md: Fix md_seq_ops() regressions

Commit cf1b6d4441ff ("md: simplify md_seq_ops") introduce following
regressions:

1) If list all_mddevs is emptly, personalities and unused devices won't
   be showed to user anymore.
2) If seq_file buffer overflowed from md_seq_show(), then md_seq_start()
   will be called again, hence personalities will be showed to user
   again.
3) If seq_file buffer overflowed from md_seq_stop(), seq_read_iter()
   doesn't handle this, hence unused devices won't be showed to user.

Fix above problems by printing personalities and unused devices in
md_seq_show().

Fixes: cf1b6d4441ff ("md: simplify md_seq_ops")
Cc: stable@vger.kernel.org # v6.7+
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20240109133957.2975272-1-yukuai1@huaweicloud.com

diff --git a/drivers/md/md.c b/drivers/md/md.c
index e351e6c..ff3057c 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8135,6 +8135,19 @@ static void status_unused(struct seq_file *seq)
        seq_printf(seq, "\n");
 }
 
+static void status_personalities(struct seq_file *seq)
+{
+       struct md_personality *pers;
+
+       seq_puts(seq, "Personalities : ");
+       spin_lock(&pers_lock);
+       list_for_each_entry(pers, &pers_list, list)
+               seq_printf(seq, "[%s] ", pers->name);
+
+       spin_unlock(&pers_lock);
+       seq_puts(seq, "\n");
+}
+
 static int status_resync(struct seq_file *seq, struct mddev *mddev)
 {
        sector_t max_sectors, resync, res;
@@ -8276,20 +8289,10 @@ static int status_resync(struct seq_file *seq, struct mddev *mddev)
 static void *md_seq_start(struct seq_file *seq, loff_t *pos)
        __acquires(&all_mddevs_lock)
 {
-       struct md_personality *pers;
-
-       seq_puts(seq, "Personalities : ");
-       spin_lock(&pers_lock);
-       list_for_each_entry(pers, &pers_list, list)
-               seq_printf(seq, "[%s] ", pers->name);
-
-       spin_unlock(&pers_lock);
-       seq_puts(seq, "\n");
        seq->poll_event = atomic_read(&md_event_count);
-
        spin_lock(&all_mddevs_lock);
 
-       return seq_list_start(&all_mddevs, *pos);
+       return seq_list_start_head(&all_mddevs, *pos);
 }
 
 static void *md_seq_next(struct seq_file *seq, void *v, loff_t *pos)
@@ -8300,16 +8303,23 @@ static void *md_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 static void md_seq_stop(struct seq_file *seq, void *v)
        __releases(&all_mddevs_lock)
 {
-       status_unused(seq);
        spin_unlock(&all_mddevs_lock);
 }
 
 static int md_seq_show(struct seq_file *seq, void *v)
 {
-       struct mddev *mddev = list_entry(v, struct mddev, all_mddevs);
+       struct mddev *mddev;
        sector_t sectors;
        struct md_rdev *rdev;
 
+       if (v == &all_mddevs) {
+               status_personalities(seq);
+               if (list_empty(&all_mddevs))
+                       status_unused(seq);
+               return 0;
+       }
+
+       mddev = list_entry(v, struct mddev, all_mddevs);
        if (!mddev_get(mddev))
                return 0;
 
@@ -8385,6 +8395,10 @@ static int md_seq_show(struct seq_file *seq, void *v)
        }
        spin_unlock(&mddev->lock);
        spin_lock(&all_mddevs_lock);
+
+       if (mddev == list_last_entry(&all_mddevs, struct mddev, all_mddevs))
+               status_unused(seq);
+
        if (atomic_dec_and_test(&mddev->active))
                __mddev_put(mddev);