Re: bcache-register hang after reboot

[Coly Li <colyli@suse.de>]

On 12/14/21 6:04 AM, Mauricio Faria de Oliveira wrote:
> Hey Kent and Coly,
>
> It turns out that, at least for the disk image that reproduces the issue,
> the closure from bch_btree_set_root() to bch_journal_meta() doesn't make
> a difference; the stall is in bch_journal() -> journal_wait_for_write().
>
> So the previous suggestion to skip bch_journal_meta() altogether works,
> to get things going.. of course, checking for journal replay/full case.
>
> What do you think of this patch?
>
> It simply checks the conditions in run_cache_set() for bch_journal_replay().
> (it starts w/ unlikely(!CACHE_SET_RUNNING) to quickly get to the usual case,
> and apparently has an extra strict check for !gc_thread, just in case.
> And it is journal_full() only, as the !journal_full() case in journal_wait_
> for_write() seems to be handled via another function per the comment.)
>
> This works w/ the disk image here.

Hi Mauricio,

The following patch might work but not a proper fix. I am in travel 
recently, and hope soon I may have time to refine a patch for such 
non-space issue for journal.
I have a patch but it need to be rebased with the latest bcache code.

Thanks.

Coly Li


>
> Thanks!
> Mauricio
>
> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> index 72abe5cf4b12..bedeffc3ae28 100644
> --- a/drivers/md/bcache/btree.c
> +++ b/drivers/md/bcache/btree.c
> @@ -2477,9 +2477,6 @@ int bch_btree_insert(struct cache_set *c, struct keylist *keys,
>   void bch_btree_set_root(struct btree *b)
>   {
>   	unsigned int i;
> -	struct closure cl;
> -
> -	closure_init_stack(&cl);
>   
>   	trace_bcache_btree_set_root(b);
>   
> @@ -2494,8 +2491,18 @@ void bch_btree_set_root(struct btree *b)
>   
>   	b->c->root = b;
>   
> -	bch_journal_meta(b->c, &cl);
> -	closure_sync(&cl);
> +	/* Don't journal during replay if journal is full (prevents deadlock) */
> +	if (unlikely(!test_bit(CACHE_SET_RUNNING, &b->c->flags)) &&
> +	    CACHE_SYNC(&b->c->cache->sb) && b->c->gc_thread == NULL &&
> +	    journal_full(&b->c->journal)) {
> +		pr_info("Not journaling new root (replay with full journal)\n");
> +	} else {
> +		struct closure cl;
> +
> +		closure_init_stack(&cl);
> +		bch_journal_meta(b->c, &cl);
> +		closure_sync(&cl);
> +	}
>   }
>   
>   /* Map across nodes or keys */