Hello,
On Wed, Jan 21, 2015 at 11:21:53PM +0900, Sergey Senozhatsky wrote:
> On (01/21/15 15:14), Minchan Kim wrote:
> > We don't need to call zram_meta_free under init_lock.
> > What we need to prevent race is setting NULL into zram->meta
> > (ie, init_done). This patch does it.
> >
> > Signed-off-by: Minchan Kim <minc...@kernel.org>
> > ---
> > drivers/block/zram/zram_drv.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index 9250b3f..7e03d86 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -719,6 +719,8 @@ static void zram_reset_device(struct zram *zram, bool
> > reset_capacity)
> > }
> >
> > meta = zram->meta;
> > + zram->meta = NULL;
> > +
> > /* Free all pages that are still in this zram device */
> > for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
> > unsigned long handle = meta->table[index].handle;
> > @@ -731,8 +733,6 @@ static void zram_reset_device(struct zram *zram, bool
> > reset_capacity)
> > zcomp_destroy(zram->comp);
> > zram->max_comp_streams = 1;
> >
> > - zram_meta_free(zram->meta);
> > - zram->meta = NULL;
> > /* Reset stats */
> > memset(&zram->stats, 0, sizeof(zram->stats));
> >
> > @@ -741,6 +741,7 @@ static void zram_reset_device(struct zram *zram, bool
> > reset_capacity)
> > set_capacity(zram->disk, 0);
> >
> > up_write(&zram->init_lock);
> > + zram_meta_free(meta);
>
> Hello,
>
> since we detached ->meta from zram, this one doesn't really need
> ->init_lock protection:
>
> /* Free all pages that are still in this zram device */
> for (index = 0; index < zram->disksize >> PAGE_SHIFT; index++) {
> unsigned long handle = meta->table[index].handle;
> if (!handle)
> continue;
>
> zs_free(meta->mem_pool, handle);
> }
>
>
> -ss
Good catch.
As well, we could move zcomp_destroy and memset(&zram->stats)
out of the lock but zram_rw_page, ZRAM_ATTR_RO, disksize_show
and orig_data_size_show have a race bug which access stats
out of the lock so that it could show the stale vaule.
Although it's not a significant, there is no reason to hesitate the fix. :)
I will fix it. Thanks!
>
> > /*
> > * Revalidate disk out of the init_lock to avoid lockdep splat.
> > --
> > 1.9.3
> >
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