On 05/08/2013 04:26 PM, Pekka Enberg wrote: > On Wed, May 8, 2013 at 2:58 PM, Glauber Costa <glom...@parallels.com> wrote: >> My first guess is that it hit a NULL cache. Being a NULL pointer >> dereference, the thing among all that has the biggest chances of being >> NULL and accessed unconditionally is the cache pointer itself. >> >> Due to the size being too big. But if that were the case, he would have >> hit the WARN_ON recently introduced: >> >> if (WARN_ON_ONCE(size > KMALLOC_MAX_SIZE)) >> return NULL; >> >> >> Is this WARN hit ? > > I doubt it: > > [ 0.000000] r7 : 00000000 r6 : 600001d3 r5 : 00000000 r4 : 00008000 > [ 0.000000] r3 : 00000050 r2 : c06ec000 r1 : c06f77c8 r0 : c00eda9c > > [ 0.000000] [<c00edab4>] (kmem_cache_alloc_trace+0x50/0x178) from > [<c0086958>] (alloc_desc+0x24/0xb4) > > It's the kzalloc_node() in kernel/irq/irqdesc.c::alloc_desc() and > AFAICT based on r4 it's a 32 KB allocation. It's more likely that > KMALLOC_SHIFT_HIGH is less than 25 and because kmalloc_index() doesn't > respect it, we return a pointer to an uninitialized kmalloc cache. >
Exactly, but then the index is calculated from the size. If we are allocating with a size that would lead to an invalid index, we should WARN. If this is not happening, that WARN is really really badly placed. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
