The problem was indeed never reported upstream but it does in fact manifest as a null pointer dereference, and happens in a discontiguous memory context on m68k. I'm uncertain as to whether I had tracked the exact source of the null pointer, I need to check my notes on this. Reverting the commit in question makes SLUB behave as though NUMA was defined, so this all checks out. Apologies for not escalating this beyond m68k, and thanks to Geert for spotting the connection. Cheers, Michael On Wed, Apr 20, 2011 at 7:48 PM, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > On Tue, Apr 19, 2011 at 23:29, James Bottomley > <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote: >> Slub makes assumptions about page_to_nid() which are violated by >> DISCONTIGMEM and !NUMA. This violation results in a panic because >> page_to_nid() can be non-zero for pages in the discontiguous ranges and >> this leads to a null return by get_node(). The assertion by the >> maintainer is that DISCONTIGMEM should only be allowed when NUMA is also >> defined. However, at least six architectures: alpha, ia64, m32r, m68k, >> mips, parisc violate this. The panic is a regression against slab, so >> just mark slub broken in the problem configuration to prevent users >> reporting these panics. > > How does the problem manifest itself? We're having a problem on m68k, which > seems to go away when switching from SLUB to SLAB, or when reverting a commit > in [2] (probably this was never reported upstream). > > References: > [1] http://www.mail-archive.com/linux-m68k@xxxxxxxxxxxxxxx/msg02812.html > [2] http://www.spinics.net/lists/linux-m68k/msg03401.html > >> Cc: stable@xxxxxxxxxx >> Signed-off-by: James Bottomley <James.Bottomley@xxxxxxx> >> >> --- >> >> diff --git a/init/Kconfig b/init/Kconfig >> index 56240e7..a7ad8fb 100644 >> --- a/init/Kconfig >> +++ b/init/Kconfig >> @@ -1226,6 +1226,7 @@ config SLAB >> per cpu and per node queues. >> >> config SLUB >> + depends on BROKEN || NUMA || !DISCONTIGMEM >> bool "SLUB (Unqueued Allocator)" >> help >> SLUB is a slab allocator that minimizes cache line usage > > Gr{oetje,eeting}s, > > Geert > > -- > Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx > > In personal conversations with technical people, I call myself a hacker. But > when I'm talking to journalists I just say "programmer" or something like that. > -- Linus Torvalds > -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
