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Message-ID: <d319b6b9-13b5-6ce0-5aba-1635fb381e15@huawei.com>
Date:   Tue, 12 Apr 2022 22:25:49 +0800
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Subject: Re: [PATCH v2 3/5] NFS: Don't report ENOSPC write errors twice
From:   "chenxiaosong (A)" <chenxiaosong2@huawei.com>
To:     Trond Myklebust <trondmy@hammerspace.com>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        "trondmy@kernel.org" <trondmy@kernel.org>
CC:     "smayhew@redhat.com" <smayhew@redhat.com>,
        "zhangxiaoxu5@huawei.com" <zhangxiaoxu5@huawei.com>,
        "yi.zhang@huawei.com" <yi.zhang@huawei.com>
References: <20220411213346.762302-1-trondmy@kernel.org>
 <20220411213346.762302-2-trondmy@kernel.org>
 <20220411213346.762302-3-trondmy@kernel.org>
 <20220411213346.762302-4-trondmy@kernel.org>
 <a2babe9f-e85e-3c72-9132-35aa6ae3888b@huawei.com>
 <5fde4fd533805990cfbd0f23964db786cfda2cd7.camel@hammerspace.com>
 <3536f67c-95f3-efbf-3d0f-0b7e8b4549b9@huawei.com>
 <52552874-01a4-d0da-8904-1b81659e5d1c@huawei.com>
In-Reply-To: <52552874-01a4-d0da-8904-1b81659e5d1c@huawei.com>
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在 2022/4/12 21:29, chenxiaosong (A) 写道:
> 在 2022/4/12 21:13, chenxiaosong (A) 写道:
> On other filesystem, wb error is only cleared when doing fsync() or sync 
> write(), it should not clear the wb error when doing async write(). Your 
> patch will clear the wb error when doing async write().
> 
> And my patchset mainly fix following problem:
> 
> filemap_sample_wb_err() always return 0 if old writeback error
> have not been consumed. filemap_check_wb_err() will return the old error
> even if there is no new writeback error between filemap_sample_wb_err() and
> filemap_check_wb_err().
> 
> ```c
>    since = filemap_sample_wb_err() = 0
>      errseq_sample
>        if (!(old & ERRSEQ_SEEN)) // nobody see the error
>          return 0;
>    nfs_wb_all // no new error
>    error = filemap_check_wb_err(..., since) != 0 // unexpected error
> ```
> 

After merging your patchset, NFS will report and clear wb error on 
_async_ write(), even there is no new wb error while nfs_wb_all, is this 
reasonable?

And more importantly, we can not detect new error by using 
filemap_sample_wb_err()/filemap_check_wb_err() while nfs_wb_all(),just 
as I described:

```c
   since = filemap_sample_wb_err() = 0
     errseq_sample
       if (!(old & ERRSEQ_SEEN)) // nobody see the error
         return 0;
   nfs_wb_all // no new error
   error = filemap_check_wb_err(..., since) != 0 // unexpected error
```
.