[PATCH 4/4] zram: add init_done() guard to algorithm_params_store()

[Andrew Stellman]

algorithm_params_store() allows writing compression parameters after
the zram device has been initialized. Peer sysfs store functions
(comp_algorithm_store, disksize_store, mem_limit_store) all check
init_done(zram) and return -EBUSY when the device is already in use.
algorithm_params_store() uniquely lacks this guard, allowing runtime
mutation of compression parameters on an active device.

Acquire dev_lock and check init_done() immediately before calling
comp_params_store(), after argument parsing and priority resolution
complete. This keeps the lock scope narrow and matches the pattern in
__comp_algorithm_store().

Signed-off-by: Andrew Stellman <astellman@xxxxxxxxxxxxxxxxxxx>
---
 drivers/block/zram/zram_drv.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 67dea80..d270964 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1772,6 +1772,12 @@ static ssize_t algorithm_params_store(struct device *dev,
 	if (prio < ZRAM_PRIMARY_COMP || prio >= ZRAM_MAX_COMPS)
 		return -EINVAL;
 
+	guard(rwsem_write)(&zram->dev_lock);
+	if (init_done(zram)) {
+		pr_info("Can't change algorithm params for initialized device\n");
+		return -EBUSY;
+	}
+
 	ret = comp_params_store(zram, prio, level, dict_path, &deflate_params);
 	return ret ? ret : len;
 }
-- 
2.34.1