md/bitmap: don't set max_write_behind if there is no write mostly device

We shouldn't set it since write behind IO should only happen to write
mostly device.

Signed-off-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Signed-off-by: Song Liu <songliubraving@fb.com>

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index e29c629..bfd6026 100644 (file)
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -2469,11 +2469,30 @@ backlog_store(struct mddev *mddev, const char *buf, size_t len)
 {
        unsigned long backlog;
        unsigned long old_mwb = mddev->bitmap_info.max_write_behind;
+       struct md_rdev *rdev;
+       bool has_write_mostly = false;
        int rv = kstrtoul(buf, 10, &backlog);
        if (rv)
                return rv;
        if (backlog > COUNTER_MAX)
                return -EINVAL;
+
+       /*
+        * Without write mostly device, it doesn't make sense to set
+        * backlog for max_write_behind.
+        */
+       rdev_for_each(rdev, mddev) {
+               if (test_bit(WriteMostly, &rdev->flags)) {
+                       has_write_mostly = true;
+                       break;
+               }
+       }
+       if (!has_write_mostly) {
+               pr_warn_ratelimited("%s: can't set backlog, no write mostly device available\n",
+                                   mdname(mddev));
+               return -EINVAL;
+       }
+
        mddev->bitmap_info.max_write_behind = backlog;
        if (!backlog && mddev->serial_info_pool) {
                /* serial_info_pool is not needed if backlog is zero */