[v2,2/6] docs: mark nested AioContext locking as a legacy API

Message ID 20171207201320.19284-3-stefanha@redhat.com
State New
Headers show
Series
  • block: avoid recursive AioContext acquire in bdrv_inactivate_all()
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Commit Message

Stefan Hajnoczi Dec. 7, 2017, 8:13 p.m.
See the patch for why nested AioContext locking is no longer allowed.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 docs/devel/multiple-iothreads.txt | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Comments

Eric Blake Dec. 7, 2017, 10:34 p.m. | #1
On 12/07/2017 02:13 PM, Stefan Hajnoczi wrote:
> See the patch for why nested AioContext locking is no longer allowed.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  docs/devel/multiple-iothreads.txt | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

Patch

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