Hi Trond:
OK, I understand, I will not clear wb err in close(). I will not change
rules that apply to all filesystems.
But if old wb err (such as -ERESTARTSYS or -EINTR, etc.) exist in struct
address_space->wb_err, nfs_file_write() will always return the
unexpected error. 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 // never be error
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
```
I will fix this by store old err before filemap_sample_wb_err(), and
restore old err after filemap_check_wb_err():
```c
// Store the wb err
old_err = file_check_and_advance_wb_err(file)
since = filemap_sample_wb_err()
nfs_wb_all // detect new wb err
error = filemap_check_wb_err(..., since)
// Restore old wb err if no new err is detected
if (!error && old_err)
errseq_set(&file->f_mapping->wb_err, old_err);
```
Is my fixes reasonable ?
