Patch "bcache: check ca->alloc_thread initialized before wake up it" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

    bcache: check ca->alloc_thread initialized before wake up it

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
bcache-check-ca-alloc_thread-initialized-before-wake-up-it.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Coly Li <[email protected]>
Date: Fri, 13 Oct 2017 16:35:29 -0700
Subject: bcache: check ca->alloc_thread initialized before wake up it

From: Coly Li <[email protected]>

commit 91af8300d9c1d7c6b6a2fd754109e08d4798b8d8 upstream.

In bcache code, sysfs entries are created before all resources get allocated, e.g. allocation thread of a cache set.

There is posibility for NULL pointer deference if a resource is accessed but which is not initialized yet. Indeed Jorg Bornschein catches one on cache set allocation thread and gets a kernel oops.

The reason for this bug is, when bch_bucket_alloc() is called during cache set registration and attaching, ca->alloc_thread is not properly allocated and initialized yet, call wake_up_process() on ca->alloc_thread triggers NULL pointer deference failure. A simple and fast fix is, before waking up ca->alloc_thread, checking whether it is allocated, and only wake up ca->alloc_thread when it is not NULL.

---
 drivers/md/bcache/alloc.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -404,7 +404,8 @@ long bch_bucket_alloc(struct cache *ca,
 
 	finish_wait(&ca->set->bucket_wait, &w);
 out:
-	wake_up_process(ca->alloc_thread);
+	if (ca->alloc_thread)
+		wake_up_process(ca->alloc_thread);
 
 	trace_bcache_alloc(ca, reserve);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/bcache-only-permit-to-recovery-read-error-when-cache-device-is-clean.patch queue-4.9/bcache-check-ca-alloc_thread-initialized-before-wake-up-it.patch