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Date:   Wed, 7 Jun 2023 09:27:12 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Naohiro Aota <Naohiro.Aota@wdc.com>
Cc:     Christoph Hellwig <hch@lst.de>, Chris Mason <clm@fb.com>,
        Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>,
        "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH 15/16] btrfs: refactor the zoned device handling in
 cow_file_range
Message-ID: <20230607072712.GA24006@lst.de>
References: <20230531060505.468704-1-hch@lst.de> <20230531060505.468704-16-hch@lst.de> <d4csqyddmdeg2rlzonfsdusggur2anpi3gepwyvjnihbrcnfws@yiiytibnjfb2>
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On Tue, Jun 06, 2023 at 02:20:50PM +0000, Naohiro Aota wrote:
> > +			/*
> > +			 * For zoned devices, let the caller retry after writing
> > +			 * out the already allocated regions or waiting for a
> > +			 * zone to finish if no allocation was possible at all.
> > +			 *
> > +			 * Else convert to -ENOSPC since the caller cannot
> > +			 * retry.
> > +			 */
> > +			if (btrfs_is_zoned(fs_info)) {
> > +				if (start == orig_start)
> > +					return -EAGAIN;
> > +				*done_offset = start - 1;
> 
> This will hit a null pointer dereference when it is called from
> submit_uncompressed_range(). Well, that means we need to implement the
> partial writing also in submit_uncompressed_range().

I think we need to do that anyway, don't we?  As far as I can tell
submit_uncompressed_range is simply broken right now on zoned devices
if cow_file_range fails to allocate all blocks.

> BTW, we also need to handle -EAGAIN from btrfs_reserve_extent() in
> btrfs_new_extent_direct() as it currently returns -EAGAIN to the userland.

Indeed.

> >  			ASSERT(ret == 0);
> >  			return 0;
> >  		}
> > +		if (ret == -EAGAIN) {
> > +			ASSERT(btrfs_is_zoned(inode->root->fs_info));
> 
> Is this necessary? run_delalloc_zoned() should be called only for zoned
> mode anyway.

True.