On (23/11/07 21:19), Vasily Averin wrote:
> On 11/7/23 13:40, Sergey Senozhatsky wrote:
> > On (23/11/07 16:39), Sergey Senozhatsky wrote:
> >> Hmmm,
> >> We may want to do more here. Basically, we probably need to re-confirm
> >> after read_from_bdev() that the entry at index still has ZRAM_WB set
> >> and, if so, that it points to the same blk_idx. IOW, check that it has
> >> not been free-ed and re-used under us.
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -1364,14 +1364,21 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
> > ret = zram_read_from_zspool(zram, page, index);
> > zram_slot_unlock(zram, index);
> > } else {
> > + unsigned long idx = zram_get_element(zram, index);
> > /*
> > * The slot should be unlocked before reading from the backing
> > * device.
> > */
> > zram_slot_unlock(zram, index);
> >
> > - ret = read_from_bdev(zram, page, zram_get_element(zram, index),
> > - parent);
> > + ret = read_from_bdev(zram, page, idx, parent);
> > + if (ret == 0) {
> > + zram_slot_lock(zram, index);
> > + if (!zram_test_flag(zram, index, ZRAM_WB) ||
> > + idx != zram_get_element(zram, index))
> > + ret = -EINVAL;
> > + zram_slot_unlock(zram, index);
> > + }
>
> Why overwritten page can not be pushed to WB to the same blk_idx?
Yeah, so I thought about it too but didn't want to go too deep into it.
We probably can only address it if we synchronize free_page (?), read_page()
and writeback(), so that we never have concurrent bitmap modifications when
one of the operations is in progress.
