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 @@ -736,6 +736,22 @@ 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) @@ -5644,7 +5660,7 @@ 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; @@ -6524,11 +6540,9 @@ 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