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

[chenxiaosong (A)]

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)