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

Ming Lei
2021-10-19T16:30:42Z

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,

--
Ming