md: make reconfig_mutex optional for writes to md sysfs files.

Rather than using mddev_lock() to take the reconfig_mutex
when writing to any md sysfs file, we only take mddev_lock()
in the particular _store() functions that require it.
Admittedly this is most, but it isn't all.

This also allows us to remove special-case handling for new_dev_store
(in md_attr_store).

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 76 insertions, 58 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index d5b80174b3b3..aa76865b804b 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5400,21 +5400,25 @@ EXPORT_SYMBOL(raid5_set_cache_size);
 static ssize_t
 raid5_store_stripe_cache_size(struct mddev *mddev, const char *page, size_t len)
 {
-        struct r5conf *conf = mddev->private;
+        struct r5conf *conf;
         unsigned long new;
         int err;
 
         if (len >= PAGE_SIZE)
                 return -EINVAL;
-        if (!conf)
-                return -ENODEV;
-
         if (kstrtoul(page, 10, &new))
                 return -EINVAL;
-        err = raid5_set_cache_size(mddev, new);
+        err = mddev_lock(mddev);
         if (err)
                 return err;
-        return len;
+        conf = mddev->private;
+        if (!conf)
+                err = -ENODEV;
+        else
+                err = raid5_set_cache_size(mddev, new);
+        mddev_unlock(mddev);
+
+        return err ?: len;
 }
 
 static struct md_sysfs_entry
@@ -5438,19 +5442,27 @@ raid5_show_preread_threshold(struct mddev *mddev, char *page)
 static ssize_t
 raid5_store_preread_threshold(struct mddev *mddev, const char *page, size_t len)
 {
-        struct r5conf *conf = mddev->private;
+        struct r5conf *conf;
         unsigned long new;
+        int err;
+
         if (len >= PAGE_SIZE)
                 return -EINVAL;
-        if (!conf)
-                return -ENODEV;
-
         if (kstrtoul(page, 10, &new))
                 return -EINVAL;
-        if (new > conf->max_nr_stripes)
-                return -EINVAL;
-        conf->bypass_threshold = new;
-        return len;
+
+        err = mddev_lock(mddev);
+        if (err)
+                return err;
+        conf = mddev->private;
+        if (!conf)
+                err = -ENODEV;
+        else if (new > conf->max_nr_stripes)
+                err = -EINVAL;
+        else
+                conf->bypass_threshold = new;
+        mddev_unlock(mddev);
+        return err ?: len;
 }
 
 static struct md_sysfs_entry
@@ -5475,29 +5487,35 @@ raid5_show_skip_copy(struct mddev *mddev, char *page)
 static ssize_t
 raid5_store_skip_copy(struct mddev *mddev, const char *page, size_t len)
 {
-        struct r5conf *conf = mddev->private;
+        struct r5conf *conf;
         unsigned long new;
+        int err;
+
         if (len >= PAGE_SIZE)
                 return -EINVAL;
-        if (!conf)
-                return -ENODEV;
-
         if (kstrtoul(page, 10, &new))
                 return -EINVAL;
         new = !!new;
-        if (new == conf->skip_copy)
-                return len;
 
-        mddev_suspend(mddev);
-        conf->skip_copy = new;
-        if (new)
-                mddev->queue->backing_dev_info.capabilities |=
-                                                BDI_CAP_STABLE_WRITES;
-        else
-                mddev->queue->backing_dev_info.capabilities &=
-                                                ~BDI_CAP_STABLE_WRITES;
-        mddev_resume(mddev);
-        return len;
+        err = mddev_lock(mddev);
+        if (err)
+                return err;
+        conf = mddev->private;
+        if (!conf)
+                err = -ENODEV;
+        else if (new != conf->skip_copy) {
+                mddev_suspend(mddev);
+                conf->skip_copy = new;
+                if (new)
+                        mddev->queue->backing_dev_info.capabilities |=
+                                BDI_CAP_STABLE_WRITES;
+                else
+                        mddev->queue->backing_dev_info.capabilities &=
+                                ~BDI_CAP_STABLE_WRITES;
+                mddev_resume(mddev);
+        }
+        mddev_unlock(mddev);
+        return err ?: len;
 }
 
 static struct md_sysfs_entry
@@ -5538,7 +5556,7 @@ static int alloc_thread_groups(struct r5conf *conf, int cnt,
 static ssize_t
 raid5_store_group_thread_cnt(struct mddev *mddev, const char *page, size_t len)
 {
-        struct r5conf *conf = mddev->private;
+        struct r5conf *conf;
         unsigned long new;
         int err;
         struct r5worker_group *new_groups, *old_groups;
@@ -5546,41 +5564,41 @@ raid5_store_group_thread_cnt(struct mddev *mddev, const char *page, size_t len)
 
         if (len >= PAGE_SIZE)
                 return -EINVAL;
-        if (!conf)
-                return -ENODEV;
-
         if (kstrtoul(page, 10, &new))
                 return -EINVAL;
 
-        if (new == conf->worker_cnt_per_group)
-                return len;
-
-        mddev_suspend(mddev);
+        err = mddev_lock(mddev);
+        if (err)
+                return err;
+        conf = mddev->private;
+        if (!conf)
+                err = -ENODEV;
+        else if (new != conf->worker_cnt_per_group) {
+                mddev_suspend(mddev);
 
-        old_groups = conf->worker_groups;
-        if (old_groups)
-                flush_workqueue(raid5_wq);
+                old_groups = conf->worker_groups;
+                if (old_groups)
+                        flush_workqueue(raid5_wq);
 
-        err = alloc_thread_groups(conf, new,
-                                  &group_cnt, &worker_cnt_per_group,
-                                  &new_groups);
-        if (!err) {
-                spin_lock_irq(&conf->device_lock);
-                conf->group_cnt = group_cnt;
-                conf->worker_cnt_per_group = worker_cnt_per_group;
-                conf->worker_groups = new_groups;
-                spin_unlock_irq(&conf->device_lock);
+                err = alloc_thread_groups(conf, new,
+                                          &group_cnt, &worker_cnt_per_group,
+                                          &new_groups);
+                if (!err) {
+                        spin_lock_irq(&conf->device_lock);
+                        conf->group_cnt = group_cnt;
+                        conf->worker_cnt_per_group = worker_cnt_per_group;
+                        conf->worker_groups = new_groups;
+                        spin_unlock_irq(&conf->device_lock);
 
-                if (old_groups)
-                        kfree(old_groups[0].workers);
-                kfree(old_groups);
+                        if (old_groups)
+                                kfree(old_groups[0].workers);
+                        kfree(old_groups);
+                }
+                mddev_resume(mddev);
         }
+        mddev_unlock(mddev);
 
-        mddev_resume(mddev);
-
-        if (err)
-                return err;
-        return len;
+        return err ?: len;
 }
 
 static struct md_sysfs_entry