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throttle: Fix crash on reopen
The throttle block filter can be reopened, and with this it is possible to change the throttle group that the filter belongs to. The way the code does that is the following: - On throttle_reopen_prepare(): create a new ThrottleGroupMember and attach it to the new throttle group. - On throttle_reopen_commit(): detach the old ThrottleGroupMember, delete it and replace it with the new one. The problem with this is that by replacing the ThrottleGroupMember the previous value of io_limits_disabled is lost, causing an assertion failure in throttle_co_drain_end(). This problem can be reproduced by reopening a throttle node: $QEMU -monitor stdio -object throttle-group,id=tg0,x-iops-total=1000 \ -blockdev node-name=hd0,driver=qcow2,file.driver=file,file.filename=hd.qcow2 \ -blockdev node-name=root,driver=throttle,throttle-group=tg0,file=hd0,read-only=on (qemu) block_stream root block/throttle.c:214: throttle_co_drain_end: Assertion `tgm->io_limits_disabled' failed. Since we only want to change the throttle group on reopen there's no need to create a ThrottleGroupMember and discard the old one. It's easier if we simply detach it from its current group and attach it to the new one. Signed-off-by: Alberto Garcia <firstname.lastname@example.org> Message-id: email@example.com Signed-off-by: Max Reitz <firstname.lastname@example.org>
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