Re: [PATCH 01/12] bcache: fix fifo index swapping condition in journal_pin_cmp()

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 2019/11/13 4:03 下午, Coly Li wrote:
> Fifo structure journal.pin is implemented by a cycle buffer, if the back
> index reaches highest location of the cycle buffer, it will be swapped
> to 0. Once the swapping happens, it means a smaller fifo index might be
> associated to a newer journal entry. So the btree node with oldest
> journal entry won't be selected in bch_btree_leaf_dirty() to reference
> the dirty B+tree leaf node. This problem may cause bcache journal won't
> protect unflushed oldest B+tree dirty leaf node in power failure, and
> this B+tree leaf node is possible to beinconsistent after reboot from
> power failure.
> 
> This patch fixes the fifo index comparing logic in journal_pin_cmp(),
> to avoid potential corrupted B+tree leaf node when the back index of
> journal pin is swapped.
> 
> Signed-off-by: Coly Li <colyli@xxxxxxx>

Hi Jens,

Guoju Fang talked to me today, he told me this change was unnecessary
and I was over-thought.

Then I realize fifo_idx() uses a mask to handle the array index overflow
condition, so the index swap in journal_pin_cmp() won't happen. And yes,
Guoju and Kent are correct.

Since you already applied this patch, can you please to remove this
patch from your for-next branch ? This single patch does not break
thing, but it is unecessary at this moment.

Thanks.

Coly Li

> ---
>  drivers/md/bcache/btree.c   | 26 ++++++++++++++++++++++++++
>  drivers/md/bcache/journal.h |  4 ----
>  2 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> index ba434d9ac720..00523cd1db80 100644
> --- a/drivers/md/bcache/btree.c
> +++ b/drivers/md/bcache/btree.c
> @@ -528,6 +528,32 @@ static void btree_node_write_work(struct work_struct *w)
>  	mutex_unlock(&b->write_lock);
>  }
>  
> +/* return true if journal pin 'l' is newer than 'r' */
> +static bool journal_pin_cmp(struct cache_set *c,
> +			    atomic_t *l,
> +			    atomic_t *r)
> +{
> +	int l_idx, r_idx, f_idx, b_idx;
> +	bool ret = false;
> +
> +	l_idx = fifo_idx(&(c)->journal.pin, (l));
> +	r_idx = fifo_idx(&(c)->journal.pin, (r));
> +	f_idx = (c)->journal.pin.front;
> +	b_idx = (c)->journal.pin.back;
> +
> +	if (l_idx > r_idx)
> +		ret = true;
> +	/* in case fifo back pointer is swapped */
> +	if (b_idx < f_idx) {
> +		if (l_idx <= b_idx && r_idx >= f_idx)
> +			ret = true;
> +		else if (l_idx >= f_idx && r_idx <= b_idx)
> +			ret = false;
> +	}
> +
> +	return ret;
> +}
> +
>  static void bch_btree_leaf_dirty(struct btree *b, atomic_t *journal_ref)
>  {
>  	struct bset *i = btree_bset_last(b);
> diff --git a/drivers/md/bcache/journal.h b/drivers/md/bcache/journal.h
> index f2ea34d5f431..06b3eaab7d16 100644
> --- a/drivers/md/bcache/journal.h
> +++ b/drivers/md/bcache/journal.h
> @@ -157,10 +157,6 @@ struct journal_device {
>  };
>  
>  #define BTREE_FLUSH_NR	8
> -
> -#define journal_pin_cmp(c, l, r)				\
> -	(fifo_idx(&(c)->journal.pin, (l)) > fifo_idx(&(c)->journal.pin, (r)))
> -
>  #define JOURNAL_PIN	20000
>  
>  #define journal_full(j)						\
> 



[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [Linux ARM Kernel]     [Linux Filesystem Development]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Security]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [ECOS]     [Asterisk Internet PBX]     [Linux API]

  Powered by Linux