On 2025/2/28 7:43, 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 and compaction: >>>> >>>> watchdog: BUG: soft lockup - CPU#30 stuck for 179s! [folio_swap:4714] >>>> Modules linked in: zram xt_MASQUERADE nf_conntrack_netlink nfnetlink iptable_nat xt_addrtype iptable_filter ip_tantel_rapl_msr intel_rapl_common 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 net_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]=SOFTLOCKUP >>>> 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:0000000000000000 >>>> 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: >>>> <IRQ> >>>> ? 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 >>>> </IRQ> >>>> <TASK> >>>> ? 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_test_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 clear why. >>>> >>>> To reproduce the problem, we need firstly a zram device as swap backend, and then run the >>>> reproduction program. The reproduction program consists of three parts: >>>> 1. A process constantly changes the status of shmem large folio by these interfaces: >>>> /sys/kernel/mm/transparent_hugepage/hugepages-<size>/shmem_enabled >>>> 2. A process constantly echo 1 > /proc/sys/vm/compact_memory >>>> 3. A process constantly alloc/free/swapout/swapin shmem large folios. >>>> >>>> I'm not sure whether the first process is necessary but the second and third are. In addition, >>>> I tried hacking to modify compaction_alloc to return NULL, and the problem 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 fixed 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@xxxxxxxxxx/ >>> . >>> >> 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’s patch, shmem folios now use high-order > entry, so the migration code should not update multiple xarray slots. Looks reasonable. I'll try it, thanks. > > Hi Baolin, > > Is your patch affecting anonymous swapping out? If yes, we can remove > the for loop of updating xarray in __folio_migrate_mapping(). > > 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 <linux/sched/sysctl.h> > #include <linux/memory-tiers.h> > #include <linux/pagewalk.h> > +#include <linux/shmem_fs.h> > > #include <asm/tlbflush.h> > > @@ -524,7 +525,11 @@ static int __folio_migrate_mapping(struct address_space *mapping, > folio_set_swapcache(newfolio); > newfolio->private = folio_get_private(folio); > } > - entries = nr; > + /* shmem now uses high-order entry */ > + if (folio->mapping && shmem_mapping(folio->mapping)) > + entries = 1; > + else > + entries = nr; > } else { > VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio); > entries = 1; > > > Best Regards, > Yan, Zi > . >
