Hi, Today, after updating to Debian 8.4, I had the same problem (see below the extract from syslog). So, I reinstalled the previous package 3.16.7-ckt20-1+deb8u4 and everything back to the way it was before.
Syslog extrack Apr 3 22:04:45 hpcore2 kernel: [ 3754.417930] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 Apr 3 22:04:45 hpcore2 kernel: [ 3754.417982] IP: [<ffffffffa040bc3d>] radeon_fence_ref+0xd/0x50 [radeon] Apr 3 22:04:45 hpcore2 kernel: [ 3754.418053] PGD 0 Apr 3 22:04:45 hpcore2 kernel: [ 3754.418067] Oops: 0002 [#1] SMP Apr 3 22:04:45 hpcore2 kernel: [ 3754.418090] Modules linked in: bnep bluetooth 6lowpan_iphc snd_hrtimer snd_seq snd_seq_device cfg80211 rfkill binfmt_misc nfsd auth_rpcgss oid_registry nfs_acl nfs lockd fscache sunrpc usblp radeon ttm drm_kms_helper drm i2c_algo_bit pcspkr serio_raw iTCO_wdt iTCO_vendor_support evdev coretemp i2c_i801 i2c_core snd_hda_codec_realtek snd_hda_codec_hdmi snd_hda_codec_generic snd_hda_intel snd_hda_controller snd_hda_codec snd_hwdep snd_pcm snd_timer snd lpc_ich mfd_core shpchp soundcore button acpi_cpufreq processor thermal_sys loop fuse parport_pc ppdev lp parport autofs4 ext4 crc16 mbcache jbd2 usb_storage sg sd_mod crc_t10dif crct10dif_generic sr_mod cdrom crct10dif_common ata_generic psmouse ata_piix libata scsi_mod firewire_ohci r8169 firewire_core mii crc_itu_t ehci_pci uhci_hcd ehci_hcd usbcore usb_common Apr 3 22:04:45 hpcore2 kernel: [ 3754.418642] CPU: 0 PID: 697 Comm: Xorg Not tainted 3.16.0-4-amd64 #1 Debian 3.16.7-ckt25-1 Apr 3 22:04:45 hpcore2 kernel: [ 3754.418677] Hardware name: Hewlett-Packard HP Compaq dx2400 Microtower/2A73, BIOS 5.23 04/21/2008 Apr 3 22:04:45 hpcore2 kernel: [ 3754.418716] task: ffff88007a9db430 ti: ffff88007a9ec000 task.ti: ffff88007a9ec000 Apr 3 22:04:45 hpcore2 kernel: [ 3754.418746] RIP: 0010:[<ffffffffa040bc3d>] [<ffffffffa040bc3d>] radeon_fence_ref +0xd/0x50 [radeon] Apr 3 22:04:45 hpcore2 kernel: [ 3754.418796] RSP: 0018:ffff88007a9efb18 EFLAGS: 00010292 Apr 3 22:04:45 hpcore2 kernel: [ 3754.418820] RAX: 0000000000000000 RBX: ffff88007961d5f8 RCX: ffff88007961cd08 Apr 3 22:04:45 hpcore2 kernel: [ 3754.418849] RDX: 0000000000000001 RSI: 0000000000000000 RDI: 0000000000000000 Apr 3 22:04:45 hpcore2 kernel: [ 3754.418878] RBP: ffff88007961d550 R08: ffff88007961c000 R09: 0000000000000000 Apr 3 22:04:45 hpcore2 kernel: [ 3754.418907] R10: 0000000000000002 R11: ffffffffffffffec R12: 0000000000000020 Apr 3 22:04:45 hpcore2 kernel: [ 3754.418936] R13: ffff88007a9efbe0 R14: ffff88007a9efbb0 R15: ffff88007961d5f8 Apr 3 22:04:45 hpcore2 kernel: [ 3754.418966] FS: 00007f1092278980(0000) GS:ffff88007fc00000(0000) knlGS:0000000000000000 Apr 3 22:04:45 hpcore2 kernel: [ 3754.419001] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 Apr 3 22:04:45 hpcore2 kernel: [ 3754.419024] CR2: 0000000000000008 CR3: 000000007a993000 CR4: 00000000000007f0 Apr 3 22:04:45 hpcore2 kernel: [ 3754.419054] Stack: Apr 3 22:04:45 hpcore2 kernel: [ 3754.419064] ffffffffa046c0bc 00200000000c0000 0000f00000000100 ffff88007a9efcd0 Apr 3 22:04:45 hpcore2 kernel: [ 3754.419106] ffff88007961c000 ffff88007a9db430 ffff88007a9db430 00000000000002e0 Apr 3 22:04:45 hpcore2 kernel: [ 3754.419147] 0000000000000000 0000000000000000 0000000000000000 0000000000000000 Apr 3 22:04:45 hpcore2 kernel: [ 3754.419189] Call Trace: Apr 3 22:04:45 hpcore2 kernel: [ 3754.419217] [<ffffffffa046c0bc>] ? radeon_sa_bo_new+0x25c/0x460 [radeon] Apr 3 22:04:45 hpcore2 kernel: [ 3754.419259] [<ffffffffa0420f3e>] ? radeon_ib_get+0x2e/0xd0 [radeon] Apr 3 22:04:45 hpcore2 kernel: [ 3754.419301] [<ffffffffa042347c>] ? radeon_cs_ioctl+0x13c/0x730 [radeon] Apr 3 22:04:45 hpcore2 kernel: [ 3754.419340] [<ffffffffa03778b7>] ? drm_ioctl+0x1c7/0x5b0 [drm] Apr 3 22:04:45 hpcore2 kernel: [ 3754.419371] [<ffffffff81057311>] ? __do_page_fault+0x1d1/0x4f0 Apr 3 22:04:45 hpcore2 kernel: [ 3754.419407] [<ffffffffa03f0046>] ? radeon_drm_ioctl+0x46/0x80 [radeon] Apr 3 22:04:45 hpcore2 kernel: [ 3754.419437] [<ffffffff811bacdf>] ? do_vfs_ioctl+0x2cf/0x4b0 Apr 3 22:04:45 hpcore2 kernel: [ 3754.419463] [<ffffffff811baf41>] ? SyS_ioctl+0x81/0xa0 Apr 3 22:04:45 hpcore2 kernel: [ 3754.419487] [<ffffffff81516a28>] ? page_fault+0x28/0x30 Apr 3 22:04:45 hpcore2 kernel: [ 3754.419513] [<ffffffff81514a0d>] ? system_call_fast_compare_end+0x10/0x15 Apr 3 22:04:45 hpcore2 kernel: [ 3754.419543] Code: e4 48 8b 3b 89 c1 89 ea 48 c7 c6 80 b6 4f a0 31 c0 e8 68 57 f9 e0 eb cb 66 0f 1f 44 00 00 66 66 66 66 90 48 89 f8 ba 01 00 00 00 <f0> 0f c1 57 08 83 c2 01 83 fa 01 7e 01 c3 80 3d 0e 43 11 00 00 Apr 3 22:04:45 hpcore2 kernel: [ 3754.419839] RIP [<ffffffffa040bc3d>] radeon_fence_ref+0xd/0x50 [radeon] Apr 3 22:04:45 hpcore2 kernel: [ 3754.419883] RSP <ffff88007a9efb18> Apr 3 22:04:45 hpcore2 kernel: [ 3754.419898] CR2: 0000000000000008 Apr 3 22:04:45 hpcore2 kernel: [ 3754.430323] ---[ end trace 6f078410004efac7 ]--- Regards Patrice