在 2022/4/12 5:33, trondmy@xxxxxxxxxx 写道:
From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Any errors reported by the write() system call need to be cleared from
the file descriptor's error tracking. The current call to nfs_wb_all()
causes the error to be reported, but since it doesn't call
file_check_and_advance_wb_err(), we can end up reporting the same error
a second time when the application calls fsync().
Note that since Linux 4.13, the rule is that EIO may be reported for
write(), but it must be reported by a subsequent fsync(), so let's just
drop reporting it in write.
The check for nfs_ctx_key_to_expire() is just a duplicate to the one
already in nfs_write_end(), so let's drop that too.
Reported-by: ChenXiaoSong <chenxiaosong2@xxxxxxxxxx>
Fixes: ce368536dd61 ("nfs: nfs_file_write() should check for writeback errors")
Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
---
fs/nfs/file.c | 33 +++++++++++++--------------------
1 file changed, 13 insertions(+), 20 deletions(-)
# 1. wb error mechanism of other filesystem
Other filesystem only clear the wb error when calling fsync(), async
write will not clear the wb error.
# 2. still report unexpected error ... again
After merging this patchset(5 patches), second `dd` of the following
reproducer will still report unexpected error: No space left on device.
Reproducer:
nfs server | nfs client
------------------------------|---------------------------------------------
# No space left on server |
fallocate -l 100G /svr/nospc |
| mount -t nfs $nfs_server_ip:/ /mnt
|
| # Expected error: No space left on device
| dd if=/dev/zero of=/mnt/file count=1
ibs=10K
|
| # Release space on mountpoint
| rm /mnt/nospc
|
| # Unexpected error: No space left on device
| dd if=/dev/zero of=/mnt/file count=1
ibs=10K
# 3. my patchset
https://patchwork.kernel.org/project/linux-nfs/list/?series=628066
My patchset can fix bug of above reproducer.
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
```
So we still need record writeback error in address_space flags. The
writeback
error in address_space flags is not used to be reported to userspace, it
is just
used to detect if there is new error while writeback.
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.
```c
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)
```
