Richard Sharpe wrote: > On Sun, Aug 17, 2008 at 10:48 PM, Mark Harvey <markh794 at gmail.com> wrote: >> From ea4d57fca07516c03980970cf90b937c45e3811e Mon Sep 17 00:00:00 2001 >> From: Mark Harvey <markh794 at gmail.com> >> Date: Mon, 18 Aug 2008 15:03:21 +1000 >> Subject: New backing store for ssc type devices. >> >> Uses a double-linked list header with each block of data. >> >> Implement basic fixed block READ_6 & WRITE_6 OP codes. >> >> Still along way to go. >> - Race condition on blk header between threads. > > Hmmm, why do you say there is a race here? Surely only one initiator > can access a tape at one time, and unless you have multiple threads > for the one tape, there should not be a problem here, unless I am > missing something? > It may be me that's missing something. I still have not got my head around the multi-threaded code. However I assume that 'multi-threaded' allows a worker thread to accept one SCSI op code. If the 2nd (or subsequent command) arrives during the update of the blk_header by the earlier thread, then there is a possibility of one thread using the blk_header belonging to the first thread and over writing each others data & header. e.g. writeA -> read blk_headerX (and start to copy/build new blk_headerY) writeB arrives before writeA has completed building blk_headerY Results is A & B writes will use the same blk_header (blk_headerX) information and over-write each others data. I am more then happy to be told I'm wrong. But I see some simple locking process during the period of 'read header -> update new header & save in SSC header'. Then allow actual write/read of any data process to complete outside the mutex/spinlock Cheers Mark -- To unsubscribe from this list: send the line "unsubscribe stgt" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html |