linux-kernel - Re: [PATCH -next 1/2] nfs: nfs{,4}_file_flush should consume writeback error

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Message-ID: <5666cb64-c9e4-0549-6ddb-cfc877c9c071@huawei.com>
Date:   Sun, 6 Mar 2022 11:54:04 +0800
From:   "chenxiaosong (A)" <chenxiaosong2@...wei.com>
To:     Trond Myklebust <trondmy@...merspace.com>,
        "anna@...nel.org" <anna@...nel.org>,
        "smayhew@...hat.com" <smayhew@...hat.com>
CC:     "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "liuyongqiang13@...wei.com" <liuyongqiang13@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "yi.zhang@...wei.com" <yi.zhang@...wei.com>,
        "zhangxiaoxu5@...wei.com" <zhangxiaoxu5@...wei.com>,
        ChenXiaoSong <chenxiaosong2@...wei.com>
Subject: Re: [PATCH -next 1/2] nfs: nfs{,4}_file_flush should consume
 writeback error

It would be more clear if I update the reproducer like this:

         nfs server                 |       nfs client
  --------------------------------- |---------------------------------
  # No space left on server         |
  fallocate -l 100G /server/nospace |
                                    | mount -t nfs $nfs_server_ip:/ /mnt
                                    |
                                    | # Expected error
                                    | dd if=/dev/zero of=/mnt/file
                                    |
                                    | # Release space on mountpoint
                                    | rm /mnt/nospace
                                    |
                                    | # Unexpected error
                                    | dd if=/dev/zero of=/mnt/file

The Unexpected error (No space left on device) when doing second `dd`, 
is from unconsumed writeback error after close() the file when doing 
first `dd`. There is enough space when doing second `dd`, we should not 
report the nospace error.

We should report and consume the writeback error when userspace call 
close()->flush(), the writeback error should not be left for next open().

Currently, fsync() will consume the writeback error while calling 
file_check_and_advance_wb_err(), close()->flush() should also consume 
the writeback error.


在 2022/3/6 0:53, Trond Myklebust 写道:
> 'rm' doesn't open any files or do any I/O, so it shouldn't be returning
> any errors from the page cache.
> 
> IOW: The problem here is not that we're failing to clear an error from
> the page cache. It is that something in 'rm' is checking the page cache
> and returning any errors that it finds there.
> 
> Is 'rm' perhaps doing a stat() on the file it is deleting? If so, does
> this patch fix the bug?
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/comm
> it/?id=d19e0183a883
>