<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=us-ascii"> <style style="display: none;" id="owaParaStyle" type="text/css">P {margin-top:0;margin-bottom:0;}</style><style id="owaParaStyle" type="text/css" style="">  </style><style id="owaParaStyle" type="text/css" style="">  </style> </head> <body id="" tabindex="0" aria-label="Message body" fpstyle="1" dir="ltr"> <div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="font-family: Calibri,Arial,Helvetica,sans-serif; font-size: 12pt; color: #000000; margin: 0"> <div style="color: rgb(40, 40, 40);" dir="ltr"> <div> <div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:#000000; margin:0"> <div dir="ltr" style="color:rgb(40,40,40)"> <div> <div name="divtagdefaultwrapper" id="divtagdefaultwrapper" style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:#000000; margin:0"> Hello guys, I've been playing with reloading intel gfx driver (i915) in a cycle, for a while, and at some point I've found a non-deterministic kernel crash with a highly-variable iteration dependency -- 2 to 200 driver reload iterations. The apparent race is over the shared internal string buffer in drm_get_connector_name(). It is mostly harmless, due to its results being mostly used for log output, but in at least one case -- drm_sysfs_connector_add() -- this leads to a more critical error. Race scenario: - drm_sysfs_connector_add() - drm_get_connector_name() vs. - anything that generates log messages involving DRM connectors - drm_get_connector_name() (and many other from drm_crtc.c) shares with caller const char* to internal static char buffer. If something call it from other thread, while main thread strore and use returned pointer it may overwrite connector name. Here are we go: registering HDMI connecter (drm_sysfs_connector_add store and use pointer from drm_get_connector_name) and the same time got VGA connector name down through the stack. (the second thread is upowerd who watch continuously sysfs) Mar 24 14:23:04 haswell01 kernel: [ 417.570043] ------------[ cut here ]------------ Mar 24 14:23:04 haswell01 kernel: [ 417.570045] WARNING: CPU: 0 PID: 12700 at /build/buildd/linux-3.13.0/lib/kobject.c:223 kobject_add_internal+0x224/0x330() Mar 24 14:23:04 haswell01 kernel: [ 417.570046] kobject_add_internal failed for card0-VGA-1 with -EEXIST, don't try to register things with the same name in the same directory. Mar 24 14:23:04 haswell01 kernel: [ 417.570047] Modules linked in: i915(+) video drm_kms_helper drm i2c_algo_bit snd_hda_codec_realtek snd_hda_codec_hdmi bnep rfcomm bluetooth x86_pkg_temp_thermal intel_p owerclamp coretemp kvm_intel snd_hda_codec kvm snd_hwdep snd_pcm hid_generic snd_page_alloc crct10dif_pclmul snd_seq_midi crc32_pclmul ghash_clmulni_intel snd_seq_midi_event usbhid snd_rawmidi hid aesni_in tel aes_x86_64 lrw gf128mul ppdev glue_helper ablk_helper cryptd snd_seq snd_seq_device snd_timer snd mei_me psmouse lpc_ich soundcore mei mac_hid parport_pc serio_raw nls_iso8859_1 lp parport e1000e ahci ptp libahci pps_core [last unloaded: video] Mar 24 14:23:04 haswell01 kernel: [ 417.570068] CPU: 0 PID: 12700 Comm: modprobe Tainted: G W 3.13.0-19-generic #39-Ubuntu Mar 24 14:23:04 haswell01 kernel: [ 417.570069] Hardware name: /DQ87PG, BIOS PGQ8710H.86A.0144.2014.0113.1604 01/13/2014 Mar 24 14:23:04 haswell01 kernel: [ 417.570069] 0000000000000009 ffff8804051295f8 ffffffff81711075 ffff880405129640 Mar 24 14:23:04 haswell01 kernel: [ 417.570071] ffff880405129630 ffffffff810662cd ffff88040776a410 00000000ffffffef Mar 24 14:23:04 haswell01 kernel: [ 417.570074] 0000000000000000 ffff8804048dcc10 ffff880407769000 ffff880405129690 Mar 24 14:23:04 haswell01 kernel: [ 417.570076] Call Trace: Mar 24 14:23:04 haswell01 kernel: [ 417.570078] [<ffffffff81711075>] dump_stack+0x45/0x56 Mar 24 14:23:04 haswell01 kernel: [ 417.570080] [<ffffffff810662cd>] warn_slowpath_common+0x7d/0xa0 Mar 24 14:23:04 haswell01 kernel: [ 417.570081] [<ffffffff8106633c>] warn_slowpath_fmt+0x4c/0x50 Mar 24 14:23:04 haswell01 kernel: [ 417.570082] [<ffffffff81230083>] ? sysfs_create_dir_ns+0x73/0xc0 Mar 24 14:23:04 haswell01 kernel: [ 417.570084] [<ffffffff8135b9a4>] kobject_add_internal+0x224/0x330 Mar 24 14:23:04 haswell01 kernel: [ 417.570086] [<ffffffff8135bed5>] kobject_add+0x65/0xb0 Mar 24 14:23:04 haswell01 kernel: [ 417.570088] [<ffffffff814874f5>] device_add+0x125/0x640 Mar 24 14:23:04 haswell01 kernel: [ 417.570090] [<ffffffff81487c20>] device_create_groups_vargs+0xe0/0x110 Mar 24 14:23:04 haswell01 kernel: [ 417.570092] [<ffffffff81487cb1>] device_create+0x41/0x50 Mar 24 14:23:04 haswell01 kernel: [ 417.570097] [<ffffffffa0137fc9>] drm_sysfs_connector_add+0x69/0x230 [drm] Mar 24 14:23:04 haswell01 kernel: [ 417.570110] [<ffffffffa0549ca1>] intel_hdmi_init_connector+0x111/0x260 [i915] Mar 24 14:23:04 haswell01 kernel: [ 417.570119] [<ffffffffa0541670>] intel_ddi_init+0x270/0x2a0 [i915] Mar 24 14:23:04 haswell01 kernel: [ 417.570130] [<ffffffffa0533176>] intel_setup_outputs+0x4c6/0x750 [i915] Mar 24 14:23:04 haswell01 kernel: [ 417.570139] [<ffffffffa05370f7>] intel_modeset_init+0x607/0x8f0 [i915] Mar 24 14:23:04 haswell01 kernel: [ 417.570147] [<ffffffffa04f90a4>] i915_driver_load+0xbb4/0xe70 [i915] Mar 24 14:23:04 haswell01 kernel: [ 417.570153] [<ffffffffa0134cd2>] drm_dev_register+0xa2/0x1e0 [drm] Mar 24 14:23:04 haswell01 kernel: [ 417.570158] [<ffffffffa0136bc2>] drm_get_pci_dev+0x92/0x140 [drm] Mar 24 14:23:04 haswell01 kernel: [ 417.570166] [<ffffffffa04f567c>] i915_pci_probe+0x3c/0x90 [i915] Mar 24 14:23:04 haswell01 kernel: [ 417.570168] [<ffffffff8139e0e5>] local_pci_probe+0x45/0xa0 Mar 24 14:23:04 haswell01 kernel: [ 417.570170] [<ffffffff8139f385>] ? pci_match_device+0xc5/0xd0 Mar 24 14:23:04 haswell01 kernel: [ 417.570172] [<ffffffff8139f4a9>] pci_device_probe+0xd9/0x130 Mar 24 14:23:04 haswell01 kernel: [ 417.570174] [<ffffffff8148a7c5>] driver_probe_device+0x125/0x3b0 Mar 24 14:23:04 haswell01 kernel: [ 417.570176] [<ffffffff8148ab23>] __driver_attach+0x93/0xa0 Mar 24 14:23:04 haswell01 kernel: [ 417.570178] [<ffffffff8148aa90>] ? __device_attach+0x40/0x40 Mar 24 14:23:04 haswell01 kernel: [ 417.570179] [<ffffffff81488733>] bus_for_each_dev+0x63/0xa0 Mar 24 14:23:04 haswell01 kernel: [ 417.570181] [<ffffffff8148a17e>] driver_attach+0x1e/0x20 Mar 24 14:23:04 haswell01 kernel: [ 417.570183] [<ffffffff81489d60>] bus_add_driver+0x180/0x250 Mar 24 14:23:04 haswell01 kernel: [ 417.570185] [<ffffffffa01be000>] ? 0xffffffffa01bdfff Mar 24 14:23:04 haswell01 kernel: [ 417.570187] [<ffffffff8148b1a4>] driver_register+0x64/0xf0 Mar 24 14:23:04 haswell01 kernel: [ 417.570189] [<ffffffffa01be000>] ? 0xffffffffa01bdfff Mar 24 14:23:04 haswell01 kernel: [ 417.570191] [<ffffffff8139da7c>] __pci_register_driver+0x4c/0x50 Mar 24 14:23:04 haswell01 kernel: [ 417.570196] [<ffffffffa0136d8a>] drm_pci_init+0x11a/0x130 [drm] Mar 24 14:23:04 haswell01 kernel: [ 417.570198] [<ffffffffa01be000>] ? 0xffffffffa01bdfff Mar 24 14:23:04 haswell01 kernel: [ 417.570205] [<ffffffffa01be066>] i915_init+0x66/0x68 [i915] Mar 24 14:23:04 haswell01 kernel: [ 417.570207] [<ffffffff8100214a>] do_one_initcall+0xfa/0x1b0 Mar 24 14:23:04 haswell01 kernel: [ 417.570208] [<ffffffff81058ae3>] ? set_memory_nx+0x43/0x50 Mar 24 14:23:04 haswell01 kernel: [ 417.570211] [<ffffffff810e091d>] load_module+0x12dd/0x1b40 Mar 24 14:23:04 haswell01 kernel: [ 417.570213] [<ffffffff810dc3a0>] ? store_uevent+0x40/0x40 Mar 24 14:23:04 haswell01 kernel: [ 417.570215] [<ffffffff810e12f6>] SyS_finit_module+0x86/0xb0 Mar 24 14:23:04 haswell01 kernel: [ 417.570217] [<ffffffff81721c7f>] tracesys+0xe1/0xe6 Mar 24 14:23:04 haswell01 kernel: [ 417.570219] ---[ end trace 8cd466c13137554f ]--- How to reproduce: load/reload i915 driver many times (in my case it happens after 2-200 attempts) and you will got a sysfs dup warning and then while unloading driver it will crash (because of malformed connectors list): Mar 24 14:23:16 haswell01 kernel: [ 429.326174] BUG: unable to handle kernel NULL pointer dereference at 000000000000002f Mar 24 14:23:16 haswell01 kernel: [ 429.326177] IP: [<ffffffff8122de46>] sysfs_remove_file_ns+0x6/0x20 Mar 24 14:23:16 haswell01 kernel: [ 429.326184] PGD 3f588d067 PUD 406361067 PMD 0 Mar 24 14:23:16 haswell01 kernel: [ 429.326187] Oops: 0000 [#1] SMP Mar 24 14:23:16 haswell01 kernel: [ 429.326189] Modules linked in: i915 video drm_kms_helper drm i2c_algo_bit snd_hda_codec_realtek snd_hda_codec_hdmi bnep rfcomm bluetooth x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel snd_hda_codec kvm snd_hwdep snd_pcm hid_generic snd_page_alloc crct10dif_pclmul snd_seq_midi crc32_pclmul ghash_clmulni_intel snd_seq_midi_event usbhid snd_rawmidi hid aesni_intel aes_x86_64 lrw gf128mul ppdev glue_helper ablk_helper cryptd snd_seq snd_seq_device snd_timer snd mei_me psmouse lpc_ich soundcore mei mac_hid parport_pc serio_raw nls_iso8859_1 lp parport e1000e ahci ptp libahci pps_core [last unloaded: video] Mar 24 14:23:16 haswell01 kernel: [ 429.326219] CPU: 0 PID: 13302 Comm: dd Tainted: G W 3.13.0-19-generic #39-Ubuntu Mar 24 14:23:16 haswell01 kernel: [ 429.326221] Hardware name: /DQ87PG, BIOS PGQ8710H.86A.0144.2014.0113.1604 01/13/2014 Mar 24 14:23:16 haswell01 kernel: [ 429.326222] task: ffff8803f5aaafe0 ti: ffff880404d20000 task.ti: ffff880404d20000 Mar 24 14:23:16 haswell01 kernel: [ 429.326224] RIP: 0010:[<ffffffff8122de46>] [<ffffffff8122de46>] sysfs_remove_file_ns+0x6/0x20 Mar 24 14:23:16 haswell01 kernel: [ 429.326227] RSP: 0018:ffff880404d21d20 EFLAGS: 00010246 Mar 24 14:23:16 haswell01 kernel: [ 429.326228] RAX: 0000000000000000 RBX: ffffffffa0160160 RCX: ffffffffa0159356 Mar 24 14:23:16 haswell01 kernel: [ 429.326230] RDX: 0000000000000000 RSI: ffffffffa0160140 RDI: ffffffffffffffff Mar 24 14:23:16 haswell01 kernel: [ 429.326231] RBP: ffff880404d21d30 R08: ffffffffa0161120 R09: 000000000000fffe Mar 24 14:23:16 haswell01 kernel: [ 429.326232] R10: 0000000000000000 R11: ffffea0010199f80 R12: ffff880407769000 Mar 24 14:23:16 haswell01 kernel: [ 429.326234] R13: ffff880035d46af8 R14: ffff880035d46820 R15: ffffffffffffffed Mar 24 14:23:16 haswell01 kernel: [ 429.326236] FS: 00007f472f4ec740(0000) GS:ffff88041ea00000(0000) knlGS:0000000000000000 Mar 24 14:23:16 haswell01 kernel: [ 429.326238] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 Mar 24 14:23:16 haswell01 kernel: [ 429.326239] CR2: 000000000000002f CR3: 00000004050d3000 CR4: 00000000001407f0 Mar 24 14:23:16 haswell01 kernel: [ 429.326241] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 Mar 24 14:23:16 haswell01 kernel: [ 429.326242] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Mar 24 14:23:16 haswell01 kernel: [ 429.326243] Stack: Mar 24 14:23:16 haswell01 kernel: [ 429.326244] ffff880404d21d30 ffffffff81485a59 ffff880404d21d50 ffffffffa0137eb7 Mar 24 14:23:16 haswell01 kernel: [ 429.326247] ffff880407769000 ffff880035d46800 ffff880404d21d80 ffffffffa05381d0 Mar 24 14:23:16 haswell01 kernel: [ 429.326250] ffff8803f24e4000 ffff880035d46800 ffff8804081b9000 000000000000000c Mar 24 14:23:16 haswell01 kernel: [ 429.326253] Call Trace: Mar 24 14:23:16 haswell01 kernel: [ 429.326257] [<ffffffff81485a59>] ? device_remove_file+0x19/0x20 Mar 24 14:23:16 haswell01 kernel: [ 429.326267] [<ffffffffa0137eb7>] drm_sysfs_connector_remove+0x57/0x90 [drm] Mar 24 14:23:16 haswell01 kernel: [ 429.326282] [<ffffffffa05381d0>] intel_modeset_cleanup+0xd0/0x100 [i915] Mar 24 14:23:16 haswell01 kernel: [ 429.326288] [<ffffffffa04f95f0>] i915_driver_unload+0x290/0x340 [i915] Mar 24 14:23:16 haswell01 kernel: [ 429.326294] [<ffffffffa01346fc>] drm_dev_unregister+0x2c/0xe0 [drm] Mar 24 14:23:16 haswell01 kernel: [ 429.326299] [<ffffffffa01347eb>] drm_put_dev+0x3b/0x70 [drm] Mar 24 14:23:16 haswell01 kernel: [ 429.326304] [<ffffffffa04f558d>] i915_pci_remove+0x1d/0x20 [i915] Mar 24 14:23:16 haswell01 kernel: [ 429.326307] [<ffffffff8139efbb>] pci_device_remove+0x3b/0xb0 Mar 24 14:23:16 haswell01 kernel: [ 429.326310] [<ffffffff8148a24f>] __device_release_driver+0x7f/0xf0 Mar 24 14:23:16 haswell01 kernel: [ 429.326313] [<ffffffff8148a2e3>] device_release_driver+0x23/0x30 Mar 24 14:23:16 haswell01 kernel: [ 429.326315] [<ffffffff8148905d>] unbind_store+0xbd/0xe0 Mar 24 14:23:16 haswell01 kernel: [ 429.326317] [<ffffffff81488484>] drv_attr_store+0x24/0x40 Mar 24 14:23:16 haswell01 kernel: [ 429.326320] [<ffffffff8122e698>] sysfs_write_file+0x128/0x1c0 Mar 24 14:23:16 haswell01 kernel: [ 429.326323] [<ffffffff811b88c4>] vfs_write+0xb4/0x1f0 Mar 24 14:23:16 haswell01 kernel: [ 429.326325] [<ffffffff811b92f9>] SyS_write+0x49/0xa0 Mar 24 14:23:16 haswell01 kernel: [ 429.326328] [<ffffffff81721c7f>] tracesys+0xe1/0xe6 Mar 24 14:23:16 haswell01 kernel: [ 429.326329] Code: 58 c7 81 e8 7d 98 4e 00 48 83 c4 50 89 d8 5b 41 5c 41 5d 5d c3 bb fe ff ff ff eb e0 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 55 <48> 8b 7f 30 48 8b 36 48 89 e5 e8 bb 22 00 00 5d c3 66 0f 1f 84 Mar 24 14:23:16 haswell01 kernel: [ 429.326351] RIP [<ffffffff8122de46>] sysfs_remove_file_ns+0x6/0x20 Mar 24 14:23:16 haswell01 kernel: [ 429.326353] RSP <ffff880404d21d20> Mar 24 14:23:16 haswell01 kernel: [ 429.326355] CR2: 000000000000002f Mar 24 14:23:16 haswell01 kernel: [ 429.326356] ---[ end trace 8cd466c131375550 ]--- </div> </div> </div> </div> </div> </div> </div> </body> </html>