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| author | Stefan Hajnoczi <stefanha@redhat.com> | 2017-12-07 20:13:16 +0000 |
|---|---|---|
| committer | Stefan Hajnoczi <stefanha@redhat.com> | 2017-12-19 10:25:09 +0000 |
| commit | d02d8dde0c0fe3d77a31046e104a55f2e6c50bf6 (patch) | |
| tree | f4c0189984258f0a4025b91959bde8be09c00106 | |
| parent | bd6458e410c1e7d2912357aeb399fe7d8ee9f9a3 (diff) | |
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>
| -rw-r--r-- | docs/devel/multiple-iothreads.txt | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/docs/devel/multiple-iothreads.txt b/docs/devel/multiple-iothreads.txt index e4d340bbb7..4f9012d154 100644 --- a/docs/devel/multiple-iothreads.txt +++ b/docs/devel/multiple-iothreads.txt @@ -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 |