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f2fs: avoid NULL checkpoint thread access in sysfs

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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: e659206617 ("f2fs: add ckpt_thread_ioprio sysfs node")
Cc: stable@kernel.org
Signed-off-by: Wenjie Qi <qiwenjie@xiaomi.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
This commit is contained in:
Wenjie Qi 2026-08-04 09:48:48 +08:00 committed by Jaegeuk Kim
parent 3de6b80941
commit 5cb33b00c8
1 changed files with 4 additions and 3 deletions
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7
fs/f2fs/sysfs.c
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@ -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)
@ -1007,13 +1007,14 @@ 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);
return ret;