On Mon, Feb 11, 2013 at 02:52:36PM +0000, Mel Gorman wrote: > A user reported the following oops when a backup process read > /proc/kcore. > > BUG: unable to handle kernel paging request at ffffbb00ff33b000 > IP: [<ffffffff8103157e>] kern_addr_valid+0xbe/0x110 > PGD 0 > Oops: 0000 [#1] SMP > CPU 6 > Modules linked in: af_packet nfs lockd fscache auth_rpcgss nfs_acl sunrpc 8021q garp stp llc cpufreq_conservative cpufreq_userspace cpufreq_powersave acpi_cpufreq mperf microcode fuse nls_iso8859_1 nls_cp437 vfat fat loop dm_mod ioatdma ipv6 ipv6_lib igb dca i7core_edac edac_core i2c_i801 i2c_core cdc_ether usbnet bnx2 mii iTCO_wdt iTCO_vendor_support shpchp rtc_cmos pci_hotplug tpm_tis sg tpm pcspkr tpm_bios serio_raw button ext3 jbd mbcache uhci_hcd ehci_hcd usbcore sd_mod crc_t10dif usb_common processor thermal_sys hwmon scsi_dh_emc scsi_dh_rdac scsi_dh_alua scsi_dh_hp_sw scsi_dh ata_generic ata_piix libata megaraid_sas scsi_mod > > Pid: 16196, comm: Hibackp Not tainted 3.0.13-0.27-default #1 IBM System x3550 M3 -[7944 K3G]-/94Y7614 > RIP: 0010:[<ffffffff8103157e>] [<ffffffff8103157e>] kern_addr_valid+0xbe/0x110 > RSP: 0018:ffff88094165fe80 EFLAGS: 00010246 > RAX: 00003300ff33b000 RBX: ffff880100000000 RCX: 0000000000000000 > RDX: 0000000100000000 RSI: ffff880000000000 RDI: ff32b300ff33b400 > RBP: 0000000000001000 R08: 00003ffffffff000 R09: 0000000000000000 > R10: 22302e31223d6e6f R11: 0000000000000246 R12: 0000000000001000 > R13: 0000000000003000 R14: 0000000000571be0 R15: ffff88094165ff50 > FS: 00007ff152d33700(0000) GS:ffff88097f2c0000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b > CR2: ffffbb00ff33b000 CR3: 00000009405a3000 CR4: 00000000000006e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > Process Hibackp (pid: 16196, threadinfo ffff88094165e000, task ffff8808eb9ba600) > Stack: > ffffffff811b8aaa 0000000000004000 ffff880943fea480 ffff8808ef2bae50 > ffff880943d32980 fffffffffffffffb ffff8808ef2bae40 ffff88094165ff50 > 0000000000004000 000000000056ebe0 ffffffff811ad847 000000000056ebe0 > Call Trace: > [<ffffffff811b8aaa>] read_kcore+0x17a/0x370 > [<ffffffff811ad847>] proc_reg_read+0x77/0xc0 > [<ffffffff81151687>] vfs_read+0xc7/0x130 > [<ffffffff811517f3>] sys_read+0x53/0xa0 > [<ffffffff81449692>] system_call_fastpath+0x16/0x1b > > Investigation determined that the bug triggered when reading system RAM > at the 4G mark. On this system, that was the first address using 1G pages > for the virt->phys direct mapping so the PUD is pointing to a physical > address, not a PMD page. The problem is that the page table walker in > kern_addr_valid() is not checking pud_large() and treats the physical > address as if it was a PMD. If it happens to look like pmd_none then it'll > silently fail, probably returning zeros instead of real data. If the data > happens to look like a present PMD though, it will be walked resulting in > the oops above. This patch adds the necessary pud_large() check. > > Unfortunately the problem was not readily reproducible and now they are > running the backup program without accessing /proc/kcore so the patch has > not been validated but I think it makes sense. If reviewers agree then it > should also be included in -stable back as far as 3.0-stable. > > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Mel Gorman <mgorman@xxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> Agreed also on the backporting to -stable as far as possible. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>