[PATCH 5.11 050/601] md: split mddev_find

Greg Kroah-Hartman
2021-05-12T16:53:23Z

From: Christoph Hellwig <hch@lst.de>

commit 65aa97c4d2bfd76677c211b9d03ef05a98c6d68e upstream.

Split mddev_find into a simple mddev_find that just finds an existing
mddev by the unit number, and a more complicated mddev_find that deals
with find or allocating a mddev.

This turns out to fix this bug reported by Zhao Heming.

----------------------------- snip ------------------------------
commit d3374825ce57 ("md: make devices disappear when they are no longer
needed.") introduced protection between mddev creating & removing. The
md_open shouldn't create mddev when all_mddevs list doesn't contain
mddev. With currently code logic, there will be very easy to trigger
soft lockup in non-preempt env.

---
drivers/md/md.c | 24 +++++++++++++++++++-----
1 file changed, 19 insertions(+), 5 deletions(-)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -754,6 +754,22 @@ EXPORT_SYMBOL_GPL(mddev_init);

static struct mddev *mddev_find(dev_t unit)
{
+ struct mddev *mddev;
+
+ if (MAJOR(unit) != MD_MAJOR)
+ unit &= ~((1 << MdpMinorShift) - 1);
+
+ spin_lock(&all_mddevs_lock);
+ mddev = mddev_find_locked(unit);
+ if (mddev)
+ mddev_get(mddev);
+ spin_unlock(&all_mddevs_lock);
+
+ return mddev;
+}
+
+static struct mddev *mddev_find_or_alloc(dev_t unit)
+{
struct mddev *mddev, *new = NULL;

if (unit && MAJOR(unit) != MD_MAJOR)
@@ -5657,7 +5673,7 @@ static int md_alloc(dev_t dev, char *nam
* writing to /sys/module/md_mod/parameters/new_array.
*/
static DEFINE_MUTEX(disks_mutex);
- struct mddev *mddev = mddev_find(dev);
+ struct mddev *mddev = mddev_find_or_alloc(dev);
struct gendisk *disk;
int partitioned;
int shift;
@@ -6539,11 +6555,9 @@ static void autorun_devices(int part)

md_probe(dev);
mddev = mddev_find(dev);
- if (!mddev || !mddev->gendisk) {
- if (mddev)
- mddev_put(mddev);
+ if (!mddev)
break;
- }
+
if (mddev_lock(mddev))
pr_warn("md: %s locked, cannot run\n", mdname(mddev));
else if (mddev->raid_disks || mddev->major_version