Re: [PATCH -next] md: simplify md_seq_ops

On Mon, Sep 11, 2023 at 6:02 PM Yu Kuai [off-list ref] wrote:

[...]

quoted

quoted

+static void *md_seq_start(struct seq_file *seq, loff_t *pos)
+{
+    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);

I would prefer to increase "active" instead holding lock when enumerating over
the devices. the main reason is that parsing mdstat is implemented in mdadm, so
it could kind of blocker action- for example mdmon follows mdstat so it is read
frequently. The time of getting other actions done can highly increase because
every open or sysfs_read/write requires this lock.

Existing code holds pers_lock can seq_printf() in md_seq_show(). Do we see
issues with this?

Hi Kuai,

This patch doesn't apply cleanly to md-next now. Please rebase and send v2.

Thanks,
Song