net/smc is calling proto_register(&smc_proto, 1) with smc_proto.slab_flags = SLAB_TYPESAFE_BY_RCU.
Right after the last SMC socket is destroyed, proto_unregister(&smc_proto) is called, which
calls kmem_cache_destroy(prot->slab). This results in a kernel crash in __free_slab().
Platform is s390x, reproduced on kernel 5.4-rc1. The problem was introduced by commit
fb2f2b0adb98 ("mm: memcg/slab: reparent memcg kmem_caches on cgroup removal")
I added a 'call graph', below of that is the crash log and a (simple) patch that works for me,
but I don't know if this is the correct way to fix it.
(Please keep me on CC of this thread because I do not follow the mm mailing list, thank you)
kmem_cache_destroy()
-> shutdown_memcg_caches()
-> shutdown_cache()
-> __kmem_cache_shutdown() (slub.c)
-> free_partial()
-> discard_slab()
-> free_slab() -- call to __free_slab() is delayed
-> call_rcu(rcu_free_slab)
-> memcg_unlink_cache()
-> WRITE_ONCE(s->memcg_params.memcg, NULL); -- !!!
-> list_add_tail(&s->list, &slab_caches_to_rcu_destroy);
-> schedule_work(&slab_caches_to_rcu_destroy_work); -> work_fn uses rcu_barrier() to wait for rcu_batch,
so work_fn is not further involved here...
... rcu grace period ...
rcu_batch()
...
-> rcu_free_slab() (slub.c)
-> __free_slab()
-> uncharge_slab_page()
-> memcg_uncharge_slab()
-> memcg = READ_ONCE(s->memcg_params.memcg); -- !!! memcg == NULL
-> mem_cgroup_lruvec(memcg)
-> mz = mem_cgroup_nodeinfo(memcg, pgdat->node_id); -- mz == NULL
-> lruvec = &mz->lruvec; -- lruvec == NULL
-> lruvec->pgdat = pgdat; -- *crash*
The crash log:
349.361168¨ Unable to handle kernel pointer dereference in virtual kernel address space
349.361210¨ Failing address: 0000000000000000 TEID: 0000000000000483
349.361223¨ Fault in home space mode while using kernel ASCE.
349.361240¨ AS:00000000017d4007 R3:000000007fbd0007 S:000000007fbff000 P:000000000000003d
349.361340¨ Oops: 0004 ilc:3 Ý#1¨ PREEMPT SMP
349.361349¨ Modules linked in: tcp_diag inet_diag xt_tcpudp ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ip6table_nat ip6table_mangle ip6table_raw ip6table_security iptable_at nf_nat iptable_mangle iptable_raw iptable_security nf_conntrack nf_defrag_ipv6 nf_de
349.361436¨ CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.3.0-05872-g6133e3e4bada-dirty #14
349.361445¨ Hardware name: IBM 2964 NC9 702 (z/VM 6.4.0)
349.361450¨ Krnl PSW : 0704d00180000000 00000000003cadb6 (__free_slab+0x686/0x6b0)
349.361464¨ R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 RI:0 EA:3
349.361470¨ Krnl GPRS: 00000000f3a32928 0000000000000000 000000007fbf5d00 000000000117c4b8
349.361475¨ 0000000000000000 000000009e3291c1 0000000000000000 0000000000000000
349.361481¨ 0000000000000003 0000000000000008 000000002b478b00 000003d080a97600
349.361481¨ 0000000000000003 0000000000000008 000000002b478b00 000003d080a97600
349.361486¨ 000000000117ba00 000003e000057db0 00000000003cabcc 000003e000057c78
349.361500¨ Krnl Code: 00000000003cada6: e310a1400004 lg %r1,320(%r10)
349.361500¨ 00000000003cadac: c0e50046c286 brasl %r14,ca32b8
349.361500¨ #00000000003cadb2: a7f4fe36 brc 15,3caa1e
349.361500¨ >00000000003cadb6: e32060800024 stg %r2,128(%r6)
349.361500¨ 00000000003cadbc: a7f4fd9e brc 15,3ca8f8
349.361500¨ 00000000003cadc0: c0e50046790c brasl %r14,c99fd8
349.361500¨ 00000000003cadc6: a7f4fe2c brc 15,3caa
349.361500¨ 00000000003cadc6: a7f4fe2c brc 15,3caa1e
349.361500¨ 00000000003cadca: ecb1ffff00d9 aghik %r11,%r1,-1
349.361619¨ Call Trace:
349.361627¨ (Ý<00000000003cabcc>¨ __free_slab+0x49c/0x6b0)
349.361634¨ Ý<00000000001f5886>¨ rcu_core+0x5a6/0x7e0
349.361643¨ Ý<0000000000ca2dea>¨ __do_softirq+0xf2/0x5c0
349.361652¨ Ý<0000000000152644>¨ irq_exit+0x104/0x130
349.361659¨ Ý<000000000010d222>¨ do_IRQ+0x9a/0xf0
349.361667¨ Ý<0000000000ca2344>¨ ext_int_handler+0x130/0x134
349.361674¨ Ý<0000000000103648>¨ enabled_wait+0x58/0x128
349.361681¨ (Ý<0000000000103634>¨ enabled_wait+0x44/0x128)
349.361688¨ Ý<0000000000103b00>¨ arch_cpu_idle+0x40/0x58
349.361695¨ Ý<0000000000ca0544>¨ default_idle_call+0x3c/0x68
349.361704¨ Ý<000000000018eaa4>¨ do_idle+0xec/0x1c0
349.361748¨ Ý<000000000018ee0e>¨ cpu_startup_entry+0x36/0x40
349.361756¨ Ý<000000000122df34>¨ arch_call_rest_init+0x5c/0x88
349.361761¨ Ý<0000000000000000>¨ 0x0
349.361765¨ INFO: lockdep is turned off.
349.361769¨ Last Breaking-Event-Address:
349.361774¨ Ý<00000000003ca8f4>¨ __free_slab+0x1c4/0x6b0
349.361781¨ Kernel panic - not syncing: Fatal exception in interrupt
A fix that works for me (RFC):
diff --git a/mm/slab.h b/mm/slab.h
index a62372d0f271..b19a3f940338 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -328,7 +328,7 @@ static __always_inline void memcg_uncharge_slab(struct page *page, int order,
rcu_read_lock();
memcg = READ_ONCE(s->memcg_params.memcg);
- if (likely(!mem_cgroup_is_root(memcg))) {
+ if (likely(memcg && !mem_cgroup_is_root(memcg))) {
lruvec = mem_cgroup_lruvec(page_pgdat(page), memcg);
mod_lruvec_state(lruvec, cache_vmstat_idx(s), -(1 << order));
memcg_kmem_uncharge_memcg(page, order, memcg);
--
Karsten
(I'm a dude)
