[Bug 13399] kernel crash SONY DVD-ROM with cd

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http://bugzilla.kernel.org/show_bug.cgi?id=13399





--- Comment #20 from Borislav Petkov <bbpetkov@yahoo.de>  2009-06-13 16:29:05 ---
Hi Bart,

thanks for analyzing this.

I'm staring at the ATA_DRQ == 0 part in cdrom_newpc_intr:

                } else if (!blk_pc_request(rq)) {
                        ide_cd_request_sense_fixup(drive, cmd);
                        /* complain if we still have data left to transfer */
                        uptodate = cmd->nleft ? 0 : 1;
                        if (uptodate == 0)
                                rq->cmd_flags |= REQ_FAILED;
                }
                goto out_end;
        }

so, in our case ide_cd_error_cmd() kills the rq prematurely and that's
why ide_complete_rq() oopses later. And this is caused by uptodate ==
0. Now, here's how the ATA spec (d1532v1r4b-ATA-ATAPI-7) describes the
semantics of clearing of the DRQ bit by the drive:

"
5.14.5.5 DRQ (Data request)

...

The DRQ bit shall be cleared to zero by the device:
         1) when the last word of the data transfer occurs;
         2) when the last word of the command packet transfer occurs for a
PACKET command.
"

now there's a subtlety here wrt to what am I to do as an IRQ handler
when my drive clears the DRQ bit: do I _drain_ the last bytes remaining
(in our case 2) or do I fail the rq straightaway. I'm pretty sure
cmd->nleft is 2 in our case so I think that it might be only right to
drain the device first, i.e. do

    uptodate = (cmd->nleft - thislen) ? 0 : 1;

and then later ide_pio_bytes() before completing the rq properly. Hmm?

And yes, this is against spec since the following sentence states that
the data can be drained only "... via DMA mode if DMARQ and DMACK- are
asserted and BSY is set to one." but we should give it a try...

Ideas? Opinions?

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