Whilst running the shrinker, we need to hold a reference as we unbind the objects, or else we may end up waiting for and retiring requests, which in turn may result in this object being freed. This is very similar to the eviction code which also has to be very careful to keep a reference to its objects as it retires and unbinds them. Another similarity, that Ben pointed out, is that as we may call retire-requests, the unbound_list is outside of our control. We must only process a single element of that list at a time, that is we can not rely on the "safe" next pointer being valid after a call to i915_vma_unbind(). BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 IP: [<ffffffffa0082892>] i915_gem_gtt_finish_object+0x68/0xbd [i915] PGD 758d3067 PUD ac0d6067 PMD 0 Oops: 0000 [#1] SMP Modules linked in: dm_mod snd_hda_codec_realtek iTCO_wdt iTCO_vendor_support pcspkr snd_hda_intel i2c_i801 snd_hda_codec snd_hwdep snd_pcm snd_page_alloc snd_timer snd lpc_ich mfd_core soundcore battery ac option usb_wwan usbserial uvcvideo videobuf2_vmalloc videobuf2_memops videobuf2_core videodev i915 video button drm_kms_helper drm acpi_cpufreq mperf freq_table CPU: 1 PID: 16835 Comm: fbo-maxsize Not tainted 3.11.0-rc7_nightlytop_8fdad4_20130902_+ #7977 task: ffff8800712106d0 ti: ffff880028e4a000 task.ti: ffff880028e4a000 RIP: 0010:[<ffffffffa0082892>] [<ffffffffa0082892>] i915_gem_gtt_finish_object+0x68/0xbd [i915] RSP: 0018:ffff880028e4b9e8 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff880145734000 RCX: ffff880145735328 RDX: ffff8801457353fc RSI: 0000000000000000 RDI: ffff88007597cc00 RBP: ffff88007597cc00 R08: 0000000000000001 R09: ffff88014f257f00 R10: ffffea0001d65f00 R11: 0000000000bba60b R12: ffff880149e5b000 R13: ffff880145734001 R14: ffff88007597ccc8 R15: ffff88007597cc00 FS: 00007ff5bc919740(0000) GS:ffff88014f240000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000008 CR3: 0000000028f4c000 CR4: 00000000001407e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Stack: 0000000000000000 ffff88007597cc00 ffff8801440d6840 0000000000000000 ffff880145734000 ffffffffa007c854 0000000000000010 ffff88007597c900 0000000000018000 00000000004a1201 ffff88007597cc60 ffffffffa007d183 Call Trace: [<ffffffffa007c854>] ? i915_vma_unbind+0xe2/0x1d1 [i915] [<ffffffffa007d183>] ? __i915_gem_shrink+0xf1/0x162 [i915] [<ffffffffa007d2ee>] ? i915_gem_object_get_pages_gtt+0xfa/0x303 [i915] [<ffffffffa00795f4>] ? i915_gem_object_get_pages+0x54/0x89 [i915] [<ffffffffa007cbda>] ? i915_gem_object_pin+0x238/0x5ce [i915] [<ffffffff812cba5f>] ? __sg_page_iter_next+0x2b/0x58 [<ffffffffa0082056>] ? gen6_ppgtt_insert_entries+0xf2/0x114 [i915] [<ffffffffa007fe4b>] ? i915_gem_execbuffer_reserve_vma.isra.13+0x79/0x18d [i915] [<ffffffffa008017c>] ? i915_gem_execbuffer_reserve+0x21d/0x347 [i915] [<ffffffffa0080bfb>] ? i915_gem_do_execbuffer.isra.17+0x4f3/0xe61 [i915] [<ffffffffa00795f4>] ? i915_gem_object_get_pages+0x54/0x89 [i915] [<ffffffffa007e405>] ? i915_gem_pwrite_ioctl+0x743/0x7a5 [i915] [<ffffffffa0081a46>] ? i915_gem_execbuffer2+0x15e/0x1e4 [i915] [<ffffffffa000e20d>] ? drm_ioctl+0x2a5/0x3c4 [drm] [<ffffffffa00818e8>] ? i915_gem_execbuffer+0x37f/0x37f [i915] [<ffffffff816f64c0>] ? __do_page_fault+0x3ab/0x449 [<ffffffff810be3da>] ? do_mmap_pgoff+0x2b2/0x341 [<ffffffff810e49be>] ? vfs_ioctl+0x1e/0x31 [<ffffffff810e5194>] ? do_vfs_ioctl+0x3ad/0x3ef [<ffffffff810e5224>] ? SyS_ioctl+0x4e/0x7e [<ffffffff816f88d2>] ? system_call_fastpath+0x16/0x1b Code: 52 0c a0 48 c7 c6 22 30 0d a0 31 c0 e8 ef 00 f9 ff bf c6 a7 00 00 e8 90 5d 24 e1 f6 85 13 01 00 00 10 75 44 48 8b 85 18 01 00 00 <8b> 50 08 48 8b 30 49 8b 84 24 88 02 00 00 48 89 c7 48 81 c7 98 RIP [<ffffffffa0082892>] i915_gem_gtt_finish_object+0x68/0xbd [i915] RSP <ffff880028e4b9e8> CR2: 0000000000000008 Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=68171 Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx --- drivers/gpu/drm/i915/i915_gem.c | 31 +++++++++++++++++++++++++------ 1 file changed, 25 insertions(+), 6 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index fdeecae..c31e0b2 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -1695,6 +1695,7 @@ static long __i915_gem_shrink(struct drm_i915_private *dev_priv, long target, bool purgeable_only) { + struct list_head still_bound_list; struct drm_i915_gem_object *obj, *next; long count = 0; @@ -1709,23 +1710,41 @@ __i915_gem_shrink(struct drm_i915_private *dev_priv, long target, } } - list_for_each_entry_safe(obj, next, &dev_priv->mm.bound_list, - global_list) { + /* As we may completely rewrite the bound list whilst unbinding + * (due to retiring requests) we have to strictly process only + * one element of the list at the time, and recheck the list + * on every iteration. + */ + INIT_LIST_HEAD(&still_bound_list); + while (count < target && !list_empty(&dev_priv->mm.bound_list)) { struct i915_vma *vma, *v; + obj = list_first_entry(&dev_priv->mm.bound_list, + typeof(*obj), global_list); + list_move_tail(&obj->global_list, &still_bound_list); + if (!i915_gem_object_is_purgeable(obj) && purgeable_only) continue; + /* Hold a reference whilst we unbind this object, as we may + * end up waiting for and retiring requests, which may result + * in this object being freed. + * + * Note that the shrinker and eviction is special as they operate + * on the inactive lists which reference limbo objects. + */ + drm_gem_object_reference(&obj->base); + list_for_each_entry_safe(vma, v, &obj->vma_list, vma_link) if (i915_vma_unbind(vma)) break; - if (!i915_gem_object_put_pages(obj)) { + if (i915_gem_object_put_pages(obj) == 0) count += obj->base.size >> PAGE_SHIFT; - if (count >= target) - return count; - } + + drm_gem_object_unreference(&obj->base); } + list_splice(&still_bound_list, &dev_priv->mm.bound_list); return count; } -- 1.8.4.rc3 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html