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authorKrishnan Parthasarathi <>2013-04-15 15:56:57 +0530
committerVijay Bellur <>2013-04-17 05:48:50 -0700
commit92729add67e2e7b8c7589c2dfab0bde071a7faf2 (patch)
tree4e8c2d48de34938a71abd320402e98e1588aee30 /
parent47c118e22d9d6fb6662fe96841ed4fe3089739b5 (diff)
glusterd: big lock - a coarse-grained locking to prevent racesv3.4.0alpha3
There are primarily three lists that are part of glusterd process, that are concurrently accessed. Namely, priv->volumes, priv->peers and volinfo->bricks_list. Big-lock approach ----------------- WHAT IS IT? Big lock is a coarse-grained lock which protects all three lists, mentioned above, from racy access. HOW DOES IT WORK? At any given point in time, glusterd's thread(s) are in execution _iff_ there is a preceding, inbound network event. Of course, the sigwaiter thread and timer thread are exceptions. A network event is an external trigger to glusterd, via the epoll thread, in the form of POLLIN and POLLERR. As long as we take the big-lock at all such entry points and yield it when we are done, we are guaranteed that all the network events, accessing the global lists, are serialised. This amounts to holding the big lock at - all the handlers of all the actors in glusterd. (POLLIN) - all the cbks in glusterd. (POLLIN) - rpc_notify (DISCONNECT event), if we access/modify one of the three lists. (POLLERR) In the case of synctask'ized volume operations, we must remember that, if we held the big lock for the entire duration of the handler, we may block other non-synctask rpc actors from executing. For eg, volume-start would block in PMAP SIGNIN, if done incorrectly. To prevent this, we need to yield the big lock, when we yield the synctask, and reacquire on waking up of the synctask. BUG: 948686 Change-Id: I429832f1fed67bcac0813403d58346558a403ce9 Signed-off-by: Krishnan Parthasarathi <> Reviewed-on: Tested-by: Gluster Build System <> Reviewed-by: Vijay Bellur <>
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