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authorTejun Heo <tj@kernel.org>2012-09-05 08:16:32 +0200
committerTejun Heo <tj@kernel.org>2012-09-06 01:10:15 +0200
commitec58815ab0409a921a7c9744eb4ca44866b14d71 (patch)
tree228f1fb9035cc0b3f60fc14707614305608c96d1 /init
parentworkqueue: move WORKER_REBIND clearing in rebind_workers() to the end of the ... (diff)
downloadlinux-ec58815ab0409a921a7c9744eb4ca44866b14d71.tar.xz
linux-ec58815ab0409a921a7c9744eb4ca44866b14d71.zip
workqueue: fix possible deadlock in idle worker rebinding
Currently, rebind_workers() and idle_worker_rebind() are two-way interlocked. rebind_workers() waits for idle workers to finish rebinding and rebound idle workers wait for rebind_workers() to finish rebinding busy workers before proceeding. Unfortunately, this isn't enough. The second wait from idle workers is implemented as follows. wait_event(gcwq->rebind_hold, !(worker->flags & WORKER_REBIND)); rebind_workers() clears WORKER_REBIND, wakes up the idle workers and then returns. If CPU hotplug cycle happens again before one of the idle workers finishes the above wait_event(), rebind_workers() will repeat the first part of the handshake - set WORKER_REBIND again and wait for the idle worker to finish rebinding - and this leads to deadlock because the idle worker would be waiting for WORKER_REBIND to clear. This is fixed by adding another interlocking step at the end - rebind_workers() now waits for all the idle workers to finish the above WORKER_REBIND wait before returning. This ensures that all rebinding steps are complete on all idle workers before the next hotplug cycle can happen. This problem was diagnosed by Lai Jiangshan who also posted a patch to fix the issue, upon which this patch is based. This is the minimal fix and further patches are scheduled for the next merge window to simplify the CPU hotplug path. Signed-off-by: Tejun Heo <tj@kernel.org> Original-patch-by: Lai Jiangshan <laijs@cn.fujitsu.com> LKML-Reference: <1346516916-1991-3-git-send-email-laijs@cn.fujitsu.com>
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