Messages in this thread Patch in this message | | | Date | Wed, 5 Jun 2013 15:29:35 +0900 | From | Minchan Kim <> | Subject | Re: [PATCH v2 03/10] zram: use zram->lock to protect zram_free_page() in swap free notify path |
| |
On Wed, Jun 05, 2013 at 12:06:01AM +0800, Jiang Liu wrote: > zram_free_page() is protected by down_write(&zram->lock) when called by > zram_bvec_write(), but there's no such protection when called by > zram_slot_free_notify(), which may cause wrong states to zram object. > > There are two possible consequences of this issue: > 1) It may cause invalid memory access if we read from a zram device used > as swap device. (Not sure whether it's legal to make read/write > requests to a zram device used as swap device.)
I think it's possible if the permission is allowed so we should take care of that. But I'd like to clear your comment about "invalid memory access".
As I read the code, one of the problem we can encounter by race between zram_bvec_read and zram_slot_free_notify is BUG_ON(!handle) on zs_map_object or pr_err("Decompression failed xxxx) on zram_decompress_page. Otherwise, it would be able to access different swap block with user request's one.
Could you please expand your vague "invalid memory access"?
> 2) It may cause some fields (bad_compress, good_compress, pages_stored) > in zram->stats wrong if the swap layer makes concurrently call to > zram_slot_free_notify(). > > So enhance zram_slot_free_notify() to acquire writer lock on zram->lock > before calling zram_free_page().
OK.
And please add the comment struct zram->lock feild, too.
Thanks.
> > Signed-off-by: Jiang Liu <jiang.liu@huawei.com> > Cc: stable@vger.kernel.org > --- > drivers/staging/zram/zram_drv.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c > index 5a2f20b..847d207 100644 > --- a/drivers/staging/zram/zram_drv.c > +++ b/drivers/staging/zram/zram_drv.c > @@ -582,7 +582,9 @@ static void zram_slot_free_notify(struct block_device *bdev, > struct zram *zram; > > zram = bdev->bd_disk->private_data; > + down_write(&zram->lock); > zram_free_page(zram, index); > + up_write(&zram->lock); > zram_stat64_inc(zram, &zram->stats.notify_free); > } > > -- > 1.8.1.2 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
-- Kind regards, Minchan Kim
| |