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SubjectRe: [PATCH] dm writecache: reinitialize lru in writeback instead of endio


On Sat, 30 May 2020, Huaisheng Ye wrote:

> From: Huaisheng Ye <yehs1@lenovo.com>
>
> When wc_entry has been removed from wbl->list in writeback, it will
> be not used again except waiting to be set free in writecache_free_entry.
>
> That is a little of annoying, it has to reinitialize lru of wc_entry
> in endio before calling writecache_free_entry.
>
> Using list_del_init instead of list_del in writeback for simpler code.
>
> Signed-off-by: Huaisheng Ye <yehs1@lenovo.com>

This patch doesn't fix anything, so I think we don't need it.

Actually, it's better to keep the list entry uninitialized, because it
helps us catch bugs where this uninitialized list entry could be used
improperly.

Mikulas

> ---
> drivers/md/dm-writecache.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
> index 7bbc21b..66f3a3b 100644
> --- a/drivers/md/dm-writecache.c
> +++ b/drivers/md/dm-writecache.c
> @@ -1519,7 +1519,6 @@ static void __writecache_endio_pmem(struct dm_writecache *wc, struct list_head *
> e = wb->wc_list[i];
> BUG_ON(!e->write_in_progress);
> e->write_in_progress = false;
> - INIT_LIST_HEAD(&e->lru);
> if (!writecache_has_error(wc))
> writecache_free_entry(wc, e);
> BUG_ON(!wc->writeback_size);
> @@ -1555,7 +1554,6 @@ static void __writecache_endio_ssd(struct dm_writecache *wc, struct list_head *l
> do {
> BUG_ON(!e->write_in_progress);
> e->write_in_progress = false;
> - INIT_LIST_HEAD(&e->lru);
> if (!writecache_has_error(wc))
> writecache_free_entry(wc, e);
>
> @@ -1654,7 +1652,7 @@ static void __writecache_writeback_pmem(struct dm_writecache *wc, struct writeba
> while (wbl->size) {
> wbl->size--;
> e = container_of(wbl->list.prev, struct wc_entry, lru);
> - list_del(&e->lru);
> + list_del_init(&e->lru);
>
> max_pages = e->wc_list_contiguous;
>
> @@ -1685,7 +1683,7 @@ static void __writecache_writeback_pmem(struct dm_writecache *wc, struct writeba
> if (!wc_add_block(wb, f, GFP_NOWAIT | __GFP_NOWARN))
> break;
> wbl->size--;
> - list_del(&f->lru);
> + list_del_init(&f->lru);
> wb->wc_list[wb->wc_list_n++] = f;
> e = f;
> }
> @@ -1712,7 +1710,7 @@ static void __writecache_writeback_ssd(struct dm_writecache *wc, struct writebac
>
> wbl->size--;
> e = container_of(wbl->list.prev, struct wc_entry, lru);
> - list_del(&e->lru);
> + list_del_init(&e->lru);
>
> n_sectors = e->wc_list_contiguous << (wc->block_size_bits - SECTOR_SHIFT);
>
> @@ -1732,7 +1730,7 @@ static void __writecache_writeback_ssd(struct dm_writecache *wc, struct writebac
> wbl->size--;
> f = container_of(wbl->list.prev, struct wc_entry, lru);
> BUG_ON(f != e + 1);
> - list_del(&f->lru);
> + list_del_init(&f->lru);
> e = f;
> }
>
> --
> 1.8.3.1
>

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