linux-kernel - Re: [PATCH 4.19 19/71] btrfs: extent_io: add proper error handling to lock_extent_buffer_for

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Date:   Wed, 11 Nov 2020 14:39:34 +0000
From:   Ben Hutchings <ben.hutchings@...ethink.co.uk>
To:     Pavel Machek <pavel@....cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Qu Wenruo <wqu@...e.com>, David Sterba <dsterba@...e.com>
Subject: Re: [PATCH 4.19 19/71] btrfs: extent_io: add proper error handling
 to lock_extent_buffer_for_io()

On Wed, 2020-11-11 at 13:44 +0100, Pavel Machek wrote:
> Hi!
> 
> > Thankfully it's handled by the only caller, btree_write_cache_pages(),
> > as later write_one_eb() call will trigger submit_one_bio().  So there
> > shouldn't be any problem.
> 
> This explains there should not be any problem in _the
> mainline_. AFAICT this talks about this code. Mainline version is:
> 
>  prev_eb = eb;
>  ret = lock_extent_buffer_for_io(eb, &epd);
>  if (!ret) {
>  	free_extent_buffer(eb);
>  	continue;
>  } else if (ret < 0) {
>  	done = 1;
>  	free_extent_buffer(eb);
>  	break;
>  }
> 
> But 4.19 has:
> 
>  ret = lock_extent_buffer_for_io(eb, fs_info, &epd);
>  if (!ret) {
>   	free_extent_buffer(eb);
>  	continue;
>  }

That was changed in mainline two releases after this commit, though.

> IOW missing the code mentioned in the changelog. Is 0607eb1d452d4
> prerequisite for this patch?

I think it's a separate fix, but probably worth picking too.

Ben.

> Best regards,
> 								Pavel
> 
> > +/*
> > + * Lock eb pages and flush the bio if we can't the locks
> > + *
> > + * Return  0 if nothing went wrong
> > + * Return >0 is same as 0, except bio is not submitted
> > + * Return <0 if something went wrong, no page is locked
> > + */
-- 
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom