Il 27/05/2014 12:59, James Bottomley ha scritto:
On Tue, 2014-05-27 at 12:47 +0200, Paolo Bonzini wrote:
Il 27/05/2014 12:21, James Bottomley ha scritto:
I could also see us one day extending the TMF capability to abort any
running command, which would make even an assertion of block timed out
or completed invalid.
Actually the assertion would remain valid, and that's exactly what Bart
wants to document with this assertion.
No, it wouldn't: if we abort a running command by definition the command
hadn't timed out and might not be completed. This is required by TMF
handling because now you have an abort racing with a completion. Either
the command completes normally because it misses the abort or the abort
gets to it and its returned status is set to TASK_ABORTED. That's the
only way you can tell if the abort was successful or not.
If you're thinking we would tell block to ignore returning commands
before issuing the abort, we'd never be able to tell if the abort were
successful, so we have to allow the race to collect the status.
You could use a different mechanism than a softirq to tell the abort
were successful, for example by overriding scsi_done. But with respect
to the block layer, the mechanics of avoiding the race and double-free
would probably be the same.
Paolo
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