linux-kernel - Re: [PATCH 4/4] UBI: Implement bitrot checking

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Date:	Sun, 12 Apr 2015 18:14:40 +0200
From:	Richard Weinberger <richard@....at>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
CC:	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	dedekind1@...il.com
Subject: Re: [PATCH 4/4] UBI: Implement bitrot checking

Am 12.04.2015 um 17:14 schrieb Boris Brezillon:
> Second pass on this patch :-).
> 
> On Sun, 29 Mar 2015 14:13:17 +0200
> Richard Weinberger <richard@....at> wrote:
> 
>>  /**
>> + * bitrot_check_worker - physical eraseblock bitrot check worker function.
>> + * @ubi: UBI device description object
>> + * @wl_wrk: the work object
>> + * @shutdown: non-zero if the worker has to free memory and exit
>> + *
>> + * This function reads a physical eraseblock and schedules scrubbing if
>> + * bit flips are detected.
>> + */
>> +static int bitrot_check_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk,
>> +			       int shutdown)
>> +{
>> +	struct ubi_wl_entry *e = wl_wrk->e;
>> +	int err;
>> +
>> +	kfree(wl_wrk);
>> +	if (shutdown) {
>> +		dbg_wl("cancel bitrot check of PEB %d", e->pnum);
>> +		wl_entry_destroy(ubi, e);
>> +		return 0;
>> +	}
>> +
>> +	mutex_lock(&ubi->buf_mutex);
>> +	err = ubi_io_read(ubi, ubi->peb_buf, e->pnum, 0, ubi->peb_size);
>> +	mutex_unlock(&ubi->buf_mutex);
>> +	if (err == UBI_IO_BITFLIPS) {
>> +		dbg_wl("found bitflips in PEB %d", e->pnum);
>> +		spin_lock(&ubi->wl_lock);
>> +
>> +		if (in_pq(ubi, e)) {
>> +			prot_queue_del(ubi, e->pnum);
>> +			wl_tree_add(e, &ubi->scrub);
>> +			spin_unlock(&ubi->wl_lock);
>> +
>> +			err = ensure_wear_leveling(ubi, 1);
>> +		}
>> +		else if (in_wl_tree(e, &ubi->used)) {
>> +			rb_erase(&e->u.rb, &ubi->used);
>> +			wl_tree_add(e, &ubi->scrub);
>> +			spin_unlock(&ubi->wl_lock);
>> +
>> +			err = ensure_wear_leveling(ubi, 1);
>> +		}
>> +		else if (in_wl_tree(e, &ubi->free)) {
>> +			rb_erase(&e->u.rb, &ubi->free);
>> +			spin_unlock(&ubi->wl_lock);
>> +
> 
> IMHO the following code chunk, starting here:
> 
>> +			wl_wrk = prepare_erase_work(e, -1, -1, 1);
>> +			if (IS_ERR(wl_wrk)) {
>> +				err = PTR_ERR(wl_wrk);
>> +				goto out;
>> +			}
>> +
>> +			__schedule_ubi_work(ubi, wl_wrk);
> 
> and ending here ^, could be placed in an helper function
> (re_erase_peb ?)

As long we have only one user of that pattern I'd keep it as is.
We have in UBI already a gazillion helper functions.

>> +			err = 0;
>> +		}
>> +		/*
>> +		 * e is target of a move operation, all we can do is kicking
>> +		 * wear leveling such that we can catch it later or wear
>> +		 * leveling itself scrubbs the PEB.
>> +		 */
>> +		else if (ubi->move_to == e || ubi->move_from == e) {
>> +			spin_unlock(&ubi->wl_lock);
>> +
>> +			err = ensure_wear_leveling(ubi, 1);
>> +		}
>> +		/*
>> +		 * e is member of a fastmap pool. We are not allowed to
>> +		 * remove it from that pool as the on-flash fastmap data
>> +		 * structure refers to it. Let's schedule a new fastmap write
>> +		 * such that the said PEB can get released.
>> +		 */
>> +		else {
>> +			ubi_schedule_fm_work(ubi);
>> +			spin_unlock(&ubi->wl_lock);
>> +
>> +			err = 0;
>> +		}
> 
> I'm nitpicking again, but I like to have a single place where spinlocks
> are locked and unlocked, so here is a rework suggestion for the code
> inside the 'if (err == UBI_IO_BITFLIPS)' statement:

A single lock/unlock place is nice but in this case the whole logic fits
into a single page on screen. "do_this" and "do_that" variables don't make
the code more readable IMHO.
But as with all nitpicks it is a matter of taste and we could waste multiple
days on such things.

Thanks,
//richard
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