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

Uladzislau Rezki
2025-02-25T17:41:25Z

On Tue, Feb 25, 2025 at 10:05:37AM -0700, Keith Busch wrote:
> 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 ]---
Thanks!

I can trigger this also:

<snip>
[ 21.712856] KTAP version 1
[ 21.712862] 1..1
[ 21.714486] KTAP version 1
[ 21.714490] # Subtest: slub_test
[ 21.714492] # module: slub_kunit
[ 21.714495] 1..10
[ 21.750359] ok 1 test_clobber_zone
[ 21.750955] ok 2 test_next_pointer
[ 21.751532] ok 3 test_first_word
[ 21.751991] ok 4 test_clobber_50th_byte
[ 21.752493] ok 5 test_clobber_redzone_free
[ 21.753004] stackdepot: allocating hash table of 1048576 entries via kvcalloc
[ 21.756176] ok 6 test_kmalloc_redzone_access
[ 21.806549] ok 7 test_kfree_rcu
[ 22.058010] ------------[ cut here ]------------
[ 22.058015] workqueue: WQ_MEM_RECLAIM test_kfree_rcu_destroy_wq:cache_destroy_workfn [slub_kunit] is flushing !WQ_MEM_RECLAIM events_unbound:kfree_rcu_work
[ 22.058039] WARNING: CPU: 19 PID: 474 at kernel/workqueue.c:3715 check_flush_dependency.part.0+0xbe/0x130
[ 22.058047] Modules linked in: slub_kunit(E) kunit(E) binfmt_misc(E) bochs(E) drm_client_lib(E) drm_shmem_helper(E) ppdev(E) drm_kms_helper(E) snd_pcm(E) sg(E) snd_timer(E) evdev(E) snd(E) joydev(E) parport_pc(E) parport(E) soundcore(E) serio_raw(E) button(E) pcspkr(E) drm(E) fuse(E) dm_mod(E) efi_pstore(E) configfs(E) loop(E) qemu_fw_cfg(E) ip_tables(E) x_tables(E) autofs4(E) ext4(E) crc16(E) mbcache(E) jbd2(E) sr_mod(E) sd_mod(E) cdrom(E) ata_generic(E) ata_piix(E) libata(E) scsi_mod(E) i2c_piix4(E) psmouse(E) e1000(E) i2c_smbus(E) scsi_common(E) floppy(E)
[ 22.058091] CPU: 19 UID: 0 PID: 474 Comm: kworker/u257:0 Kdump: loaded Tainted: G E N 6.14.0-rc1+ #286
[ 22.058096] Tainted: [E]=UNSIGNED_MODULE, [N]=TEST
[ 22.058097] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[ 22.058099] Workqueue: test_kfree_rcu_destroy_wq cache_destroy_workfn [slub_kunit]
[ 22.058103] RIP: 0010:check_flush_dependency.part.0+0xbe/0x130
[ 22.058106] Code: 75 d0 48 8b 55 18 49 8d 8d c0 00 00 00 4d 89 f0 48 81 c6 c0 00 00 00 48 c7 c7 b0 7d c8 bd c6 05 6c 78 53 01 01 e8 a2 ae fd ff <0f> 0b 5b 5d 41 5c 41 5d 41 5e c3 cc cc cc cc f6 c4 08 74 94 31 ed
[ 22.058108] RSP: 0018:ffff95e5c123fd50 EFLAGS: 00010086
[ 22.058111] RAX: 0000000000000000 RBX: ffff89a4ff22d5a0 RCX: 0000000000000000
[ 22.058113] RDX: 0000000000000003 RSI: ffffffffbdce1697 RDI: 00000000ffffffff
[ 22.058114] RBP: ffff89961043a780 R08: 0000000000000000 R09: 0000000000000003
[ 22.058116] R10: ffff95e5c123fbe8 R11: ffff89a53fefefa8 R12: ffff89960cb6b080
[ 22.058117] R13: ffff899600051400 R14: ffffffffbcf2ba80 R15: ffff89960005a800
[ 22.058120] FS: 0000000000000000(0000) GS:ffff89a4ff2c0000(0000) knlGS:0000000000000000
[ 22.058122] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 22.058124] CR2: 000055bf2cbc6038 CR3: 000000010dc1e000 CR4: 00000000000006f0
[ 22.058128] Call Trace:
[ 22.058130] <TASK>
[ 22.058133] ? __warn+0x85/0x130
[ 22.058137] ? check_flush_dependency.part.0+0xbe/0x130
[ 22.058139] ? report_bug+0x18d/0x1c0
[ 22.058142] ? prb_read_valid+0x17/0x20
[ 22.058147] ? handle_bug+0x58/0x90
[ 22.058151] ? exc_invalid_op+0x13/0x60
[ 22.058154] ? asm_exc_invalid_op+0x16/0x20
[ 22.058158] ? __pfx_kfree_rcu_work+0x10/0x10
[ 22.058162] ? check_flush_dependency.part.0+0xbe/0x130
[ 22.058165] __flush_work+0xd6/0x320
[ 22.058168] flush_rcu_work+0x39/0x50
[ 22.058171] kvfree_rcu_barrier+0xe9/0x130
[ 22.058174] kmem_cache_destroy+0x18/0x140
[ 22.058177] process_one_work+0x184/0x3a0
[ 22.058180] worker_thread+0x24d/0x360
[ 22.058183] ? __pfx_worker_thread+0x10/0x10
[ 22.058185] kthread+0xfc/0x230
[ 22.058189] ? finish_task_switch.isra.0+0x85/0x2a0
[ 22.058192] ? __pfx_kthread+0x10/0x10
[ 22.058195] ret_from_fork+0x30/0x50
[ 22.058199] ? __pfx_kthread+0x10/0x10
[ 22.058202] ret_from_fork_asm+0x1a/0x30
[ 22.058206] </TASK>
[ 22.058207] ---[ end trace 0000000000000000 ]---
[ 23.123507] ok 8 test_kfree_rcu_wq_destroy
[ 23.151033] ok 9 test_leak_destroy
[ 23.151612] ok 10 test_krealloc_redzone_zeroing
[ 23.151617] # slub_test: pass:10 fail:0 skip:0 total:10
[ 23.151619] # Totals: pass:10 fail:0 skip:0 total:10
[ 23.151620] ok 1 slub_test
urezki@pc638:~$
<snip>

but i had to adapt slightly the Vlastimil's test:

diff --git a/lib/slub_kunit.c b/lib/slub_kunit.c
index f11691315c2f..222f6d204b0d 100644
--- a/lib/slub_kunit.c
+++ b/lib/slub_kunit.c
@@ -6,6 +6,7 @@
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/rcupdate.h>
+#include <linux/delay.h>
#include "../mm/slab.h"

static struct kunit_resource resource;
@@ -181,6 +182,63 @@ static void test_kfree_rcu(struct kunit *test)
KUNIT_EXPECT_EQ(test, 0, slab_errors);
}

+struct cache_destroy_work {
+ struct work_struct work;
+ struct kmem_cache *s;
+};
+
+static void cache_destroy_workfn(struct work_struct *w)
+{
+ struct cache_destroy_work *cdw;
+
+ cdw = container_of(w, struct cache_destroy_work, work);
+ kmem_cache_destroy(cdw->s);
+}
+
+#define KMEM_CACHE_DESTROY_NR 10
+
+static void test_kfree_rcu_wq_destroy(struct kunit *test)
+{
+ struct test_kfree_rcu_struct *p;
+ struct cache_destroy_work cdw;
+ struct workqueue_struct *wq;
+ struct kmem_cache *s;
+ unsigned int rnd;
+ int i;
+
+ if (IS_BUILTIN(CONFIG_SLUB_KUNIT_TEST))
+ kunit_skip(test, "can't do kfree_rcu() when test is built-in");
+
+ INIT_WORK_ONSTACK(&cdw.work, cache_destroy_workfn);
+ wq = alloc_workqueue("test_kfree_rcu_destroy_wq",
+ WQ_HIGHPRI | WQ_UNBOUND | WQ_MEM_RECLAIM, 0);
+
+ if (!wq)
+ kunit_skip(test, "failed to alloc wq");
+
+ for (i = 0; i < KMEM_CACHE_DESTROY_NR; i++) {
+ s = test_kmem_cache_create("TestSlub_kfree_rcu_wq_destroy",
+ sizeof(struct test_kfree_rcu_struct),
+ SLAB_NO_MERGE);
+
+ if (!s)
+ kunit_skip(test, "failed to create cache");
+
+ rnd = get_random_u8() % 255;
+ p = kmem_cache_alloc(s, GFP_KERNEL);
+ kfree_rcu(p, rcu);
+
+ cdw.s = s;
+
+ msleep(rnd);
+ queue_work(wq, &cdw.work);
+ flush_work(&cdw.work);
+ }
+
+ destroy_workqueue(wq);
+ KUNIT_EXPECT_EQ(test, 0, slab_errors);
+}
+
static void test_leak_destroy(struct kunit *test)
{
struct kmem_cache *s = test_kmem_cache_create("TestSlub_leak_destroy",
@@ -254,6 +312,7 @@ static struct kunit_case test_cases[] = {
KUNIT_CASE(test_clobber_redzone_free),
KUNIT_CASE(test_kmalloc_redzone_access),
KUNIT_CASE(test_kfree_rcu),
+ KUNIT_CASE(test_kfree_rcu_wq_destroy),
KUNIT_CASE(test_leak_destroy),
KUNIT_CASE(test_krealloc_redzone_zeroing),
{}

--
Uladzislau Rezki