6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Wenjie Qi commit 5cb33b00c8fbb6e8f1fa3d281c3036d5f7c7c41f upstream. 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. Protect ckpt_thread_ioprio sysfs writes with s_umount as well, so the checkpoint thread cannot disappear under the store path while updating its ioprio. Fixes: e65920661708 ("f2fs: add ckpt_thread_ioprio sysfs node") Cc: stable@kernel.org Signed-off-by: Wenjie Qi Reviewed-by: Chao Yu Signed-off-by: Jaegeuk Kim Signed-off-by: Greg Kroah-Hartman --- fs/f2fs/sysfs.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) --- a/fs/f2fs/sysfs.c +++ b/fs/f2fs/sysfs.c @@ -547,7 +547,7 @@ out: 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) @@ -962,13 +962,14 @@ static ssize_t f2fs_sbi_store(struct f2f 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); return ret;