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由 Evgeny Yakovlev 提交于
The following commit commit 3ff2f67a Author: Evgeny Yakovlev <eyakovlev@virtuozzo.com> Date: Mon Jul 18 22:39:52 2016 +0300 block: ignore flush requests when storage is clean has introduced a regression. There is a problem that it is still possible for 2 requests to execute in non sequential fashion and sometimes this results in a deadlock when bdrv_drain_one/all are called for BDS with such stalled requests. 1. Current flushed_gen and flush_started_gen is 1. 2. Request 1 enters bdrv_co_flush to with write_gen 1 (i.e. the same as flushed_gen). It gets past flushed_gen != flush_started_gen and sets flush_started_gen to 1 (again, the same it was before). 3. Request 1 yields somewhere before exiting bdrv_co_flush 4. Request 2 enters bdrv_co_flush with write_gen 2. It gets past flushed_gen != flush_started_gen and sets flush_started_gen to 2. 5. Request 2 runs to completion and sets flushed_gen to 2 6. Request 1 is resumed, runs to completion and sets flushed_gen to 1. However flush_started_gen is now 2. From here on out flushed_gen is always != to flush_started_gen and all further requests will wait on flush_queue. This change replaces flush_started_gen with an explicitly tracked active flush request. Signed-off-by: NEvgeny Yakovlev <eyakovlev@virtuozzo.com> Signed-off-by: NDenis V. Lunev <den@openvz.org> Message-id: 1471457214-3994-2-git-send-email-den@openvz.org CC: Stefan Hajnoczi <stefanha@redhat.com> CC: Fam Zheng <famz@redhat.com> CC: Kevin Wolf <kwolf@redhat.com> CC: Max Reitz <mreitz@redhat.com> Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
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