Hello Dongsheng Yang,
Commit 1d57628ff95b ("dm-pcache: add persistent cache target in
device-mapper") from Aug 12, 2025 (linux-next), leads to the
following Smatch static checker warning:
drivers/md/dm-pcache/cache_segment.c:263 cache_seg_gen_increase()
warn: sleeping in atomic context
drivers/md/dm-pcache/cache_segment.c
257 static void cache_seg_gen_increase(struct pcache_cache_segment
*cache_seg)
258 {
259 spin_lock(&cache_seg->gen_lock);
260 cache_seg->gen++;
261 spin_unlock(&cache_seg->gen_lock);
262
--> 263 cache_seg_ctrl_write(cache_seg);
cache_seg_ctrl_write() takes a mutex so it can't be called with
preemption disabled.
264 }
There are a few callers which Smatch says have preemption disabled:
The call tree is kind of messy but the point is that there are four
callers which Smatch says disable preemption.
miss_read_end_req() <- disables preempt
-> cache_data_alloc() <- disables preempt
miss_read_end_req() <- disables preempt <duplicate>
cache_write() <- disables preempt
-> cache_seg_put()
-> cache_seg_invalidate()
-> cache_seg_gen_increase()
drivers/md/dm-pcache/cache_req.c
36 static int cache_data_alloc(struct pcache_cache *cache, struct
pcache_cache_key *key)
37 {
38 struct pcache_cache_data_head *data_head;
39 struct pcache_cache_pos *head_pos;
40 struct pcache_cache_segment *cache_seg;
41 u32 seg_remain;
42 u32 allocated = 0, to_alloc;
43 int ret = 0;
44
45 preempt_disable();
^^^^^^^^^^^^^^^^^^
46 data_head = get_data_head(cache);
47 again:
48 to_alloc = key->len - allocated;
49 if (!data_head->head_pos.cache_seg) {
50 seg_remain = 0;
51 } else {
52 cache_pos_copy(&key->cache_pos, &data_head->head_pos);
53 key->seg_gen = key->cache_pos.cache_seg->gen;
54
55 head_pos = &data_head->head_pos;
56 cache_seg = head_pos->cache_seg;
57 seg_remain = cache_seg_remain(head_pos);
58 }
59
60 if (seg_remain > to_alloc) {
61 /* If remaining space in segment is sufficient for the
cache key, allocate it. */
62 cache_pos_advance(head_pos, to_alloc);
63 allocated += to_alloc;
64 cache_seg_get(cache_seg);
65 } else if (seg_remain) {
66 /* If remaining space is not enough, allocate the
remaining space and adjust the cache key length. */
67 cache_pos_advance(head_pos, seg_remain);
68 key->len = seg_remain;
69
70 /* Get for key: obtain a reference to the cache segment
for the key. */
71 cache_seg_get(cache_seg);
72 /* Put for head_pos->cache_seg: release the reference
for the current head's segment. */
73 cache_seg_put(head_pos->cache_seg);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
If we still are holding a second reference, then this warning is a false
positive, but the commen suggests that we might actually free it.
74 head_pos->cache_seg = NULL;
75 } else {
76 /* Initialize a new data head if no segment is
available. */
77 ret = cache_data_head_init(cache);
78 if (ret)
79 goto out;
80
81 goto again;
82 }
83
84 out:
85 preempt_enable();
86
87 return ret;
88 }
regards,
dan carpenter
