DragonFly kernel List (threaded) for 2003-11
Re: ATA errors.
::I found that there's a place where ATA driver silently falls back to
::BIOSPIO mode even when bootverbose is true. In ad_start(), if the
::call to ata_dmaalloc fails, adp->device->mode is set to ATA_PIO, but
::there's no ata_prtdev() around there, that's why we don't see any
::`fallback' messages. I'm not sure why ata_dmaalloc() failed.
::Anyway, attached is a patch to add ata_prtdev(), and add a knob
: Ah, Excellent. It's because it is using M_NOWAIT and the allocation
: can fail if kernel_map is locked. This is just bad algorithm design
: because allocations with M_NOWAIT can fail even on FreeBSD-4.x boxes.
: I will encapsulate the dmatab freeing code and make it unconditional.
Damn. This is not going to be as easy to fix as I thought... the ATA
code is seriously broken. It uses M_NOWAIT all over the place for
things that just have no business being M_NOWAIT.
DragonFly will generate NULL returns for M_NOWAIT requests more often
then FreeBSD-4.x due to blockages on kernel_map (FreeBSD-4.x has kmem_mem
for allocations when kernel_map is locked).