* David Miller <davem@xxxxxxxxxxxxx> wrote: > From: Joerg Roedel <joerg.roedel@xxxxxxx> > Date: Tue, 14 Jul 2009 11:23:55 +0200 > > > On Tue, Jul 14, 2009 at 10:40:16AM +0900, FUJITA Tomonori wrote: > >> On Mon, 13 Jul 2009 20:56:21 -0400 > >> Robert Reif <reif@xxxxxxxxxxxxx> wrote: > >> > >> > The bad address is within the kernel so it looks like > >> > it's catching a real bug. > >> > > >> > cat kallsyms | grep f0007000 > >> > f0007000 T trapbase_cpu3 > >> > > >> > WARNING: at lib/dma-debug.c:873 check_for_illegal_area+0xc8/0x100() > >> > esp ffd7ba30: DMA-API: device driver maps memory from kernel text or > >> > rodata [addr=f0007000] [len=4096] > >> > Modules linked in: ext3 jbd sd_mod sun_esp esp_scsi scsi_transport_spi > >> > >> Ok, I looked at check_for_illegal_area() in dma-debug. > >> > >> What check_for_illegal_area() does looks bogus to me with some of I/O > >> remapping hardware. > > > > Can you be more specific about this one? > > check_for_illegal_area() should not depend on any hardware > > because all it does is checking the machine addresses to be > > mapped. > > The check can't work properly on sparc32. > > Sparc32 always maps the kernel to a fixed physical location, and > it therefore can execute in the identity mapping area of physical > memory like where all the free pages and kmalloc areas live > virtually. > > So if we free up some pages within the kernel image (because the > memory is unused, for exmple that's what's happening here with the > extra trap table pages on Robert's machine) we have pages in the > free page pool that are located right inside of the kernel text, > data, etc. > > We'll thus need a way to turn off these checks somehow. You could > also augment this check by seeing if there is a backing page, and > if so, whether it is PageReserved or not. That's just one idea. Hm, note, this sparc32 behavior might break certain aspects of lockdep as well, see kernel/lockdep.c::static_obj(). You could get spurious non-printing of 'trying to register non-static key'. I'm wondering why sparc32 frees from the middle of the kernel image. The way architectures generally do it is to put freeable pages into a separate section. That way it does not get mingled with the kernel core image area (which stays nicely continuous). Ingo -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
