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1zGNyJ4OE9ZpBtFxvX4RSVtlPStPUrTQU1tilYzO0rgzBRAwycmMQlqBjR+c1q1fkgAT/XTbQU+Po44UJT5ki6HqNdhHjCjiS0HG8j+gnqvYnL6AZCh1RaEBt0JIpep3e6L6yghbTNQxNnbe13w8Dpun9CCrb0T4+g/yrCOQA5FwCJBLn9NC2KoHdClnFeyhaoJvxD/c/Mu4IQauCvg/ZZggfb+l7sc3/IGpwzN+7iZ29SeyRkjAYb8w8DcWQ43RWzRVYz/UpS1r/8ZyEv8tWSn8CgI5zY5jV8PhIY4G25WZfbSN1P2b1zNXiDtU65esDODGiODuukh2tNqGCdIIyN+vr+uvTe98U9K+YiXeivSHZIpucJTG/ouFhap8HmUop5k8IAnyNbLB37G7i2ItmDLHB/jAEn9sYKc0SYTdnVUUVEXE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 27 Feb 2025, at 22:39, Baolin Wang wrote: > On 2025/2/28 07:43, Zi Yan wrote: >> On 27 Feb 2025, at 2:04, Liu Shixin wrote: >> >>> On 2025/2/26 15:22, Baolin Wang wrote: >>>> Add Zi. >>>> >>>> On 2025/2/26 15:03, Liu Shixin wrote: >>>>> Hi all, >>>>> >>>>> I found a softlockup when testing shmem large folio swapout-swapin an= d compaction: >>>>> >>>>> watchdog: BUG: soft lockup - CPU#30 stuck for 179s! [folio_swap:47= 14] >>>>> Modules linked in: zram xt_MASQUERADE nf_conntrack_netlink nfnetli= nk iptable_nat xt_addrtype iptable_filter ip_tantel_rapl_msr intel_rapl_com= mon intel_uncore_frequency_common skx_edac_common nfit libnvdimm kvm_intel = kvm rapl cixt4 mbcache jbd2 sr_mod cdrom ata_generic ata_piix virtio_net ne= t_failover ghash_clmulni_intel libata sha512_ssse3 >>>>> CPU: 30 UID: 0 PID: 4714 Comm: folio_swap Kdump: loaded Tainted: G= L 6.14.0-rc4-next-20250225+ #2 >>>>> Tainted: [L]=3DSOFTLOCKUP >>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0= -1ubuntu1.1 04/01/2014 >>>>> RIP: 0010:xas_load+0x5d/0xc0 >>>>> Code: 08 48 d3 ea 83 e2 3f 89 d0 48 83 c0 04 48 8b 44 c6 08 48 89 = 73 18 48 89 c1 83 e1 03 48 83 f9 02 75 08 48 3d >>>>> RSP: 0000:ffffadf142f1ba60 EFLAGS: 00000293 >>>>> RAX: ffffe524cc4f6700 RBX: ffffadf142f1ba90 RCX: 0000000000000000 >>>>> RDX: 0000000000000011 RSI: ffff9a3e058acb68 RDI: ffffadf142f1ba90 >>>>> RBP: fffffffffffffffe R08: ffffadf142f1bb50 R09: 0000000000000392 >>>>> R10: 0000000000000001 R11: 0000000000000000 R12: 0000000000000011 >>>>> R13: ffffadf142f1bb48 R14: ffff9a3e04e9c588 R15: 0000000000000000 >>>>> FS: 00007fd957666740(0000) GS:ffff9a41ac0e5000(0000) knlGS:000000= 0000000000 >>>>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>>>> CR2: 00007fd922860000 CR3: 000000025c360001 CR4: 0000000000772ef0 >>>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >>>>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >>>>> PKRU: 55555554 >>>>> Call Trace: >>>>> >>>>> ? watchdog_timer_fn+0x1c9/0x250 >>>>> ? __pfx_watchdog_timer_fn+0x10/0x10 >>>>> ? __hrtimer_run_queues+0x10e/0x250 >>>>> ? hrtimer_interrupt+0xfb/0x240 >>>>> ? __sysvec_apic_timer_interrupt+0x4e/0xe0 >>>>> ? sysvec_apic_timer_interrupt+0x68/0x90 >>>>> >>>>> >>>>> ? asm_sysvec_apic_timer_interrupt+0x16/0x20 >>>>> ? xas_load+0x5d/0xc0 >>>>> xas_find+0x153/0x1a0 >>>>> find_get_entries+0x73/0x280 >>>>> shmem_undo_range+0x1fc/0x640 >>>>> shmem_evict_inode+0x109/0x270 >>>>> evict+0x107/0x240 >>>>> ? fsnotify_destroy_marks+0x25/0x180 >>>>> ? _atomic_dec_and_lock+0x35/0x50 >>>>> __dentry_kill+0x71/0x190 >>>>> dput+0xd1/0x190 >>>>> __fput+0x128/0x2a0 >>>>> task_work_run+0x57/0x90 >>>>> syscall_exit_to_user_mode+0x1cb/0x1e0 >>>>> do_syscall_64+0x67/0x170 >>>>> entry_SYSCALL_64_after_hwframe+0x76/0x7e >>>>> RIP: 0033:0x7fd95776eb8b >>>>> >>>>> If CONFIG_DEBUG_VM is enabled, we will meet VM_BUG_ON_FOLIO(!folio_te= st_locked(folio)) in >>>>> shmem_add_to_page_cache() too. It seems that the problem is related = to memory migration or >>>>> compaction which is necessary for reproduction, although without a c= lear why. >>>>> >>>>> To reproduce the problem, we need firstly a zram device as swap backe= nd, and then run the >>>>> reproduction program. The reproduction program consists of three part= s: >>>>> 1. A process constantly changes the status of shmem large folio by= these interfaces: >>>>> /sys/kernel/mm/transparent_hugepage/hugepages-/shmem_= enabled >>>>> 2. A process constantly echo 1 > /proc/sys/vm/compact_memory >>>>> 3. A process constantly alloc/free/swapout/swapin shmem large foli= os. >>>>> >>>>> I'm not sure whether the first process is necessary but the second an= d third are. In addition, >>>>> I tried hacking to modify compaction_alloc to return NULL, and the pr= oblem disappeared, >>>>> so I guess the problem is in migration. >>>>> >>>>> The problem is different with https://lore.kernel.org/all/1738717785.= im3r5g2vxc.none@localhost/ >>>>> since I have confirmed this porblem still existed after merge the fix= ed patch. >>>> >>>> Could you check if your version includes Zi's fix[1]? Not sure if it's= related to the shmem large folio split. >>>> >>>> [1] https://lore.kernel.org/all/AF487A7A-F685-485D-8D74-756C843D6F0A@n= vidia.com/ >>>> . >>>> >>> Already include this patch when test. >> >> Hi Shixin, >> >> Can you try the diff below? It fixed my local repro. >> >> The issue is that after Baolin=E2=80=99s patch, shmem folios now use hig= h-order >> entry, so the migration code should not update multiple xarray slots. > > It is not after my patches. After converting shmem to use folio, shmem ma= pping will store large order, but during swap, the shmem large folio will b= e split (whereas my patches allow shmem large folio swap without splitting)= . Got it. Sorry for pointing the wrong source. > >> Hi Baolin, >> >> Is your patch affecting anonymous swapping out? If yes, we can remove > > No. > >> the for loop of updating xarray in __folio_migrate_mapping(). > > I think the issue is introduced by commit fc346d0a70a1 ("mm: migrate high= -order folios in swap cache correctly"), which did not handle shmem folio c= orrectly. I agree. What a mess. So right now only swap cache used by anonymous memory does not use multi-index entry. > >> diff --git a/mm/migrate.c b/mm/migrate.c >> index 365c6daa8d1b..be77932596b3 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -44,6 +44,7 @@ >> #include >> #include >> #include >> +#include >> >> #include >> >> @@ -524,7 +525,11 @@ static int __folio_migrate_mapping(struct address_s= pace *mapping, >> folio_set_swapcache(newfolio); >> newfolio->private =3D folio_get_private(folio); >> } >> - entries =3D nr; >> + /* shmem now uses high-order entry */ >> + if (folio->mapping && shmem_mapping(folio->mapping)) > > Nit: we've already checked the 'mapping', and we can simplify it to 'shme= m_mapping(mapping)'. Sure. > >> + entries =3D 1; >> + else >> + entries =3D nr; >> } else { >> VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio); >> entries =3D 1; > > Good catch. The fix look good to me. Thanks. Thank you for checking the patch. I will send a proper one out. Best Regards, Yan, Zi