drm/i915/gem: Avoid iterating an empty list
authorChris Wilson <chris@chris-wilson.co.uk>
Fri, 22 May 2020 13:27:06 +0000 (14:27 +0100)
committerJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Mon, 25 May 2020 12:40:43 +0000 (15:40 +0300)
commit757a9395f33c51c4e6eff2c7c0fbd50226a58224
tree1f79938cec04d75f6a8ed2f6379501a6bba792d8
parentef29440b3ccb93f44cf664311b30fbd5f84d9683
drm/i915/gem: Avoid iterating an empty list

Our __sgt_iter assumes that the scattergather list has at least one
element. But during construction we may fail in allocating the first
page, and so mark the first element as the terminator. This is
unexpected!

[22555.524752] RIP: 0010:shmem_get_pages+0x506/0x710 [i915]
[22555.524759] Code: 49 8b 2c 24 31 c0 66 89 44 24 40 48 85 ed 0f 84 62 01 00 00 4c 8b 75 00 8b 5d 08 44 8b 7d 0c 48 8b 0d 7e 34 07 e2 49 83 e6 fc <49> 8b 16 41 01 df 48 89 cf 48 89 d0 48 c1 e8 2d 48 85 c9 0f 84 c8
[22555.524765] RSP: 0018:ffffc9000053f9d0 EFLAGS: 00010246
[22555.524770] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff8881ffffa000
[22555.524774] RDX: fffffffffffffff4 RSI: ffffffffffffffff RDI: ffffffff821efe00
[22555.524778] RBP: ffff8881b099ab00 R08: 0000000000000000 R09: 00000000fffffff4
[22555.524782] R10: 0000000000000002 R11: 00000000ffec0a02 R12: ffff8881cd3c8d60
[22555.524786] R13: 00000000fffffff4 R14: 0000000000000000 R15: 0000000000000000
[22555.524790] FS:  00007f4fbeb9b9c0(0000) GS:ffff8881f8580000(0000) knlGS:0000000000000000
[22555.524795] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[22555.524799] CR2: 0000000000000000 CR3: 00000001ec7f0004 CR4: 00000000001606e0
[22555.524803] Call Trace:
[22555.524919]  __i915_gem_object_get_pages+0x4f/0x60 [i915]

Fixes: 85d1225ec066 ("drm/i915: Introduce & use new lightweight SGL iterators")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: <stable@vger.kernel.org> # v4.8+
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Maciej Patelczyk <maciej.patelczyk@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200522132706.5133-1-chris@chris-wilson.co.uk
(cherry picked from commit 957ad9a02be6faa87594c58ac09460cd3d190d0e)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
drivers/gpu/drm/i915/gem/i915_gem_shmem.c