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: >> http://lists.freebsd.org/mailman/htdig/freebsd-current/2004-August/033033.html > > > 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. -- NateReceived on Tue Mar 08 2005 - 13:46:14 UTC
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