linux-kernel - Re: [PATCH -next,v2 0/3] nfs: handle writeback errors correctly

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Date:   Mon, 11 Apr 2022 22:15:09 +0800
From:   "chenxiaosong (A)" <chenxiaosong2@...wei.com>
To:     <trond.myklebust@...merspace.com>, <anna@...nel.org>,
        <smayhew@...hat.com>
CC:     <linux-nfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <liuyongqiang13@...wei.com>, <yi.zhang@...wei.com>,
        <zhangxiaoxu5@...wei.com>
Subject: Re: [PATCH -next,v2 0/3] nfs: handle writeback errors correctly

ping ...

在 2022/4/1 15:03, chenxiaosong (A) 写道:
> 在 2022/4/1 11:44, ChenXiaoSong 写道:
>> v1:
>> cover letter: (nfs: check writeback errors correctly)
>>
>> v2:
>> - return more nuanced writeback errors in nfs_file_write().
>> - return writeback error in close()->flush() without consumed it.
>> - fix: nfs_file_write() will always call nfs_wb_all() even if there is no
>> new writeback error.
>>
>>
>> ChenXiaoSong (3):
>>    NFS: return more nuanced writeback errors in nfs_file_write()
>>    NFS: nfs{,4}_file_flush() return correct writeback errors
>>    Revert "nfs: nfs_file_write() should check for writeback errors"
>>
>>   fs/nfs/file.c     | 23 ++++++++++-------------
>>   fs/nfs/nfs4file.c |  8 ++++----
>>   fs/nfs/write.c    |  5 +----
>>   3 files changed, 15 insertions(+), 21 deletions(-)
>>
> 
> It is not a good idea to modify error sequence mechanism, as the 
> `lib/errseq.c` described:
> 
>      22  * Note that there is a risk of collisions if new errors are 
> being recorded
>      23  * frequently, since we have so few bits to use as a counter.
>      24  *
>      25  * To mitigate this, one bit is used as a flag to tell whether 
> the value has
>      26  * been sampled since a new value was recorded. That allows us 
> to avoid bumping
>      27  * the counter if no one has sampled it since the last time an 
> error was
>      28  * recorded.
> 
> 
> So, if we want to report nuanced writeback error, it is better to detect 
> wb error from filemap_check_errors(), and then return 
> -(file->f_mapping->wb_err & MAX_ERRNO) to userspace without consume it.
> 
>    nfs_mapping_set_error
>      mapping_set_error
>        __filemap_set_wb_err // record error sequence
>          errseq_set
>        set_bit(..., &mapping->flags) // record address_space flag
> 
>    // it is not used to be reported, just used to detect
>    error = filemap_check_errors // -ENOSPC or -EIO
>      test_and_clear_bit(..., &mapping->flags) // error bit cleared
> 
>    // now we try to return nuanced writeback error
>    if (error)
>    return filemap_check_wb_err(file->f_mapping, 0);
>      return -(file->f_mapping->wb_err & MAX_ERRNO)
>