Commit d02d8dde authored by Stefan Hajnoczi's avatar Stefan Hajnoczi
Browse files

docs: mark nested AioContext locking as a legacy API 



See the patch for why nested AioContext locking is no longer allowed.

Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Message-id: 20171207201320.19284-3-stefanha@redhat.com
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent bd6458e4

docs/devel/multiple-iothreads.txt

+4 −3
Original line number Diff line number Diff line 
Copyright (c) 2014 Red Hat Inc.

Copyright (c) 2014-2017 Red Hat Inc.



This work is licensed under the terms of the GNU GPL, version 2 or later.  See

the COPYING file in the top-level directory.
@@ -92,8 +92,9 @@ aio_context_acquire()/aio_context_release() for mutual exclusion. Once the 
context is acquired no other thread can access it or run event loop iterations

in this AioContext.



aio_context_acquire()/aio_context_release() calls may be nested.  This

means you can call them if you're not sure whether #2 applies.

Legacy code sometimes nests aio_context_acquire()/aio_context_release() calls.

Do not use nesting anymore, it is incompatible with the BDRV_POLL_WHILE() macro

used in the block layer and can lead to hangs.



There is currently no lock ordering rule if a thread needs to acquire multiple

AioContexts simultaneously.  Therefore, it is only safe for code holding the