[PATCH v2 1/4] samples/damon: fix damon sample prcl for start failure

[Honggyu Kim <honggyu.kim@sk.com>]

The damon_sample_prcl_start() can fail so we must reset the "enable"
parameter to "false" again for proper rollback.

In such cases, setting Y to "enable" then N triggers the following
crash because damon sample start failed but the "enable" stays as Y.

  [ 2441.419649] damon_sample_prcl: start
  [ 2454.146817] damon_sample_prcl: stop
  [ 2454.146862] ------------[ cut here ]------------
  [ 2454.146865] kernel BUG at mm/slub.c:546!
  [ 2454.148183] Oops: invalid opcode: 0000 [#1] SMP NOPTI
  	...
  [ 2454.167555] Call Trace:
  [ 2454.167822]  <TASK>
  [ 2454.168061]  damon_destroy_ctx+0x78/0x140
  [ 2454.168454]  damon_sample_prcl_enable_store+0x8d/0xd0
  [ 2454.168932]  param_attr_store+0xa1/0x120
  [ 2454.169315]  module_attr_store+0x20/0x50
  [ 2454.169695]  sysfs_kf_write+0x72/0x90
  [ 2454.170065]  kernfs_fop_write_iter+0x150/0x1e0
  [ 2454.170491]  vfs_write+0x315/0x440
  [ 2454.170833]  ksys_write+0x69/0xf0
  [ 2454.171162]  __x64_sys_write+0x19/0x30
  [ 2454.171525]  x64_sys_call+0x18b2/0x2700
  [ 2454.171900]  do_syscall_64+0x7f/0x680
  [ 2454.172258]  ? exit_to_user_mode_loop+0xf6/0x180
  [ 2454.172694]  ? clear_bhb_loop+0x30/0x80
  [ 2454.173067]  ? clear_bhb_loop+0x30/0x80
  [ 2454.173439]  entry_SYSCALL_64_after_hwframe+0x76/0x7e

Fixes: 2aca254620a8 ("samples/damon: introduce a skeleton of a smaple DAMON module for proactive reclamation")
Signed-off-by: Honggyu Kim <honggyu.kim@sk.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
---
 samples/damon/prcl.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/samples/damon/prcl.c b/samples/damon/prcl.c
index 056b1b21a0fe..5597e6a08ab2 100644
--- a/samples/damon/prcl.c
+++ b/samples/damon/prcl.c
@@ -122,8 +122,12 @@ static int damon_sample_prcl_enable_store(
 	if (enable == enabled)
 		return 0;
 
-	if (enable)
-		return damon_sample_prcl_start();
+	if (enable) {
+		err = damon_sample_prcl_start();
+		if (err)
+			enable = false;
+		return err;
+	}
 	damon_sample_prcl_stop();
 	return 0;
 }
-- 
2.34.1