Messages in this thread Patch in this message | | | Subject | Re: 2.6.24-rc3-mm1: I/O error, system hangs | From | James Bottomley <> | Date | Sat, 24 Nov 2007 19:44:13 +0200 |
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Probing intermittent failures in Domain Validation, even with the fixes applied leads me to the conclusion that there are further problems with this commit:
commit fc5eb4facedbd6d7117905e775cee1975f894e79 Author: Hannes Reinecke <hare@suse.de> Date: Tue Nov 6 09:23:40 2007 +0100
[SCSI] Do not requeue requests if REQ_FAILFAST is set
The essence of the problems is that you're causing REQ_FAILFAST to terminate commands with error on requeuing conditions, some of which are relatively common on most SCSI devices. While this may be the correct behaviour for multi-path, it's certainly wrong for the previously understood meaning of REQ_FAILFAST, which was don't retry on error, which is why domain validation and other applications use it to control error handling, but don't expect to get failures for a simple requeue are now spitting errors.
I honestly can't see that, even for the multi-path case, returning an error when we're over queue depth is the correct thing to do (it may not matter to something like a symmetrix, but an array that has a non-zero cost associated with a path change, like a CPQ HSV or the AVT controllers, will show fairly large slow downs if you do this). Even if this is the desired behaviour (and I think that's a policy issue), DID_NO_CONNECT is almost certainly the wrong error to be sending back.
This patch fixes up domain validation to work again correctly, however, I really think it's just a bandaid. Do you want to rethink the above commit?
James
Index: BUILD-2.6/drivers/scsi/scsi_lib.c =================================================================== --- BUILD-2.6.orig/drivers/scsi/scsi_lib.c 2007-11-24 11:25:20.000000000 -0600 +++ BUILD-2.6/drivers/scsi/scsi_lib.c 2007-11-24 11:26:22.000000000 -0600 @@ -1552,7 +1552,8 @@ static void scsi_request_fn(struct reque break; if (!scsi_dev_queue_ready(q, sdev)) { - if (req->cmd_flags & REQ_FAILFAST) { + if ((req->cmd_flags & REQ_FAILFAST) && + !(req->cmd_flags & REQ_PREEMPT)) { scsi_kill_request(req, q); continue; }
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