md/raid5: use ->lock to protect accessing raid5 sysfs attributes.

It is important that mddev->private isn't freed while
a sysfs attribute function is accessing it.

So use mddev->lock to protect the setting of ->private to NULL, and
take that lock when checking ->private for NULL and de-referencing it
in the sysfs access functions.

This only applies to the read ('show') side of access.  Write
access will be handled separately.

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

1 files changed, 28 insertions, 16 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index dab908b2aa9a..d5b80174b3b3 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5354,11 +5354,14 @@ static void raid5d(struct md_thread *thread)
 static ssize_t
 raid5_show_stripe_cache_size(struct mddev *mddev, char *page)
 {
-        struct r5conf *conf = mddev->private;
+        struct r5conf *conf;
+        int ret = 0;
+        spin_lock(&mddev->lock);
+        conf = mddev->private;
         if (conf)
-                return sprintf(page, "%d\n", conf->max_nr_stripes);
-        else
-                return 0;
+                ret = sprintf(page, "%d\n", conf->max_nr_stripes);
+        spin_unlock(&mddev->lock);
+        return ret;
 }
 
 int
@@ -5422,11 +5425,14 @@ raid5_stripecache_size = __ATTR(stripe_cache_size, S_IRUGO | S_IWUSR,
 static ssize_t
 raid5_show_preread_threshold(struct mddev *mddev, char *page)
 {
-        struct r5conf *conf = mddev->private;
+        struct r5conf *conf;
+        int ret = 0;
+        spin_lock(&mddev->lock);
+        conf = mddev->private;
         if (conf)
-                return sprintf(page, "%d\n", conf->bypass_threshold);
-        else
-                return 0;
+                ret = sprintf(page, "%d\n", conf->bypass_threshold);
+        spin_unlock(&mddev->lock);
+        return ret;
 }
 
 static ssize_t
@@ -5456,11 +5462,14 @@ raid5_preread_bypass_threshold = __ATTR(preread_bypass_threshold,
 static ssize_t
 raid5_show_skip_copy(struct mddev *mddev, char *page)
 {
-        struct r5conf *conf = mddev->private;
+        struct r5conf *conf;
+        int ret = 0;
+        spin_lock(&mddev->lock);
+        conf = mddev->private;
         if (conf)
-                return sprintf(page, "%d\n", conf->skip_copy);
-        else
-                return 0;
+                ret = sprintf(page, "%d\n", conf->skip_copy);
+        spin_unlock(&mddev->lock);
+        return ret;
 }
 
 static ssize_t
@@ -5512,11 +5521,14 @@ raid5_stripecache_active = __ATTR_RO(stripe_cache_active);
 static ssize_t
 raid5_show_group_thread_cnt(struct mddev *mddev, char *page)
 {
-        struct r5conf *conf = mddev->private;
+        struct r5conf *conf;
+        int ret = 0;
+        spin_lock(&mddev->lock);
+        conf = mddev->private;
         if (conf)
-                return sprintf(page, "%d\n", conf->worker_cnt_per_group);
-        else
-                return 0;
+                ret = sprintf(page, "%d\n", conf->worker_cnt_per_group);
+        spin_unlock(&mddev->lock);
+        return ret;
 }
 
 static int alloc_thread_groups(struct r5conf *conf, int cnt,