Starting with the next-20100927 tag of linux-next I saw this error while booting ia64: Unable to handle kernel NULL pointer dereference (address 0000000000000020) usb-stor-scan[5915]: Oops 8813272891392 [1] Modules linked in: dm_mod usb_storage sg container button usbhid uhci_hcd ehci_hcd usbcore fan processor thermal thermal_sys Pid: 5915, CPU 0, comm: usb-stor-scan psr : 00001010085a6010 ifs : 8000000000000894 ip : [<a00000010012a630>] Not tainted (2.6.36-rc5-generic-smp-next-20100927) ip is at mempool_alloc+0x70/0x200 The problem was that "page_pool" was NULL, but blk_queue_bounce() had decided to use it! The code in mm/bounce.c looks quite fragile here as there are several places where page_pool is used, but it is only initialized inside #ifdef CONFIG_HIGHMEM (which is not set on ia64). Reverting this patch so that the old rules for setting q->limits.bounce_pfn are used cures the immediate problem. But I think there must be some deeper issues involved. I think that reverting means that I take the fast exit from blk_queue_bounce(): if (queue_bounce_pfn(q) >= blk_max_pfn) return; which is probably just avoiding the problem, rather than doing the right thing. -Tony -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
