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
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