CVE-2021-47646

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> Revert "Revert "block, bfq: honor already-setup queue merges""<br /> <br /> A crash [1] happened to be triggered in conjunction with commit<br /> 2d52c58b9c9b ("block, bfq: honor already-setup queue merges"). The<br /> latter was then reverted by commit ebc69e897e17 ("Revert "block, bfq:<br /> honor already-setup queue merges""). Yet, the reverted commit was not<br /> the one introducing the bug. In fact, it actually triggered a UAF<br /> introduced by a different commit, and now fixed by commit d29bd41428cf<br /> ("block, bfq: reset last_bfqq_created on group change").<br /> <br /> So, there is no point in keeping commit 2d52c58b9c9b ("block, bfq:<br /> honor already-setup queue merges") out. This commit restores it.<br /> <br /> [1] https://bugzilla.kernel.org/show_bug.cgi?id=214503