Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it

From	NeilBrown <neilb@suse.com>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it
Date	2017-04-05 01:20 +0200
Message-ID	<tsFTX-32H-15@gated-at.bofh.it> (permalink)
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On Tue, Apr 04 2017, Jeff Layton wrote:

> On Tue, 2017-04-04 at 09:12 -0700, Matthew Wilcox wrote:
>> On Tue, Apr 04, 2017 at 08:17:48AM -0400, Jeff Layton wrote:
>> > Agreed that we should focus on POSIX compliance. I'll also note that
>> > POSIX states:
>> > 
>> > "If more than one error occurs in processing a function call, any one
>> > of the possible errors may be returned, as the order of
>> > detection is undefined."
>> > 
>> >     http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_03
>> > 
>> > So, I'd like to push back on this idea that we need to prefer reporting
>> > -EIO over other errors. POSIX certainly doesn't mandate that. 
>> 
>> I honestly wonder if we need to support ENOSPC from writeback at all.
>> Looking at our history, the AS_EIO / AS_ENOSPC came from this patch
>> in 2003:
>> 
>> https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/?id=fcad2b42fc2e15a94ba1a1ba8535681a735bfd16
>> 
>> That seems to come from here:
>> http://lkml.iu.edu/hypermail/linux/kernel/0308.0/0205.html
>> which is marked as a resend, but I can't find the original.
>> 
>> It's a little misleading because the immediately preceding patch
>> introduced mapping->error, so there's no precedent here to speak of.
>> It looks like we used to just silently lose writeback errors (*cough*).
>> 
>> I'd like to suggest that maybe we don't need to support multiple errors
>> at all.  That all errors, including ENOSPC, get collapsed into EIO.
>> POSIX already tells us to do that for close() and permits us to do that
>> for fsync().
>> 
>
> That is certainly allowed under POSIX as I interpret the spec. At a
> minimum we just need a single flag and can collapse all errors under
> that.
>
> That said, I think giving more specific errors where we can is useful.
> When your program is erroring out and writing 'I/O error' to the logs,
> then how much time will your admins burn before they figure out that it
> really failed because the filesystem was full?

What if you don't have an admin?  What if it was an over-quota error?
I think precise error messages are valuable.
I am leaning towards "last error wins" though.  The complexity of any
scheme that reports "worst recent error" seems to out weigh the value.

I think we should present this as a service to filesystems. e.g. create
a "recent_wb_error" structure which the filesystem can record errors in
when they occur, and syscalls can read errors from.
One of these would be provided in 'struct address_space', but
filesystems can easily embed one in their own data structure
(e.g. nfs_open_context) if they want to.

I don't think we should return a recent_wb_error on close by default,
but individual filesystems can ("man 2 close" implies NFS does this for
EDQUOT at it should continue to do so).

fsync() (and file_sync_range()) should return a recent_wb_error, but
what about write()?  It would be a suitable way to stop an application
early, but it isn't exactly the requested write that failed...
Posix says of EIO from write:

    A physical I/O error has occurred.

which is rather vague.  Where and when did this error in physics (:-)
occur?

O_DIRECT write() can get an EIO from a previous write-back write to the
same file.  Maybe non-O_DIRECT writes should too?

Thanks,
NeilBrown

Thread

[RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-03-31 21:30 +0200
  [RFC PATCH 2/4] dax: set errors in mapping when writeback fails Jeff Layton <jlayton@redhat.com> - 2017-03-31 21:30 +0200
  [RFC PATCH 1/4] fs: new infrastructure for writeback error handling and reporting Jeff Layton <jlayton@redhat.com> - 2017-03-31 21:30 +0200
    Re: [RFC PATCH 1/4] fs: new infrastructure for writeback error  handling and reporting Nikolay Borisov <nborisov@suse.com> - 2017-04-03 09:20 +0200
      Re: [RFC PATCH 1/4] fs: new infrastructure for writeback error  handling and reporting Jeff Layton <jlayton@redhat.com> - 2017-04-03 12:30 +0200
    Re: [RFC PATCH 1/4] fs: new infrastructure for writeback error  handling and reporting Matthew Wilcox <willy@infradead.org> - 2017-04-03 16:50 +0200
      Re: [RFC PATCH 1/4] fs: new infrastructure for writeback error  handling and reporting Jeff Layton <jlayton@redhat.com> - 2017-04-03 17:30 +0200
        Re: [RFC PATCH 1/4] fs: new infrastructure for writeback error  handling and reporting Matthew Wilcox <willy@infradead.org> - 2017-04-03 18:20 +0200
          Re: [RFC PATCH 1/4] fs: new infrastructure for writeback error  handling and reporting Jeff Layton <jlayton@redhat.com> - 2017-04-03 18:40 +0200
  [RFC PATCH 4/4] ext4: wire it up to the new writeback error reporting infrastructure Jeff Layton <jlayton@redhat.com> - 2017-03-31 21:30 +0200
  Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-03 06:30 +0200
    Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-03 12:30 +0200
      Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-03 16:40 +0200
        Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-03 19:50 +0200
          Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeremy Allison <jra@samba.org> - 2017-04-03 20:20 +0200
            Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-03 20:20 +0200
              Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeremy Allison <jra@samba.org> - 2017-04-03 20:40 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeremy Allison <jra@samba.org> - 2017-04-03 20:50 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-03 20:50 +0200
          Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-03 21:20 +0200
            Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-03 22:20 +0200
              Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-04 04:50 +0200
              Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-04 05:10 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-04 13:50 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-05 00:50 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-04 14:00 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-04 14:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-04 18:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-04 18:30 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-04 19:10 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-04 20:10 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-05 01:00 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-05 22:00 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-05 23:10 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-06 02:30 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-06 02:10 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-06 05:00 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-06 07:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-06 15:40 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-07 00:00 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-06 16:10 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-06 21:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-06 22:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-07 15:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-10 01:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-10 15:30 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-07 00:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-05 01:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Jeff Layton <jlayton@redhat.com> - 2017-04-05 13:20 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-06 02:50 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Theodore Ts'o <tytso@mit.edu> - 2017-04-04 15:40 +0200
                Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking infrastructure and convert ext4 to use it NeilBrown <neilb@suse.com> - 2017-04-05 00:30 +0200
    Re: [RFC PATCH 0/4] fs: introduce new writeback error tracking  infrastructure and convert ext4 to use it Matthew Wilcox <willy@infradead.org> - 2017-04-03 17:00 +0200

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