Message-ID: <20251028211533.47694-1-luizcap@redhat.com>
Date: Tue, 28 Oct 2025 17:15:33 -0400
From: Luiz Capitulino <luizcap@...hat.com>
To: hca@...ux.ibm.com,
	borntraeger@...ux.ibm.com,
	joao.m.martins@...cle.com,
	mike.kravetz@...cle.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-s390@...r.kernel.org,
	gor@...ux.ibm.com,
	gerald.schaefer@...ux.ibm.com,
	agordeev@...ux.ibm.com
Cc: osalvador@...e.de,
	akpm@...ux-foundation.org,
	david@...hat.com,
	aneesh.kumar@...nel.org
Subject: [PATCH v2] s390: fix HugeTLB vmemmap optimization crash

A reproducible crash occurs when enabling HugeTLB vmemmap optimization (HVO)
on s390. The crash and the proposed fix were worked on an s390 KVM guest
running on an older hypervisor, as I don't have access to an LPAR. However,
the same issue should occur on bare-metal.

Reproducer (it may take a few runs to trigger):

 # sysctl vm.hugetlb_optimize_vmemmap=1
 # echo 1 > /proc/sys/vm/nr_hugepages
 # echo 0 > /proc/sys/vm/nr_hugepages

Crash log:

[   52.340369] list_del corruption. prev->next should be 000000d382110008, but was 000000d7116d3880. (prev=000000d7116d3910)
[   52.340420] ------------[ cut here ]------------
[   52.340424] kernel BUG at lib/list_debug.c:62!
[   52.340566] monitor event: 0040 ilc:2 [#1]SMP
[   52.340573] Modules linked in: ctcm fsm qeth ccwgroup zfcp scsi_transport_fc qdio dasd_fba_mod dasd_eckd_mod dasd_mod xfs ghash_s390 prng des_s390 libdes sha3_512_s390 sha3_256_s390 virtio_net virtio_blk net_failover sha_common failover dm_mirror dm_region_hash dm_log dm_mod paes_s390 crypto_engine pkey_cca pkey_ep11 zcrypt pkey_pckmo pkey aes_s390
[   52.340606] CPU: 1 UID: 0 PID: 1672 Comm: root-rep2 Kdump: loaded Not tainted 6.18.0-rc3 #1 NONE
[   52.340610] Hardware name: IBM 3931 LA1 400 (KVM/Linux)
[   52.340611] Krnl PSW : 0704c00180000000 0000015710cda7fe (__list_del_entry_valid_or_report+0xfe/0x128)
[   52.340619]            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3
[   52.340622] Krnl GPRS: c0000000ffffefff 0000000100000027 000000000000006d 0000000000000000
[   52.340623]            000000d7116d35d8 000000d7116d35d0 0000000000000002 000000d7116d39b0
[   52.340625]            000000d7116d3880 000000d7116d3910 000000d7116d3910 000000d382110008
[   52.340626]            000003ffac1ccd08 000000d7116d39b0 0000015710cda7fa 000000d7116d37d0
[   52.340632] Krnl Code: 0000015710cda7ee: c020003e496f	larl	%r2,00000157114a3acc
           0000015710cda7f4: c0e5ffd5280e	brasl	%r14,000001571077f810
          #0000015710cda7fa: af000000		mc	0,0
          >0000015710cda7fe: b9040029		lgr	%r2,%r9
           0000015710cda802: c0e5ffe5e193	brasl	%r14,0000015710996b28
           0000015710cda808: e34090080004	lg	%r4,8(%r9)
           0000015710cda80e: b9040059		lgr	%r5,%r9
           0000015710cda812: b9040038		lgr	%r3,%r8
[   52.340643] Call Trace:
[   52.340645]  [<0000015710cda7fe>] __list_del_entry_valid_or_report+0xfe/0x128
[   52.340649] ([<0000015710cda7fa>] __list_del_entry_valid_or_report+0xfa/0x128)
[   52.340652]  [<0000015710a30b2e>] hugetlb_vmemmap_restore_folios+0x96/0x138
[   52.340655]  [<0000015710a268ac>] update_and_free_pages_bulk+0x64/0x150
[   52.340659]  [<0000015710a26f8a>] set_max_huge_pages+0x4ca/0x6f0
[   52.340662]  [<0000015710a273ba>] hugetlb_sysctl_handler_common+0xea/0x120
[   52.340665]  [<0000015710a27484>] hugetlb_sysctl_handler+0x44/0x50
[   52.340667]  [<0000015710b53ffa>] proc_sys_call_handler+0x17a/0x280
[   52.340672]  [<0000015710a90968>] vfs_write+0x2c8/0x3a0
[   52.340676]  [<0000015710a90bd2>] ksys_write+0x72/0x100
[   52.340679]  [<00000157111483a8>] __do_syscall+0x150/0x318
[   52.340682]  [<0000015711153a5e>] system_call+0x6e/0x90
[   52.340684] Last Breaking-Event-Address:
[   52.340684]  [<000001571077f85c>] _printk+0x4c/0x58
[   52.340690] Kernel panic - not syncing: Fatal exception: panic_on_oops

This issue was introduced by commit f13b83fdd996 ("hugetlb: batch TLB
flushes when freeing vmemmap"). Before that change, the HVO
implementation called flush_tlb_kernel_range() each time a vmemmap
PMD split and remapping was performed. The mentioned commit changed this
to issue a few flush_tlb_all() calls after performing all remappings.

However, on s390, flush_tlb_kernel_range() expands to
__tlb_flush_kernel() while flush_tlb_all() is not implemented. As a
result, we went from flushing the TLB for every remapping to no flushing
at all.

This commit fixes this by implementing flush_tlb_all() on s390 as an
alias to __tlb_flush_global(). This should cause a flush on all TLB
entries on all CPUs as expected by the flush_tlb_all() semantics.

Fixes: f13b83fdd996 ("hugetlb: batch TLB flushes when freeing vmemmap")
Signed-off-by: Luiz Capitulino <luizcap@...hat.com>
---
 arch/s390/include/asm/tlbflush.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/s390/include/asm/tlbflush.h b/arch/s390/include/asm/tlbflush.h
index 75491baa21974..0d53993534840 100644
--- a/arch/s390/include/asm/tlbflush.h
+++ b/arch/s390/include/asm/tlbflush.h
@@ -103,9 +103,13 @@ static inline void __tlb_flush_mm_lazy(struct mm_struct * mm)
  * flush_tlb_range functions need to do the flush.
  */
 #define flush_tlb()				do { } while (0)
-#define flush_tlb_all()				do { } while (0)
 #define flush_tlb_page(vma, addr)		do { } while (0)
 
+static inline void flush_tlb_all(void)
+{
+	__tlb_flush_global();
+}
+
 static inline void flush_tlb_mm(struct mm_struct *mm)
 {
 	__tlb_flush_mm_lazy(mm);
-- 
2.51.0

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