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Date: Tue, 13 Oct 2015 10:13:04 -0400
Message-ID: <CAN-5tyGme1rm+hD0JpOc3co0=_u2hzPwR7eN3AT4_TjVA4NkDA@mail.gmail.com>
Subject: Re: [PATCH 1/1] Adding issync field to delegreturn_exit tracepoint
From: Olga Kornievskaia <aglo@umich.edu>
To: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: linux-nfs <linux-nfs@vger.kernel.org>
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Sender: linux-nfs-owner@vger.kernel.org

On Tue, Oct 13, 2015 at 9:27 AM, Trond Myklebust
<trond.myklebust@primarydata.com> wrote:
> On Tue, Oct 13, 2015 at 8:26 AM, Olga Kornievskaia <aglo@umich.edu> wrote:
>>
>> On Mon, Oct 12, 2015 at 11:47 PM, Trond Myklebust
>> <trond.myklebust@primarydata.com> wrote:
>> > On Mon, Oct 12, 2015 at 5:55 PM, Olga Kornievskaia <aglo@umich.edu> wrote:
>> >> It'll be nice to know when we return delegations synchronously or not.
>> >
>> > Why? This patch forces us to carry an otherwise completely unnecessary
>> > parameter, so at the very minimum we should have a discussion of what
>> > the real use cases are.
>>
>> I used it to diagnose the race of open and delegreturn. If it's kept
>
> How were you using it?

 I added two more traces points in the beginning of delegreturn and in
nfs4_do_open before sending the rpc. I can see that a given file
handle:
-- delegreturn prepare tracepoint is happening,
-- then the tracepoint of before sending the open is logged,
-- then delegreturn prepare is logged again,
-- then tracepoint for nfs4_open_file which is after receiving reply
to the open from the server
-- then delegreturn_exit tracepoint

    kworker/1:0H-14168 [001] ....   576.571636:
nfs4_delegreturn_prepare: error=0 (OK) dev=00:2a fhandle=0x84792ca9
issync=0

          hammer-13955 [000] ....   576.942632: nfs4_open_file_begin:
flags=32768 (0x8000) fmode=READ|0x801c fileid=00:2a:0
fhandle=0x00000000 name=00:2a:904/000002CB.ham

          hammer-13955 [001] ....   577.043084: nfs4_open_file:
error=0 (OK) flags=32768 (0x8000) fmode=READ|0x801c fileid=00:2a:7708
fhandle=0x84792ca9 name=00:2a:904/000002CB.ham

    kworker/0:1H-431   [000] ....   577.064013:
nfs4_delegreturn_prepare: error=0 (OK) dev=00:2a fhandle=0x84792ca9
issync=0

    kworker/0:1H-431   [000] ....   577.101076: nfs4_delegreturn_exit:
error=0 (OK) dev=00:2a fhandle=0x84792ca9

    kworker/0:1H-431   [000] ....   577.113021: nfs4_read:
error=-10025 (BAD_STATEID) fileid=00:2a:7708 fhandle=0x84792ca9
offset=0 count=64


>
>> that some delegreturns are synchronous and others are not I think the
>> information is useful.
>
> The only difference between synchronous and asynchronous in this case
> is whether or not the process that launched the delegreturn actually
> waits for it to complete; a signal could easily prevent it from doing
> so without interrupting the delegreturn call itself.
> IOW: for complete information when debugging races here, you really
> need to examine the return value from the wait call.
>
>> Speaking of there is a race between state manager thread returning
>> used delegations and new open. Previously I thought it was evict
>> inode...
>
> Is this with commit 5e99b532bb95 ("nfs4: reset states to use
> open_stateid when returning delegation voluntarily") applied?

No I have not. I will try that. Thanks.