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block: Drain recursively with a single BDRV_POLL_WHILE()

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Anything can happen inside BDRV_POLL_WHILE(), including graph
changes that may interfere with its callers (e.g. child list iteration
in recursive callers of bdrv_do_drained_begin).

Switch to a single BDRV_POLL_WHILE() call for the whole subtree at the
end of bdrv_do_drained_begin() to avoid such effects. The recursion
happens now inside the loop condition. As the graph can only change
between bdrv_drain_poll() calls, but not inside of it, doing the
recursion here is safe.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2018-03-23 12:40:41 +01:00
parent 4c8158e359
commit fe4f0614ef
3 changed files with 52 additions and 22 deletions
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9
include/block/block.h
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@ -570,10 +570,13 @@ void bdrv_parent_drained_end(BlockDriverState *bs, BdrvChild *ignore);
/**
* bdrv_drain_poll:
*
* Poll for pending requests in @bs and its parents (except for
* @ignore_parent). This is part of bdrv_drained_begin.
* Poll for pending requests in @bs, its parents (except for @ignore_parent),
* and if @recursive is true its children as well.
*
* This is part of bdrv_drained_begin.
*/
bool bdrv_drain_poll(BlockDriverState *bs, BdrvChild *ignore_parent);
bool bdrv_drain_poll(BlockDriverState *bs, bool recursive,
BdrvChild *ignore_parent);
/**
* bdrv_drained_begin: