[PATCH v2 1/2] f2fs: avoid NULL checkpoint thread access in sysfs

[Wenjie Qi]

checkpoint_merge can be enabled even when no checkpoint merge thread is
running. A read-only mount is one case: f2fs does not start
f2fs_issue_ckpt there, but ckpt_thread_ioprio is still writable through
sysfs.

The ckpt_thread_ioprio store path updates the saved ioprio value and,
when checkpoint_merge is enabled, calls set_task_ioprio() for the
checkpoint thread. If cprc->f2fs_issue_ckpt is NULL, that dereferences a
NULL task pointer.

Keep storing the requested ioprio, but apply it only when the
checkpoint thread exists.

Fixes: e65920661708 ("f2fs: add ckpt_thread_ioprio sysfs node")
Cc: stable@xxxxxxxxxx
Signed-off-by: Wenjie Qi <qiwenjie@xxxxxxxxxx>
---
 fs/f2fs/sysfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
index be92c05a5420..070f9807ae81 100644
--- a/fs/f2fs/sysfs.c
+++ b/fs/f2fs/sysfs.c
@@ -557,7 +557,7 @@ static ssize_t __sbi_store(struct f2fs_attr *a,
 			return -EINVAL;
 
 		cprc->ckpt_thread_ioprio = IOPRIO_PRIO_VALUE(class, level);
-		if (test_opt(sbi, MERGE_CHECKPOINT)) {
+		if (cprc->f2fs_issue_ckpt) {
 			ret = set_task_ioprio(cprc->f2fs_issue_ckpt,
 					cprc->ckpt_thread_ioprio);
 			if (ret)
-- 
2.43.0