Re: [PATCH] pnfs: devide put_lseg and return_layout_barrier into different workqueue

[Zhang Jingwang <yyalone@gmail.com>]

2010/5/17 Boaz Harrosh <bharrosh@panasas.com>:
> On 05/17/2010 12:59 PM, Zhang Jingwang wrote:
>> These two functions mustn't be called from the same workqueue. Otherwise
>> deadlock may occur. So we schedule the return_layout_barrier to nfsiod.
>> nfsiod may not be a good choice, maybe we should setup a new workqueue
>> to do the job.
>
> Please give more information. When does it happen that pnfs_XXX_done will
> return -EAGAIN?
network error or something else.

>
> What is the stack trace of the deadlock?
>
http://linux-nfs.org/pipermail/pnfs/2010-January/009939.html

> And please rebase that patch on the latest changes to _pnfs_return_layout().
> but since in the new code _pnfs_return_layout() must be called with NO_WAIT
> if called from the nfsiod then you cannot call pnfs_initiate_write/read() right
> after. For writes you can get by with doing nothing because the write-back
> thread will kick in soon enough. For reads I'm not sure, you'll need to send
> me more information, stack trace.
>
> Or you can wait for the new state machine.
I think the reason of this deadlock is that the put and the wait are
in the same workqueue and run serially. So the state machine will not
help.
>
> Boaz
>
>>
>> Signed-off-by: Zhang Jingwang <zhangjingwang@nrchpc.ac.cn>
>> ---
>>  fs/nfs/pnfs.c |   58 +++++++++++++++++++++++++++++++++++++++-----------------
>>  1 files changed, 40 insertions(+), 18 deletions(-)
>>
>> diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
>> index 5ad7fc6..d2b72be 100644
>> --- a/fs/nfs/pnfs.c
>> +++ b/fs/nfs/pnfs.c
>> @@ -1655,6 +1655,24 @@ pnfs_call_done(struct pnfs_call_data *pdata, struct rpc_task *task, void *data)
>>   * cleanup.
>>   */
>>  static void
>> +pnfs_write_retry(struct work_struct *work)
>> +{
>> +     struct rpc_task *task;
>> +     struct nfs_write_data *wdata;
>> +     struct nfs4_pnfs_layout_segment range;
>> +
>> +     dprintk("%s enter\n", __func__);
>> +     task = container_of(work, struct rpc_task, u.tk_work);
>> +     wdata = container_of(task, struct nfs_write_data, task);
>> +     range.iomode = IOMODE_RW;
>> +     range.offset = wdata->args.offset;
>> +     range.length = wdata->args.count;
>> +     _pnfs_return_layout(wdata->inode, &range, NULL, RETURN_FILE);
>> +     pnfs_initiate_write(wdata, NFS_CLIENT(wdata->inode),
>> +                         wdata->pdata.call_ops, wdata->pdata.how);
>> +}
>> +
>> +static void
>>  pnfs_writeback_done(struct nfs_write_data *data)
>>  {
>>       struct pnfs_call_data *pdata = &data->pdata;
>> @@ -1674,15 +1692,8 @@ pnfs_writeback_done(struct nfs_write_data *data)
>>       }
>>
>>       if (pnfs_call_done(pdata, &data->task, data) == -EAGAIN) {
>> -             struct nfs4_pnfs_layout_segment range = {
>> -                     .iomode = IOMODE_RW,
>> -                     .offset = data->args.offset,
>> -                     .length = data->args.count,
>> -             };
>> -             dprintk("%s: retrying\n", __func__);
>> -             _pnfs_return_layout(data->inode, &range, NULL, RETURN_FILE);
>> -             pnfs_initiate_write(data, NFS_CLIENT(data->inode),
>> -                                 pdata->call_ops, pdata->how);
>> +             INIT_WORK(&data->task.u.tk_work, pnfs_write_retry);
>> +             queue_work(nfsiod_workqueue, &data->task.u.tk_work);
>>       }
>>  }
>>
>> @@ -1798,6 +1809,24 @@ out:
>>   * read_pagelist is done
>>   */
>>  static void
>> +pnfs_read_retry(struct work_struct *work)
>> +{
>> +     struct rpc_task *task;
>> +     struct nfs_read_data *rdata;
>> +     struct nfs4_pnfs_layout_segment range;
>> +
>> +     dprintk("%s enter\n", __func__);
>> +     task = container_of(work, struct rpc_task, u.tk_work);
>> +     rdata = container_of(task, struct nfs_read_data, task);
>> +     range.iomode = IOMODE_RW;
>> +     range.offset = rdata->args.offset;
>> +     range.length = rdata->args.count;
>> +     _pnfs_return_layout(rdata->inode, &range, NULL, RETURN_FILE);
>> +     pnfs_initiate_read(rdata, NFS_CLIENT(rdata->inode),
>> +                        rdata->pdata.call_ops);
>> +}
>> +
>> +static void
>>  pnfs_read_done(struct nfs_read_data *data)
>>  {
>>       struct pnfs_call_data *pdata = &data->pdata;
>> @@ -1805,15 +1834,8 @@ pnfs_read_done(struct nfs_read_data *data)
>>       dprintk("%s: Begin (status %d)\n", __func__, data->task.tk_status);
>>
>>       if (pnfs_call_done(pdata, &data->task, data) == -EAGAIN) {
>> -             struct nfs4_pnfs_layout_segment range = {
>> -                     .iomode = IOMODE_ANY,
>> -                     .offset = data->args.offset,
>> -                     .length = data->args.count,
>> -             };
>> -             dprintk("%s: retrying\n", __func__);
>> -             _pnfs_return_layout(data->inode, &range, NULL, RETURN_FILE);
>> -             pnfs_initiate_read(data, NFS_CLIENT(data->inode),
>> -                                pdata->call_ops);
>> +             INIT_WORK(&data->task.u.tk_work, pnfs_read_retry);
>> +             queue_work(nfsiod_workqueue, &data->task.u.tk_work);
>>       }
>>  }
>>
>
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-- 
Zhang Jingwang
National Research Centre for High Performance Computers
Institute of Computing Technology, Chinese Academy of Sciences
No. 6, South Kexueyuan Road, Haidian District
Beijing, China