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Date: Sun, 12 May 2024 03:24:47 +0800
From: Kuan-Wei Chiu <visitorckw@gmail.com>
To: Matthew Mirvish <matthew@mm12.xyz>
Cc: Kent Overstreet <kent.overstreet@linux.dev>, Coly Li <colyli@suse.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux Next Mailing List <linux-next@vger.kernel.org>
Subject: Re: linux-next: manual merge of the refactor-heap tree with the
 block tree
Message-ID: <Zj/F/yf0ixB/eRX7@visitorckw-System-Product-Name>
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On Fri, May 10, 2024 at 05:11:02PM +0800, Kuan-Wei Chiu wrote:
> On Thu, May 09, 2024 at 11:46:18PM -0400, Matthew Mirvish wrote:
> > On Fri, May 10, 2024 at 11:07:11AM +0800, Kuan-Wei Chiu wrote:
> > > On Thu, May 09, 2024 at 07:16:31PM -0400, Kent Overstreet wrote:
> > > > On Fri, May 10, 2024 at 06:44:29AM +0800, Kuan-Wei Chiu wrote:
> > > > > On Thu, May 09, 2024 at 03:58:57PM -0400, Kent Overstreet wrote:
> > > > > > On Thu, May 09, 2024 at 03:27:45PM +1000, Stephen Rothwell wrote:
> > > > > > > Hi all,
> > > > > > > 
> > > > > > > Today's linux-next merge of the refactor-heap tree got conflicts in:
> > > > > > > 
> > > > > > >   drivers/md/bcache/bset.c
> > > > > > >   drivers/md/bcache/bset.h
> > > > > > >   drivers/md/bcache/btree.c
> > > > > > >   drivers/md/bcache/writeback.c
> > > > > > > 
> > > > > > > between commit:
> > > > > > > 
> > > > > > >   3a861560ccb3 ("bcache: fix variable length array abuse in btree_iter")
> > > > > > > 
> > > > > > > from the block tree and commit:
> > > > > > > 
> > > > > > >   afa5721abaaa ("bcache: Remove heap-related macros and switch to generic min_heap")
> > > > > > > 
> > > > > > > from the refactor-heap tree.
> > > > > > > 
> > > > > > > Ok, these conflicts are too extensive, so I am dropping the refactor-heap
> > > > > > > tree for today.  I suggest you all get together and sort something out.
> > > > > > 
> > > > > > Coli and Kuan, you guys will need to get this sorted out quick if we
> > > > > > want refactor-heap to make the merge window
> > > > > 
> > > > > Hi Coli and Kent,
> > > > > 
> > > > > If I understand correctly, the reported bug is because we attempted to
> > > > > point (heap)->data to a dynamically allocated memory , but at that time
> > > > > (heap)->data was not a regular pointer but a fixed size array with a
> > > > > length of MAX_BSETS.
> > > > > 
> > > > > In my refactor heap patch series, I introduced a preallocated array and
> > > > > decided in min_heap_init() whether the data pointer should point to an
> > > > > incoming pointer or to the preallocated array. Therefore, I am
> > > > > wondering if my patch might have unintentionally fixed this bug?
> > > > > 
> > > > > I am unsure how to reproduce the reported issue. Could you assist me in
> > > > > verifying whether my assumption is correct?
> > > > 
> > > > This is a merge conflict, not a runtime. Can you rebase onto Coli's
> > > > tree? We'll have to retest.
> > > 
> > > Oh, sorry for the misunderstanding I caused. When I mentioned "bug" [1]
> > > earlier, I was referring to the bug addressed in
> > > 3a861560ccb3 ("bcache: fix variable length array abuse in btree_iter"),
> > > not a merge conflict.
> > > 
> > > Here are the results after the rebase:
> > > https://github.com/visitorckw/linux.git refactor-heap
> > > 
> > > [1]: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2039368
> > 
> > The ubuntu kernels build with UBSAN now, and the bug reported is just a
> > UBSAN warning. The original implementation's iterator has a fixed size
> > sets array that is indexed out of bounds when the iterator is allocated
> > on the heap with more space -- the patch restructures it a bit to have a
> > single iterator type with a flexible array and then a larger "stack"
> > type which embeds the iterator along with the preallocated region.
> > 
> > I took a brief look at the refactor-heap branch but I'm not entirely
> > sure what's going on with the new min heaps: in the one place where the
> > larger iterators are used (in bch_btree_node_read_done) it doesn't look
> > like the heap is ever initialized (perhaps since the old iter_init
> > wasn't used here because of the special case it got missed in the
> > refactor?) With the new heaps it should be fairly easy to fix though;
> > just change the fill_iter mempool to be allocating only the minheap data
> > arrays and setup iter->heap.data properly with that instead.
> 
> Thank you, Matthew.
> Not initializing the heap's data pointer was indeed my mistake.
> Following your advice, I made the following modifications to the code
> on the refactor-heap branch in my github repo. I hope this time it
> works well.
>
Should I resend it as a patch series?

> 
> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> index a2bb86d52ad4..ce9d729bc8ff 100644
> --- a/drivers/md/bcache/btree.c
> +++ b/drivers/md/bcache/btree.c
> @@ -149,19 +149,19 @@ void bch_btree_node_read_done(struct btree *b)
>  {
>  	const char *err = "bad btree header";
>  	struct bset *i = btree_bset_first(b);
> -	struct btree_iter *iter;
> +	struct btree_iter iter;
> 
>  	/*
>  	 * c->fill_iter can allocate an iterator with more memory space
>  	 * than static MAX_BSETS.
>  	 * See the comment arount cache_set->fill_iter.
>  	 */
> -	iter = mempool_alloc(&b->c->fill_iter, GFP_NOIO);
> -	iter->heap.size = b->c->cache->sb.bucket_size / b->c->cache->sb.block_size;
> -	iter->heap.nr = 0;
> +	iter.heap.data = mempool_alloc(&b->c->fill_iter, GFP_NOIO);
> +	iter.heap.size = b->c->cache->sb.bucket_size / b->c->cache->sb.block_size;
> +	iter.heap.nr = 0;
> 
>  #ifdef CONFIG_BCACHE_DEBUG
> -	iter->b = &b->keys;
> +	iter.b = &b->keys;
>  #endif
> 
>  	if (!i->seq)
> @@ -199,7 +199,7 @@ void bch_btree_node_read_done(struct btree *b)
>  		if (i != b->keys.set[0].data && !i->keys)
>  			goto err;
> 
> -		bch_btree_iter_push(iter, i->start, bset_bkey_last(i));
> +		bch_btree_iter_push(&iter, i->start, bset_bkey_last(i));
> 
>  		b->written += set_blocks(i, block_bytes(b->c->cache));
>  	}
> @@ -211,7 +211,7 @@ void bch_btree_node_read_done(struct btree *b)
>  		if (i->seq == b->keys.set[0].data->seq)
>  			goto err;
> 
> -	bch_btree_sort_and_fix_extents(&b->keys, iter, &b->c->sort);
> +	bch_btree_sort_and_fix_extents(&b->keys, &iter, &b->c->sort);
> 
>  	i = b->keys.set[0].data;
>  	err = "short btree key";
> @@ -223,7 +223,7 @@ void bch_btree_node_read_done(struct btree *b)
>  		bch_bset_init_next(&b->keys, write_block(b),
>  				   bset_magic(&b->c->cache->sb));
>  out:
> -	mempool_free(iter, &b->c->fill_iter);
> +	mempool_free(iter.heap.data, &b->c->fill_iter);
>  	return;
>  err:
>  	set_btree_node_io_error(b);
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index cba09660148a..c6f5592996a8 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -1914,8 +1914,7 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
>  	INIT_LIST_HEAD(&c->btree_cache_freed);
>  	INIT_LIST_HEAD(&c->data_buckets);
> 
> -	iter_size = sizeof(struct btree_iter) +
> -		    ((meta_bucket_pages(sb) * PAGE_SECTORS) / sb->block_size) *
> +	iter_size = ((meta_bucket_pages(sb) * PAGE_SECTORS) / sb->block_size) *
>  			    sizeof(struct btree_iter_set);
> 
>  	c->devices = kcalloc(c->nr_uuids, sizeof(void *), GFP_KERNEL);
>