On Tue, 4 Aug 2009, Lev A. Melnikovsky wrote: > Hello, > > I was advised to move this thread [ http://marc.info/?t=124916632000003&r=1&w=2 ] > to the linux-scsi mailing list. In my opinion the original problem > descriptions can be considered as a follow-up to a year old thread on > "JMicron JM20337 USB-SATA data corruption bugfix" [ http://marc.info/?l=linux-kernel&m=121653150327283&w=2 ]. > The JMicron bridge is connected to a SATA disk with genuine errors (bad > sectors, just in case: I am not going to use it but to recover some data > from it). Unfortunately when a bad block is read no error is returned, > instead a caller is blocked indefinitely (at least for two hours or until > the USB cable is removed). The system log is filled with repetitive > > sd 3:0:0:0: [sdf] Sense Key : 0x0 [current] > sd 3:0:0:0: [sdf] ASC=0x0 ASCQ=0x0 > > Alan Stern has suggested that this should be fixed as following: > > AS> Tell them that scsi_end_request() mustn't call scsi_requeue_command() > AS> if bytes == 0. > > Is this the right thing to do? To explain a little farther: The JMicron USB-SATA bridge has a nasty habit of not reporting errors correctly. It provides Check Condition status but SK, ASC, and ASCQ are all zero. In this case we're talking about read errors. This combination of codes causes scsi_end_request() to requeue the command, thereby resetting the block layer's cancellation timer. However if bytes == 0 then no forward progress was made in executing the command, so the retry fails at exactly the same spot as before and the system keeps retrying indefinitely. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
