ? report_bug+0x160/0x170
[ 142.418041] ? handle_bug+0x4f/0x90
[ 142.418861] ? exc_invalid_op+0x14/0x70
[ 142.419853] ? asm_exc_invalid_op+0x16/0x20
[ 142.420877] ? kfree_rcu_shrink_scan+0x120/0x120
[ 142.422029] ? check_flush_dependency.part.0+0xad/0x100
[ 142.423244] __flush_work+0x38a/0x4a0
[ 142.424157] ? find_held_lock+0x2b/0x80
[ 142.425070] ? flush_rcu_work+0x26/0x40
[ 142.425953] ? lock_release+0xb3/0x250
[ 142.426785] ? __mutex_unlock_slowpath+0x2c/0x270
[ 142.427906] flush_rcu_work+0x30/0x40
[ 142.428756] kvfree_rcu_barrier+0xe9/0x130
[ 142.429649] kmem_cache_destroy+0x2b/0x1f0
[ 142.430578] cache_destroy_workfn+0x20/0x40 [slub_kunit]
[ 142.431729] process_one_work+0x1cd/0x560
[ 142.432620] worker_thread+0x183/0x310
[ 142.433487] ? rescuer_thread+0x330/0x330
[ 142.434428] kthread+0xd8/0x1d0
[ 142.435248] ? ret_from_fork+0x17/0x50
[ 142.436165] ? lock_release+0xb3/0x250
[ 142.437106] ? kthreads_online_cpu+0xf0/0xf0
[ 142.438133] ret_from_fork+0x2d/0x50
[ 142.439045] ? kthreads_online_cpu+0xf0/0xf0
[ 142.440428] ret_from_fork_asm+0x11/0x20
[ 142.441476] </TASK>
[ 142.442152] irq event stamp: 22858
[ 142.443002] hardirqs last enabled at (22857): [<ffffffff82044ef4>]
_raw_spin_unlock_irq+0x24/0x30
[ 142.445032] hardirqs last disabled at (22858): [<ffffffff82044ce3>]
_raw_spin_lock_irq+0x43/0x50
[ 142.451450] softirqs last enabled at (22714): [<ffffffff810bfdbc>]
__irq_exit_rcu+0xac/0xd0
[ 142.453345] softirqs last disabled at (22709): [<ffffffff810bfdbc>]
__irq_exit_rcu+0xac/0xd0
[ 142.455305] ---[ end trace 0000000000000000 ]---