Re: [bug report] task hang while testing xfstests generic/323

[Trond Myklebust <trondmy@hammerspace.com>]

On Fri, 2019-03-01 at 16:49 +0800, Jiufei Xue wrote:
> 
> On 2019/3/1 下午1:08, Jiufei Xue wrote:
> > Hi Olga,
> > 
> > On 2019/3/1 上午6:26, Olga Kornievskaia wrote:
> > > On Thu, Feb 28, 2019 at 5:11 AM Jiufei Xue <
> > > jiufei.xue@linux.alibaba.com> wrote:
> > > > Hi,
> > > > 
> > > > when I tested xfstests/generic/323 with NFSv4.1 and v4.2, the
> > > > task
> > > > changed to zombie occasionally while a thread is hanging with
> > > > the
> > > > following stack:
> > > > 
> > > > [<0>] rpc_wait_bit_killable+0x1e/0xa0 [sunrpc]
> > > > [<0>] nfs4_do_close+0x21b/0x2c0 [nfsv4]
> > > > [<0>] __put_nfs_open_context+0xa2/0x110 [nfs]
> > > > [<0>] nfs_file_release+0x35/0x50 [nfs]
> > > > [<0>] __fput+0xa2/0x1c0
> > > > [<0>] task_work_run+0x82/0xa0
> > > > [<0>] do_exit+0x2ac/0xc20
> > > > [<0>] do_group_exit+0x39/0xa0
> > > > [<0>] get_signal+0x1ce/0x5d0
> > > > [<0>] do_signal+0x36/0x620
> > > > [<0>] exit_to_usermode_loop+0x5e/0xc2
> > > > [<0>] do_syscall_64+0x16c/0x190
> > > > [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > > > [<0>] 0xffffffffffffffff
> > > > 
> > > > Since commit 12f275cdd163(NFSv4: Retry CLOSE and DELEGRETURN on
> > > > NFS4ERR_OLD_STATEID), the client will retry to close the file
> > > > when
> > > > stateid generation number in client is lower than server.
> > > > 
> > > > The original intention of this commit is retrying the operation
> > > > while
> > > > racing with an OPEN. However, in this case the stateid
> > > > generation remains
> > > > mismatch forever.
> > > > 
> > > > Any suggestions?
> > > 
> > > Can you include a network trace of the failure? Is it possible
> > > that
> > > the server has crashed on reply to the close and that's why the
> > > task
> > > is hung? What server are you testing against?
> > > 
> > I am testing the local server, the testcase is attached below.
> > 
> > # uname -r
> > 5.0.0-rc8
> > 
> > # cat /etc/exports
> > /mnt/vdd *(rw,no_subtree_check,no_root_squash)
> > 
> > # cat test.sh
> > mount /dev/vdd /mnt/vdd
> > systemctl start nfs
> > mount -t nfs -o rw,relatime,vers=4.1 127.0.0.1:/mnt/vdd
> > /mnt/nfsscratch
> > 
> > for ((i=0;i<10000;i++))
> > do
> >         echo "loop $i started"
> >         /usr/local/xfstests/src/aio-dio-regress/aio-last-ref-held-
> > by-io 1 100 /mnt/nfsscratch/aio-testfile
> > 	sleep 5
> > done
> > 
> > The command aio-last-ref-held-by-io from xfstests will spawn 100
> > threads. Each thread
> > repeated doing open/io_submit/close/io_getevents/io_destroy until
> > the parent exist
> > because of timeout.
> > 
> > 
> > Here is the log when the task hung.
> > 
> > [10841.121523] nfs4_close_prepare: begin!
> > [10841.121526] --> nfs4_alloc_slot used_slots=0000
> > highest_used=4294967295 max_slots=10
> > [10841.121528] <-- nfs4_alloc_slot used_slots=0001 highest_used=0
> > slotid=0
> > [10841.121530] nfs4_close_prepare: done!
> > [10841.121536] encode_sequence: sessionid=1551405749:3822331530:1:0
> > seqid=59495845 slotid=0 max_slotid=0 cache_this=1
> > [10841.121583] nfsd_dispatch: vers 4 proc 1
> > [10841.121588] __find_in_sessionid_hashtbl:
> > 1551405749:3822331530:1:0
> > [10841.121590] nfsd4_sequence: slotid 0
> > [10841.121592] check_slot_seqid enter. seqid 59495845 slot_seqid
> > 59495844
> > [10841.121596] nfsd: fh_verify(28: 01060001 0c66c6db d74ea4c9
> > 61e12d9e c03beba6 0000000b)
> > [10841.121607] nfsd: fh_verify(28: 01060001 0c66c6db d74ea4c9
> > 61e12d9e c03beba6 0000000b)
> > [10841.121613] NFSD: nfsd4_close on file aio-testfile
> > [10841.121615] NFSD: nfs4_preprocess_seqid_op: seqid=0 stateid =
> > (5c7892b5/e3d4268a/000ab905/0000746b)
> > [10841.121619] nfsv4 compound returned 10024
> > [10841.121621] --> nfsd4_store_cache_entry slot 00000000f540ddd9
> > [10841.121625] renewing client (clientid 5c7892b5/e3d4268a)
> > [10841.122526] decode_attr_type: type=00
> > ......
> > [10841.122558] nfs4_close_done: begin!
> > [10841.122561] --> nfs4_alloc_slot used_slots=0001 highest_used=0
> > max_slots=10
> > [10841.122564] <-- nfs4_alloc_slot used_slots=0003 highest_used=1
> > slotid=1
> > [10841.122566] nfs4_free_slot: slotid 1 highest_used_slotid 0
> > [10841.122568] nfs41_sequence_process: Error 0 free the slot
> > [10841.122571] nfs4_free_slot: slotid 0 highest_used_slotid
> > 4294967295
> > [10841.122575] nfs4_close_done: done, ret = 0!
> > [10841.122584] nfs4_close_prepare: begin!
> > ......
> > Client keep retry the CLOSE.
> > 
> > > I have seen trace where close would get ERR_OLD_STATEID and would
> > > still retry with the same open state until it got a reply to the
> > > OPEN
> > > which changed the state and when the client received reply to
> > > that,
> > > it'll retry the CLOSE with the updated stateid.
> > > 
> > 
> > Yes, you are right. I have also noticed that. But what happened if
> > the
> > OPEN task exit receiving a signal? How can a client update the
> > stateid?
> > 

static void nfs4_open_release(void *calldata)
{
        struct
nfs4_opendata *data = calldata;
        struct nfs4_state *state = NULL;

        /* If this request hasn't been cancelled, do nothing */
        if (!data->cancelled)
                goto out_free;
        /* In case of error, no cleanup! */
        if (data->rpc_status != 0 || !data->rpc_done)
                goto out_free;
        /* In case we need an open_confirm, no cleanup! */
        if (data->o_res.rflags & NFS4_OPEN_RESULT_CONFIRM)
                goto out_free;
        state = nfs4_opendata_to_nfs4_state(data);
        if (!IS_ERR(state))
                nfs4_close_state(state, data->o_arg.fmode);
out_free:
        nfs4_opendata_put(data);
}

Note what happens when the 'data->cancelled' flag is set. This is why
we always ensure that stateful operations such as OPEN, and LOCK,...
are run as asynchronous RPC tasks.
OPEN_DOWNGRADE, CLOSE and LOCKU are also asynchronous, but they are
inherently safe against signals since they do not establish new state
that needs to be torn down.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com