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[PATCH] ubi: fastmap: Cancel work upon detach

Ben Hutchings pointed out that 29b7a6fa1ec0 ("ubi: fastmap: Don't flush
fastmap work on detach") does not really fix the problem, it just
reduces the risk to hit the race window where fastmap work races against
free()'ing ubi->volumes[].

The correct approach is making sure that no more fastmap work is in
progress before we free ubi data structures.
So we cancel fastmap work right after the ubi background thread is
By setting ubi->thread_enabled to zero we make sure that no further work
tries to wake the thread.

Fixes: 29b7a6fa1ec0 ("ubi: fastmap: Don't flush fastmap work on detach")
Fixes: 74cdaf24004a ("UBI: Fastmap: Fix memory leaks while closing the WL sub-system")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Ben Hutchings <ben.hutchings@xxxxxxxxxxxxxxx>
Cc: Martin Townsend <mtownsend1973@xxxxxxxxx>

Signed-off-by: Richard Weinberger <richard@xxxxxx>
 drivers/mtd/ubi/build.c | 3 +++
 drivers/mtd/ubi/wl.c    | 4 +---
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index 6326a02e4568..0cf3356424cd 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -1100,6 +1100,9 @@ int ubi_detach_mtd_dev(int ubi_num, int anyway)
 	if (ubi->bgt_thread)
+	cancel_work_sync(&ubi->fm_work);
diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index 3cc302924899..6bbb968fe9da 100644
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -1505,6 +1505,7 @@ int ubi_thread(void *u)
 	dbg_wl("background thread \"%s\" is killed", ubi->bgt_name);
+	ubi->thread_enabled = 0;
 	return 0;
@@ -1514,9 +1515,6 @@ int ubi_thread(void *u)
 static void shutdown_work(struct ubi_device *ubi)
-	flush_work(&ubi->fm_work);
 	while (!list_empty(&ubi->works)) {
 		struct ubi_work *wrk;