4.9-stable review patch. If anyone has any objections, please let me know.
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From: NeilBrown neilb@suse.com
commit 39772f0a7be3b3dc26c74ea13fe7847fd1522c8b upstream.
The locking protocols in md assume that a device will never be removed from an array during resync/recovery/reshape. When that isn't happening, rcu or reconfig_mutex is needed to protect an rdev pointer while taking a refcount. When it is happening, that protection isn't needed.
Unfortunately there are cases were remove_and_add_spares() is called when recovery might be happening: is state_store(), slot_store() and hot_remove_disk(). In each case, this is just an optimization, to try to expedite removal from the personality so the device can be removed from the array. If resync etc is happening, we just have to wait for md_check_recover to find a suitable time to call remove_and_add_spares().
This optimization and not essential so it doesn't matter if it fails. So change remove_and_add_spares() to abort early if resync/recovery/reshape is happening, unless it is called from md_check_recovery() as part of a newly started recovery. The parameter "this" is only NULL when called from md_check_recovery() so when it is NULL, there is no need to abort.
As this can result in a NULL dereference, the fix is suitable for -stable.
cc: yuyufen yuyufen@huawei.com Cc: Tomasz Majchrzak tomasz.majchrzak@intel.com Fixes: 8430e7e0af9a ("md: disconnect device from personality before trying to remove it.") Cc: stable@ver.kernel.org (v4.8+) Signed-off-by: NeilBrown neilb@suse.com Signed-off-by: Shaohua Li sh.li@alibaba-inc.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/md/md.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -8224,6 +8224,10 @@ static int remove_and_add_spares(struct int removed = 0; bool remove_some = false;
+ if (this && test_bit(MD_RECOVERY_RUNNING, &mddev->recovery)) + /* Mustn't remove devices when resync thread is running */ + return 0; + rdev_for_each(rdev, mddev) { if ((this == NULL || rdev == this) && rdev->raid_disk >= 0 &&