Re: [PATCH v5] mm/rmap: do not add fully unmapped large folio to deferred split list

[Zi Yan]

On 1 May 2024, at 9:24, Alexander Gordeev wrote:

> On Fri, Apr 26, 2024 at 03:02:53PM -0400, Zi Yan wrote:
>
> Hi Zi,
>
> It increasingly looks like this commit is crashing on s390 since
> 2024-04-30 in linux-next. If I do not miss something - since it
> was included in mm-everything.
>
>> @@ -1553,9 +1558,10 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
>>  		 * page of the folio is unmapped and at least one page
>>  		 * is still mapped.
>>  		 */
>> -		if (folio_test_large(folio) && folio_test_anon(folio))
>> -			if (level == RMAP_LEVEL_PTE || nr < nr_pmdmapped)
>> -				deferred_split_folio(folio);
>> +		if (folio_test_anon(folio) &&
>> +		    list_empty(&folio->_deferred_list) &&
>
> An attempt to reference folio->_deferred_list causes the crash below.

So if you remove this line, the crash no longer happens? It looks strange to
me that referencing a anonymous folio's _deferred_list would cause a crash.
Hmm, unless the folio is order-0.

Can you try the patch below and see if it fixes the crash? It moves partially_mapped
ahead to exclude order-0 folios.

diff --git a/mm/rmap.c b/mm/rmap.c
index 087a79f1f611..2d27c92bb6d5 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1557,9 +1557,8 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
                 * page of the folio is unmapped and at least one page
                 * is still mapped.
                 */
-               if (folio_test_anon(folio) &&
-                   list_empty(&folio->_deferred_list) &&
-                   partially_mapped)
+               if (folio_test_anon(folio) && partially_mapped &&
+                   list_empty(&folio->_deferred_list))
                        deferred_split_folio(folio);
        }


>
>> +		    partially_mapped)
>> +			deferred_split_folio(folio);
>>  	}
>>
>>  	/*
>
> [  507.227423] Unable to handle kernel pointer dereference in virtual kernel address space
> [  507.227432] Failing address: 000001d689000000 TEID: 000001d689000803
> [  507.227435] Fault in home space mode while using kernel ASCE.
> [  507.227439] AS:0000000180788007 R3:00000001fe2cc007 S:0000000000000020
> [  507.227492] Oops: 0010 ilc:3 [#1] SMP
> [  507.227497] Modules linked in: vmur(E) kvm(E) algif_hash(E) af_alg(E) binfmt_misc(E) nft_fib_inet(E) nft_fib_ipv4(E) nft_fib_ipv6(E) nft_fib(E) nft_reject_inet(E) nf_reject_ipv4(E) nf_reject_ipv6(E) nft_reject(E) nft_ct(E) nft_chain_nat(E) nf_nat(E) nf_conntrack(E) nf_defrag_ipv6(E) nf_defrag_ipv4(E) ip_set(E) nf_tables(E) nfnetlink(E) dm_service_time(E) s390_trng(E) vfio_ccw(E) mdev(E) vfio_iommu_type1(E) vfio(E) sch_fq_codel(E) loop(E) configfs(E) lcs(E) ctcm(E) fsm(E) zfcp(E) scsi_transport_fc(E) ghash_s390(E) prng(E) chacha_s390(E) libchacha(E) aes_s390(E) des_s390(E) libdes(E) sha3_512_s390(E) sha3_256_s390(E) sha512_s390(E) sha256_s390(E) sha1_s390(E) sha_common(E) scsi_dh_rdac(E) scsi_dh_emc(E) scsi_dh_alua(E) pkey(E) zcrypt(E) rng_core(E) dm_multipath(E) autofs4(E)
> [  507.227546] Unloaded tainted modules: dcssblk(E):2 [last unloaded: dcssblk(E)]
> [  507.230569] CPU: 0 PID: 36783 Comm: pahole Tainted: G            E      6.9.0-20240430.rc6.git237.d04466706db5.300.fc39.s390x+next #1
> [  507.230574] Hardware name: IBM 3931 A01 703 (z/VM 7.3.0)
> [  507.230576] Krnl PSW : 0704f00180000000 0000025e1092a430 (folio_remove_rmap_ptes+0xe0/0x140)
> [  507.230588]            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:3 PM:0 RI:0 EA:3
> [  507.230592] Krnl GPRS: ffffffffffffe377 0000000000000000 0000025e122075b8 0000000000000000
> [  507.230595]            ffffffffffffffff 0000025d8f613288 8800000000000000 00000157a38b8700
> [  507.230598]            000000023fffe13f 0000000000000000 000001579ccd75c0 000001d688ffff80
> [  507.230602]            000003ffb9cacf98 000001d688ffff80 0000025e1092a428 000001de11fab878
> [  507.230610] Krnl Code: 0000025e1092a422: c0e500039f47        brasl   %r14,0000025e1099e2b0
> [  507.230610]            0000025e1092a428: 9101b01f            tm      31(%r11),1
> [  507.230610]           #0000025e1092a42c: a784ffb9            brc     8,0000025e1092a39e
> [  507.230610]           >0000025e1092a430: e340b0900004        lg      %r4,144(%r11)
> [  507.230610]            0000025e1092a436: 4150b090            la      %r5,144(%r11)
> [  507.230610]            0000025e1092a43a: ec45ffb26064        cgrj    %r4,%r5,6,0000025e1092a39e
> [  507.230610]            0000025e1092a440: a7910001            tmll    %r9,1
> [  507.230610]            0000025e1092a444: a784ffad            brc     8,0000025e1092a39e
> [  507.230672] Call Trace:
> [  507.230678]  [<0000025e1092a430>] folio_remove_rmap_ptes+0xe0/0x140
> [  507.230682] ([<0000025e1092a428>] folio_remove_rmap_ptes+0xd8/0x140)
> [  507.230685]  [<0000025e1090d76a>] zap_present_ptes.isra.0+0x222/0x918
> [  507.230689]  [<0000025e1090e008>] zap_pte_range+0x1a8/0x4e8
> [  507.230692]  [<0000025e1090e58c>] zap_p4d_range+0x244/0x480
> [  507.230695]  [<0000025e1090eb22>] unmap_page_range+0xea/0x2c0
> [  507.230698]  [<0000025e1090ed92>] unmap_single_vma.isra.0+0x9a/0xf0
> [  507.230701]  [<0000025e1090ee9e>] unmap_vmas+0xb6/0x1a0
> [  507.230705]  [<0000025e1091e0d4>] exit_mmap+0xc4/0x3d0
> [  507.230709]  [<0000025e10675c64>] __mmput+0x54/0x150
> [  507.230714]  [<0000025e1067f3ba>] exit_mm+0xca/0x138
> [  507.230717]  [<0000025e1067f690>] do_exit+0x268/0x520
> [  507.230721]  [<0000025e1067fb38>] do_group_exit+0x40/0xb8
> [  507.230725]  [<0000025e1067fc0e>] __s390x_sys_exit_group+0x2e/0x30
> [  507.230729]  [<0000025e1136ba4e>] __do_syscall+0x216/0x2d0
> [  507.230736]  [<0000025e1137c848>] system_call+0x70/0x98
> [  507.230780] Last Breaking-Event-Address:
> [  507.230783]  [<0000025e1099e32a>] __lruvec_stat_mod_folio+0x7a/0xb0
> [  507.230789] Kernel panic - not syncing: Fatal exception: panic_on_oops
> 00: HCPGIR450W CP entered; disabled wait PSW 00020001 80000000 0000025E 10630B56
>
> Thanks!

--
Best Regards,
Yan, Zi

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