[PATCH v2 1/6] zram: do not permit params change after init

[Sergey Senozhatsky <senozhatsky@chromium.org>]

First, algorithm_params_store(), like any sysfs handler,
should grab device lock.

Second, like any write() sysfs handler, it should grab
device lock in exclusive mode.

Third, it should not permit change of algos' parameters
after device init, as this doesn't make sense - we cannot
compress with one C/D dict and then just change C/D dict
to a different one, for example.

Another thing to notice is that algorithm_params_store()
accesses device's ->comp_algs for algo priority lookup,
which should be protected by device lock in exclusive
mode in general.

Fixes: 4eac932103a5d ("zram: introduce algorithm_params device attribute")
Acked-by: Brian Geffon <bgeffon@google.com>
Cc: gao xu <gaoxu2@honor.com>
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zram_drv.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index fa38d26119ec..db862179cf59 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1750,6 +1750,10 @@ static ssize_t algorithm_params_store(struct device *dev,
 		}
 	}
 
+	guard(rwsem_write)(&zram->dev_lock);
+	if (init_done(zram))
+		return -EBUSY;
+
 	/* Lookup priority by algorithm name */
 	if (algo) {
 		s32 p;
-- 
2.53.0.473.g4a7958ca14-goog