On Fri, Jan 23, 2015 at 10:03:36AM +0900, Minchan Kim wrote:
> 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 <minchan@xxxxxxxxxx>
> > > ---
> > > 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. :)
Argh, sent wrong version.
zram->stats should be protected by the lock but other stat show
functions don't hold a lock so it's racy.
>
> I will fix it. Thanks!
>
>
> >
> > > /*
> > > * Revalidate disk out of the init_lock to avoid lockdep splat.
> > > --
> > > 1.9.3
> > >
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