Re: [PATCH v8 11/12] zram: fix crashes with cpu hotplug multistate

Luis Chamberlain
2021-10-19T19:37:00Z

On Wed, Oct 20, 2021 at 12:29:53AM +0800, Ming Lei wrote:
> On Tue, Oct 19, 2021 at 08:28:21AM -0700, Luis Chamberlain wrote:
> > On Tue, Oct 19, 2021 at 10:34:41AM +0800, Ming Lei wrote:
> > > Please try the following patch against upstream(linus or next) tree(basically
> > > fold revised 2 and 3 of V1, and cover two issues: not fail zram_remove in
> > > module_exit(), race between zram_remove() and disksize_store()), and see if
> > > everything is fine for you:
> >
> > Page fault ...
> >
> > [ 18.284256] zram: Removed device: zram0
> > [ 18.312974] BUG: unable to handle page fault for address:
> > ffffad86de903008
> > [ 18.313707] #PF: supervisor read access in kernel mode
> > [ 18.314248] #PF: error_code(0x0000) - not-present page
> > [ 18.314797] PGD 100000067 P4D 100000067 PUD 10031e067 PMD 136a28067
>
> That is another race between zram_reset_device() and disksize_store(),
> which is supposed to be covered by ->init_lock, and follows the delta fix
> against the last patch I posted, and the whole patch can be found in the
> github link:
>
> https://github.com/ming1/linux/commit/fa6045b1371eb301f392ac84adaf3ad53bb16894
>
>
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index d0cae7a42f4d..a14ba3d350ea 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1704,12 +1704,12 @@ static void zram_reset_device(struct zram *zram)
> set_capacity_and_notify(zram->disk, 0);
> part_stat_set_all(zram->disk->part0, 0);
>
> - up_write(&zram->init_lock);
> /* I/O operation under all of CPU are done so let's free */
> zram_meta_free(zram, disksize);
> memset(&zram->stats, 0, sizeof(zram->stats));
> zcomp_destroy(comp);
> reset_bdev(zram);
> + up_write(&zram->init_lock);
> }
>
> static ssize_t disksize_store(struct device *dev,

With this, it still ends up in a state where we loop and can't get out of:

zram: Can't change algorithm for initialized device

Luis