Red Hat Bugzilla – Bug 783313
Possible race between read-ahead and write
Last modified: 2013-07-24 13:49:46 EDT
Description of problem:
Currently, it's possible for a write to occur while a read-ahead is in progress, and nothing is done to interrupt or cancel that read-ahead. As a result, a user read which is fully subsequent to that write (even if it's O_SYNC) could still get the read-ahead data which is now stale.
It's a race, found by inspection, so it's probably pretty hard to hit (hasn't been observed in practice except by stopping things in a debugger). It might be possible to construct a log-tailing test case, as that would leave one process reading just behind where another was writing on the same client. Meanwhile, since read-ahead is just a performance optimization, it should be safe to disable it when the risk can be anticipated.
CHANGE: http://review.gluster.com/2666 (Fix race between read-ahead and write.) merged in master by Anand Avati (firstname.lastname@example.org)
This bug was filed as part of the review and was not able to reproduce it. So moving this to verified.