--- Andrew Morton <akpm@xxxxxxxx> wrote: > On Thu, 30 Nov 2006 22:34:57 -0800 (PST) > Luben Tuikov <ltuikov@xxxxxxxxx> wrote: > > > --- Andrew Morton <akpm@xxxxxxxx> wrote: > > > On Wed, 29 Nov 2006 17:22:48 -0800 (PST) > > > Luben Tuikov <ltuikov@xxxxxxxxx> wrote: > > > > > > > Suppose reading sector 0 always reports an error, > > > > sense key HARDWARE ERROR. > > > > > > > > What I'm observing is that the request to read sector 0, > > > > reading partition information, is retried forever, ad infinitum. > > > > > > > > Does anyone have a patch to resolve this? (2.6.19-rc6) > > > > > > > > > > Please send a backtrace so we can see where the offending loop occurs. > > > > I posted a patch to linux-scsi > > hm. Does sending patches to linux-scsi get them applied? It might, I > don't know. Good question -- I don't know either. > > which resolves this issue: > > http://marc.theaimsgroup.com/?l=linux-scsi&m=116485834119885&w=2 > > That looks like it prevents the IO error. But why was an IO error causing > an infinite loop? What piece of code was initiating the retries? Here is what happens: sector 0 is broken -- the device cannot read the media at that location. The device properly returns a certain type of uncorrectable MEDIUM ERROR (ASC: UNRECOVERABLE READ ERR). SCSI Core loops around its retries (which this patch fixes) and eventually gives up and sends it for "completion". This is what happens when scsi_check_sense() returns NEEDS_RETRY to scsi_decide_disposition() to scsi_softirq(). The first chunk of the patch fixes this. We end up in scsi_io_completion(), where good_bytes = 0, and result = 0x08000002 (DRIVER SENSE and CHECK CONDITION). This statement in scsi_io_completion() causes the infinite retry loop: if (scsi_end_request(cmd, 1, good_bytes, !!result) == NULL) return; substitute to get: scsi_end_request(cmd, uptodate=1, uptodate bytes=0, retry=1) Yeah, but it doesn't make sense to call scsi_end_request() with uptodate=1 and uptodate bytes = 0. This causes the infinite retry, since the code tries to re-read the whole xfer size (0 bytes were uptodate and retry=1), from the bad media. That is, we want to set uptodate=1 iff there was at least 1 byte up to date. Else if nothing was read, uptodate bytes = 0, then we should pass uptodate = 0, uptodate_bytes = total xfer, to mean the whole xfer is not uptodate; and retry iff there was no error. (This is the very bottom of the function.) ... I know, I know, but that's what we've got. See this commit 03aba2f79594ca94d159c8bab454de9bcc385b76 as well. Luben - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
