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docs: mark nested AioContext locking as a legacy API

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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>
This commit is contained in:
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 This work is licensed under the terms of the GNU GPL, version 2 or later. See
the COPYING file in the top-level directory. 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 context is acquired no other thread can access it or run event loop iterations
in this AioContext. in this AioContext.
aio_context_acquire()/aio_context_release() calls may be nested. This Legacy code sometimes nests aio_context_acquire()/aio_context_release() calls.
means you can call them if you're not sure whether #2 applies. 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 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 AioContexts simultaneously. Therefore, it is only safe for code holding the