patch: fix ata panic with Thinkpad CD and DVD drives

Nate Lawson nate at
Tue Mar 8 06:50:34 PST 2005

Søren Schmidt wrote:
> Nate Lawson wrote:
>> If you've been having "memory modified after free" panics on -current 
>> and have a Thinkpad, the attached patch should fix things for you.  A 
>> quick check of RELENG_5 indicates that the bug is probably there also 
>> but I haven't tested for it there.
>> The bug is triggered by timeouts in the ata_getparam() probe path.  
>> The ata_timeout() fires and ata_end_transaction() is called to get the 
>> status.  However, it continues down into ata_pio_read() even though 
>> there is no data available since we had a timeout, not read 
>> completion.    ata_pio_read() reads 512 bytes of probably bogus data.  
>> The important problem is that it also advances donecount.  On 
>> subsequent timeouts (note there are 4 below), donecount advances into 
>> unallocated memory and so subsequent ata_pio_read() calls overwrite 
>> 512 bytes of someone else's memory.
>> The fix is to exit immediately if ATA_R_TIMEOUT is set after reading 
>> the status in ata_end_transaction().  It shouldn't go into 
>> ata_pio_read() if there was a timeout.  The patch does this.
>> However, it only handles PIO timeouts since I wasn't sure the best way 
>> to proceed for unwinding DMA state and the like for the other cases. 
>> This is enough to fix the overwrite and subsequent panic on my 
>> systems.  I've run heavy IO stress and DVD accesses for a while and no 
>> further panics.
>> While looking into this, I found another potential problem.  In one 
>> reinjection case, donecount wasn't reset to 0.  The patch for 
>> ata-queue.c does this and I think it's necessary but don't hit this 
>> case in testing so I can't be sure.  Finally, there's one whitespace 
>> nit that helps with clarity.
>> These are similar bugs to one found back in August that had the same 
>> effect.  Here's the closest reference I could find in the mail 
>> archives for this:
> Just a note from here, these bugs are fixed in ATA mkIII so you could 
> just have gleaned the solution from there (or maybe you did :))

Nope, but I'm glad you can corroborate these fixes are correct.


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