linux-kernel - [PATCH 3.13 80/99] block: __elv_next_request() shouldnt call into the elevator if bypassing

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20140220235120.525944079@linuxfoundation.org>
Date:	Thu, 20 Feb 2014 15:53:15 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Frank Mayhar <fmayhar@...gle.com>,
	Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 3.13 80/99] block: __elv_next_request() shouldnt call into the elevator if bypassing

3.13-stable review patch.  If anyone has any objections, please let me know.

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

From: Tejun Heo <tj@...nel.org>

commit 556ee818c06f37b2e583af0363e6b16d0e0270de upstream.

request_queue bypassing is used to suppress higher-level function of a
request_queue so that they can be switched, reconfigured and shut
down.  A request_queue does the followings while bypassing.

* bypasses elevator and io_cq association and queues requests directly
  to the FIFO dispatch queue.

* bypasses block cgroup request_list lookup and always uses the root
  request_list.

Once confirmed to be bypassing, specific elevator and block cgroup
policy implementations can assume that nothing is in flight for them
and perform various operations which would be dangerous otherwise.

Such confirmation is acheived by short-circuiting all new requests
directly to the dispatch queue and waiting for all the requests which
were issued before to finish.  Unfortunately, while the request
allocating and draining sides were properly handled, we forgot to
actually plug the request dispatch path.  Even after bypassing mode is
confirmed, if the attached driver tries to fetch a request and the
dispatch queue is empty, __elv_next_request() would invoke the current
elevator's elevator_dispatch_fn() callback.  As all in-flight requests
were drained, the elevator wouldn't contain any request but once
bypass is confirmed we don't even know whether the elevator is even
there.  It might be in the process of being switched and half torn
down.

Frank Mayhar reports that this actually happened while switching
elevators, leading to an oops.

Let's fix it by making __elv_next_request() avoid invoking the
elevator_dispatch_fn() callback if the queue is bypassing.  It already
avoids invoking the callback if the queue is dying.  As a dying queue
is guaranteed to be bypassing, we can simply replace blk_queue_dying()
check with blk_queue_bypass().

Reported-by: Frank Mayhar <fmayhar@...gle.com>
References: http://lkml.kernel.org/g/1390319905.20232.38.camel@bobble.lax.corp.google.com
Tested-by: Frank Mayhar <fmayhar@...gle.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 block/blk.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/block/blk.h
+++ b/block/blk.h
@@ -113,7 +113,7 @@ static inline struct request *__elv_next
 			q->flush_queue_delayed = 1;
 			return NULL;
 		}
-		if (unlikely(blk_queue_dying(q)) ||
+		if (unlikely(blk_queue_bypass(q)) ||
 		    !q->elevator->type->ops.elevator_dispatch_fn(q, 0))
 			return NULL;
 	}

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/