linux-kernel - [PATCH 3.2 053/153] ubi: Fix race condition between ubi volume creation and udev

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Date:   Wed, 30 May 2018 11:52:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Clay McClure" <clay@...mons.net>,
        "Richard Weinberger" <richard@....at>
Subject: [PATCH 3.2 053/153] ubi: Fix race condition between ubi volume
 creation and udev

3.2.102-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Clay McClure <clay@...mons.net>

commit a51a0c8d213594bc094cb8e54aad0cb6d7f7b9a6 upstream.

Similar to commit 714fb87e8bc0 ("ubi: Fix race condition between ubi
device creation and udev"), we should make the volume active before
registering it.

Signed-off-by: Clay McClure <clay@...mons.net>
Signed-off-by: Richard Weinberger <richard@....at>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/mtd/ubi/vmt.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

--- a/drivers/mtd/ubi/vmt.c
+++ b/drivers/mtd/ubi/vmt.c
@@ -312,6 +312,12 @@ int ubi_create_volume(struct ubi_device
 			vol->last_eb_bytes = vol->usable_leb_size;
 	}
 
+	/* Make volume "available" before it becomes accessible via sysfs */
+	spin_lock(&ubi->volumes_lock);
+	ubi->volumes[vol_id] = vol;
+	ubi->vol_count += 1;
+	spin_unlock(&ubi->volumes_lock);
+
 	/* Register character device for the volume */
 	cdev_init(&vol->cdev, &ubi_vol_cdev_operations);
 	vol->cdev.owner = THIS_MODULE;
@@ -354,11 +360,6 @@ int ubi_create_volume(struct ubi_device
 	if (err)
 		goto out_sysfs;
 
-	spin_lock(&ubi->volumes_lock);
-	ubi->volumes[vol_id] = vol;
-	ubi->vol_count += 1;
-	spin_unlock(&ubi->volumes_lock);
-
 	ubi_volume_notify(ubi, vol, UBI_VOLUME_ADDED);
 	if (paranoid_check_volumes(ubi))
 		dbg_err("check failed while creating volume %d", vol_id);
@@ -379,6 +380,10 @@ out_sysfs:
 out_cdev:
 	cdev_del(&vol->cdev);
 out_mapping:
+	spin_lock(&ubi->volumes_lock);
+	ubi->volumes[vol_id] = NULL;
+	ubi->vol_count -= 1;
+	spin_unlock(&ubi->volumes_lock);
 	if (do_free)
 		kfree(vol->eba_tbl);
 out_acc: