On Tue, Oct 19, 2021 at 12:36:42PM -0700, Luis Chamberlain wrote:

On Wed, Oct 20, 2021 at 12:29:53AM +0800, Ming Lei wrote:

quoted

On Tue, Oct 19, 2021 at 08:28:21AM -0700, Luis Chamberlain wrote:

quoted

On Tue, Oct 19, 2021 at 10:34:41AM +0800, Ming Lei wrote:

quoted

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

Again, you are running two zram02.sh[1] on /dev/zram0, that isn't unexpected
behavior. Here the difference is just timing. In my test VM,
this message shows a while on one task, then it may be switched to
another task.

Just run your patches a while, nothing real difference here, and the
following message can be dumped from one task for long time:

	can't set '107374182400' to /sys/block/zram0/disksize

Also you did not answer my question about your test expected result when
running the following script from two terminal concurrently:

	while true; do
		PATH=$PATH:$PWD:$PWD/../../../lib/ ./zram02.sh;
	done




Thanks,
Ming