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

[Chao Yu <chao@kernel.org>]

This patch should include below change? otherwise it's not a self-contained
fix.

@@ -1007,13 +1007,15 @@ static ssize_t f2fs_sbi_store(struct f2fs_attr *a,
  	ssize_t ret;
  	bool gc_entry = (!strcmp(a->attr.name, "gc_urgent") ||
  					a->struct_type == GC_THREAD);
+	bool thread_entry = !strcmp(a->attr.name, "ckpt_thread_ioprio");

-	if (gc_entry) {
+	if (gc_entry || thread_entry) {
  		if (!down_read_trylock(&sbi->sb->s_umount))
  			return -EAGAIN;
  	}
  	ret = __sbi_store(a, sbi, buf, count);
-	if (gc_entry)
+	if (gc_entry || thread_entry)
  		up_read(&sbi->sb->s_umount);

On 8/3/26 17:23, Wenjie Qi wrote:
> 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@kernel.org
> Signed-off-by: Wenjie Qi <qiwenjie@xiaomi.com>
> ---
>   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)