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docs: mark nested AioContext locking as a legacy API 

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

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20171207201320.19284-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
master
Stefan Hajnoczi 2017-12-07 20:13:16 +00:00
parent bd6458e410
commit d02d8dde0c
1 changed files with 4 additions and 3 deletions
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7
docs/devel/multiple-iothreads.txt
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@ -1,4 +1,4 @@
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