Re: CPU lockup in or near new filecache code

Chuck Lever
2019-12-18T23:21:12Z

> On Dec 13, 2019, at 3:12 PM, Trond Myklebust <trondmy@hammerspace.com> wrote:
>
> On Wed, 2019-12-11 at 15:01 -0500, Chuck Lever wrote:
>> OK, I finally got a hit. It took a long time. I've seen this
>> particular
>> stack trace before, several times.
>>
>> Dec 11 14:58:34 klimt kernel: watchdog: BUG: soft lockup - CPU#0
>> stuck for 22s! [nfsd:2005]
>> Dec 11 14:58:34 klimt kernel: Modules linked in: rpcsec_gss_krb5
>> ocfs2_dlmfs ocfs2_stack_o2cb ocfs2_dlm ocfs2_nodemanager
>> ocfs2_stackglue ib_umad ib_ipoib mlx4_ib sb_edac x86_pkg_temp_thermal
>> kvm_intel coretemp kvm irqbypass crct10dif_pclmul crc32_pclmul
>> ghash_clmulni_intel iTCO_wdt ext4 iTCO_vendor_support aesni_intel
>> mbcache jbd2 glue_helper rpcrdma crypto_simd cryptd rdma_ucm ib_iser
>> rdma_cm pcspkr iw_cm ib_cm mei_me raid0 libiscsi lpc_ich mei sg
>> scsi_transport_iscsi i2c_i801 mfd_core wmi ipmi_si ipmi_devintf
>> ipmi_msghandler ioatdma acpi_power_meter nfsd nfs_acl lockd
>> auth_rpcgss grace sunrpc ip_tables xfs libcrc32c mlx4_en sr_mod
>> sd_mod cdrom qedr ast drm_vram_helper drm_ttm_helper ttm crc32c_intel
>> drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops drm igb
>> dca i2c_algo_bit i2c_core mlx4_core ahci libahci libata nvme
>> nvme_core qede qed dm_mirror dm_region_hash dm_log dm_mod crc8
>> ib_uverbs dax ib_core
>> Dec 11 14:58:34 klimt kernel: CPU: 0 PID: 2005 Comm: nfsd Tainted:
>> G W 5.5.0-rc1-00003-g170e7adc2317 #1401
>> Dec 11 14:58:34 klimt kernel: Hardware name: Supermicro Super
>> Server/X10SRL-F, BIOS 1.0c 09/09/2015
>> Dec 11 14:58:34 klimt kernel: RIP: 0010:__srcu_read_lock+0x23/0x24
>> Dec 11 14:58:34 klimt kernel: Code: 07 00 0f 1f 40 00 c3 0f 1f 44 00
>> 00 8b 87 c8 c3 00 00 48 8b 97 f0 c3 00 00 83 e0 01 48 63 c8 65 48 ff
>> 04 ca f0 83 44 24 fc 00 <c3> 0f 1f 44 00 00 f0 83 44 24 fc 00 48 63
>> f6 48 8b 87 f0 c3 00 00
>> Dec 11 14:58:34 klimt kernel: RSP: 0018:ffffc90001d97bd0 EFLAGS:
>> 00000246 ORIG_RAX: ffffffffffffff13
>> Dec 11 14:58:34 klimt kernel: RAX: 0000000000000001 RBX:
>> ffff888830d0eb78 RCX: 0000000000000001
>> Dec 11 14:58:34 klimt kernel: RDX: 0000000000030f00 RSI:
>> ffff888853f4da00 RDI: ffffffff82815a40
>> Dec 11 14:58:34 klimt kernel: RBP: ffff88883112d828 R08:
>> ffff888843540000 R09: ffffffff8121d707
>> Dec 11 14:58:34 klimt kernel: R10: ffffc90001d97bf0 R11:
>> 0000000000001b84 R12: ffff888853f4da00
>> Dec 11 14:58:34 klimt kernel: R13: ffff8888132a1410 R14:
>> ffff88883112d7e0 R15: 00000000ffffffef
>> Dec 11 14:58:34 klimt kernel: FS: 0000000000000000(0000)
>> GS:ffff88885fc00000(0000) knlGS:0000000000000000
>> Dec 11 14:58:34 klimt kernel: CS: 0010 DS: 0000 ES: 0000 CR0:
>> 0000000080050033
>> Dec 11 14:58:34 klimt kernel: CR2: 00007f2d6a2d8000 CR3:
>> 0000000859b38004 CR4: 00000000001606f0
>> Dec 11 14:58:34 klimt kernel: Call Trace:
>> Dec 11 14:58:34 klimt kernel: fsnotify_grab_connector+0x16/0x4f
>> Dec 11 14:58:34 klimt kernel: fsnotify_find_mark+0x11/0x6a
>> Dec 11 14:58:34 klimt kernel: nfsd_file_acquire+0x3a9/0x5b2 [nfsd]
>> Dec 11 14:58:34 klimt kernel: nfs4_get_vfs_file+0x14c/0x20f [nfsd]
>> Dec 11 14:58:34 klimt kernel: nfsd4_process_open2+0xcd6/0xd98 [nfsd]
>> Dec 11 14:58:34 klimt kernel: ? fh_verify+0x42e/0x4ef [nfsd]
>> Dec 11 14:58:34 klimt kernel: ? nfsd4_process_open1+0x233/0x29d
>> [nfsd]
>> Dec 11 14:58:34 klimt kernel: nfsd4_open+0x500/0x5cb [nfsd]
>> Dec 11 14:58:34 klimt kernel: nfsd4_proc_compound+0x32a/0x5c7 [nfsd]
>> Dec 11 14:58:34 klimt kernel: nfsd_dispatch+0x102/0x1e2 [nfsd]
>> Dec 11 14:58:34 klimt kernel: svc_process_common+0x3b3/0x65d [sunrpc]
>> Dec 11 14:58:34 klimt kernel: ? svc_xprt_put+0x12/0x21 [sunrpc]
>> Dec 11 14:58:34 klimt kernel: ? nfsd_svc+0x2be/0x2be [nfsd]
>> Dec 11 14:58:34 klimt kernel: ? nfsd_destroy+0x51/0x51 [nfsd]
>> Dec 11 14:58:34 klimt kernel: svc_process+0xf6/0x115 [sunrpc]
>> Dec 11 14:58:34 klimt kernel: nfsd+0xf2/0x149 [nfsd]
>> Dec 11 14:58:34 klimt kernel: kthread+0xf6/0xfb
>> Dec 11 14:58:34 klimt kernel: ? kthread_queue_delayed_work+0x74/0x74
>> Dec 11 14:58:34 klimt kernel: ret_from_fork+0x3a/0x50
>>
>
> Does something like the following help?
>
> 8<---------------------------------------------------
> From caf515c82ed572e4f92ac8293e5da4818da0c6ce Mon Sep 17 00:00:00 2001
> From: Trond Myklebust <trond.myklebust@hammerspace.com>
> Date: Fri, 13 Dec 2019 15:07:33 -0500
> Subject: [PATCH] nfsd: Fix a soft lockup race in
> nfsd_file_mark_find_or_create()
>
> If nfsd_file_mark_find_or_create() keeps winning the race for the
> nfsd_file_fsnotify_group->mark_mutex against nfsd_file_mark_put()
> then it can soft lock up, since fsnotify_add_inode_mark() ends
> up always finding an existing entry.
>
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> ---
> fs/nfsd/filecache.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
> index 9c2b29e07975..f275c11c4e28 100644
> --- a/fs/nfsd/filecache.c
> +++ b/fs/nfsd/filecache.c
> @@ -132,9 +132,13 @@ nfsd_file_mark_find_or_create(struct nfsd_file *nf)
> struct nfsd_file_mark,
> nfm_mark));
> mutex_unlock(&nfsd_file_fsnotify_group->mark_mutex);
> - fsnotify_put_mark(mark);
> - if (likely(nfm))
> + if (nfm) {
> + fsnotify_put_mark(mark);
> break;
> + }
> + /* Avoid soft lockup race with nfsd_file_mark_put() */
> + fsnotify_destroy_mark(mark, nfsd_file_fsnotify_group);
> + fsnotify_put_mark(mark);
> } else
> mutex_unlock(&nfsd_file_fsnotify_group->mark_mutex);
>

I've tried to reproduce the lockup for three days with this patch
applied to my server. No lockup.

Tested-by: Chuck Lever <chuck.lever@oracle.com>

--
Chuck Lever