[Intel-gfx] [PATCH] dma-resv: Fix dma_resv_get_fences and dma_resv_copy_fences after conversion
Christian König
christian.koenig at amd.com
Fri Oct 8 12:19:57 UTC 2021
Am 08.10.21 um 12:49 schrieb Tvrtko Ursulin:
>
> On 08/10/2021 11:21, Christian König wrote:
>> Am 08.10.21 um 11:50 schrieb Tvrtko Ursulin:
>>> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>>
>>> Cache the count of shared fences in the iterator to avoid dereferencing
>>> the dma_resv_object outside the RCU protection. Otherwise iterator
>>> and its
>>> users can observe an incosistent state which makes it impossible to use
>>> safely.
>>
>> Ah, of course! I've been staring at the code the whole morning and
>> couldn't see it.
>>
>> Going to write a testcase to cover that.
>>
>>> Such as:
>>>
>>> <6> [187.517041] [IGT] gem_sync: executing
>>> <7> [187.536343] i915 0000:00:02.0:
>>> [drm:i915_gem_context_create_ioctl [i915]] HW context 1 created
>>> <7> [187.536793] i915 0000:00:02.0:
>>> [drm:i915_gem_context_create_ioctl [i915]] HW context 1 created
>>> <6> [187.551235] [IGT] gem_sync: starting subtest basic-many-each
>>> <1> [188.935462] BUG: kernel NULL pointer dereference, address:
>>> 0000000000000010
>>> <1> [188.935485] #PF: supervisor write access in kernel mode
>>> <1> [188.935495] #PF: error_code(0x0002) - not-present page
>>> <6> [188.935504] PGD 0 P4D 0
>>> <4> [188.935512] Oops: 0002 [#1] PREEMPT SMP NOPTI
>>> <4> [188.935521] CPU: 2 PID: 1467 Comm: gem_sync Not tainted
>>> 5.15.0-rc4-CI-Patchwork_21264+ #1
>>> <4> [188.935535] Hardware name: /NUC6CAYB, BIOS
>>> AYAPLCEL.86A.0049.2018.0508.1356 05/08/2018
>>> <4> [188.935546] RIP: 0010:dma_resv_get_fences+0x116/0x2d0
>>> <4> [188.935560] Code: 10 85 c0 7f c9 be 03 00 00 00 e8 15 8b df ff
>>> eb bd e8 8e c6 ff ff eb b6 41 8b 04 24 49 8b 55 00 48 89 e7 8d 48 01
>>> 41 89 0c 24 <4c> 89 34 c2 e8 41 f2 ff ff 49 89 c6 48 85 c0 75 8c 48
>>> 8b 44 24 10
>>> <4> [188.935583] RSP: 0018:ffffc900011dbcc8 EFLAGS: 00010202
>>> <4> [188.935593] RAX: 0000000000000000 RBX: 00000000ffffffff RCX:
>>> 0000000000000001
>>> <4> [188.935603] RDX: 0000000000000010 RSI: ffffffff822e343c RDI:
>>> ffffc900011dbcc8
>>> <4> [188.935613] RBP: ffffc900011dbd48 R08: ffff88812d255bb8 R09:
>>> 00000000fffffffe
>>> <4> [188.935623] R10: 0000000000000001 R11: 0000000000000000 R12:
>>> ffffc900011dbd44
>>> <4> [188.935633] R13: ffffc900011dbd50 R14: ffff888113d29cc0 R15:
>>> 0000000000000000
>>> <4> [188.935643] FS: 00007f68d17e9700(0000)
>>> GS:ffff888277900000(0000) knlGS:0000000000000000
>>> <4> [188.935655] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> <4> [188.935665] CR2: 0000000000000010 CR3: 000000012d0a4000 CR4:
>>> 00000000003506e0
>>> <4> [188.935676] Call Trace:
>>> <4> [188.935685] i915_gem_object_wait+0x1ff/0x410 [i915]
>>> <4> [188.935988] i915_gem_wait_ioctl+0xf2/0x2a0 [i915]
>>> <4> [188.936272] ? i915_gem_object_wait+0x410/0x410 [i915]
>>> <4> [188.936533] drm_ioctl_kernel+0xae/0x140
>>> <4> [188.936546] drm_ioctl+0x201/0x3d0
>>> <4> [188.936555] ? i915_gem_object_wait+0x410/0x410 [i915]
>>> <4> [188.936820] ? __fget_files+0xc2/0x1c0
>>> <4> [188.936830] ? __fget_files+0xda/0x1c0
>>> <4> [188.936839] __x64_sys_ioctl+0x6d/0xa0
>>> <4> [188.936848] do_syscall_64+0x3a/0xb0
>>> <4> [188.936859] entry_SYSCALL_64_after_hwframe+0x44/0xae
>>>
>>> If the shared object has changed during the RCU unlocked period
>>> callers will correctly handle the restart on the next iteration.
>>>
>>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>> Fixes: 96601e8a4755 ("dma-buf: use new iterator in
>>> dma_resv_copy_fences")
>>> Fixes: d3c80698c9f5 ("dma-buf: use new iterator in
>>> dma_resv_get_fences v3")
>>> Closes:
>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fdrm%2Fintel%2F-%2Fissues%2F4274&data=04%7C01%7Cchristian.koenig%40amd.com%7Cc22feea06a3f4285cdac08d98a495984%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637692870805160909%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=6oPR30sWnJe04I4GlhhvJWX3QvwKFIOMW1uOIyWZFOE%3D&reserved=0
>>>
>>> Cc: Christian König <christian.koenig at amd.com>
>>> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>>> Cc: Sumit Semwal <sumit.semwal at linaro.org>
>>> Cc: linux-media at vger.kernel.org
>>> Cc: dri-devel at lists.freedesktop.org
>>> Cc: linaro-mm-sig at lists.linaro.org
>>
>> Maybe we should remove cursor->fences altogether, but either way the
>> patch is Reviewed-by: Christian König <christian.koenig at amd.com>
>>
>> Please push to drm-misc-next ASAP.
>
> Not sure I can or if my push permissions are limited to Intel
> branches. I can try once CI gives a green light.
If it doesn't work just ping me and I will push it.
Thanks,
Christian.
>
> Regards,
>
> Tvrtko
>
>>
>> Thanks,
>> Christian.
>>
>>> ---
>>> drivers/dma-buf/dma-resv.c | 18 ++++++++++--------
>>> include/linux/dma-resv.h | 5 ++++-
>>> 2 files changed, 14 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
>>> index a480af9581bd..7b6d881c8904 100644
>>> --- a/drivers/dma-buf/dma-resv.c
>>> +++ b/drivers/dma-buf/dma-resv.c
>>> @@ -333,10 +333,14 @@ static void
>>> dma_resv_iter_restart_unlocked(struct dma_resv_iter *cursor)
>>> {
>>> cursor->seq = read_seqcount_begin(&cursor->obj->seq);
>>> cursor->index = -1;
>>> - if (cursor->all_fences)
>>> + cursor->shared_count = 0;
>>> + if (cursor->all_fences) {
>>> cursor->fences = dma_resv_shared_list(cursor->obj);
>>> - else
>>> + if (cursor->fences)
>>> + cursor->shared_count = cursor->fences->shared_count;
>>> + } else {
>>> cursor->fences = NULL;
>>> + }
>>> cursor->is_restarted = true;
>>> }
>>> @@ -363,7 +367,7 @@ static void dma_resv_iter_walk_unlocked(struct
>>> dma_resv_iter *cursor)
>>> continue;
>>> } else if (!cursor->fences ||
>>> - cursor->index >= cursor->fences->shared_count) {
>>> + cursor->index >= cursor->shared_count) {
>>> cursor->fence = NULL;
>>> break;
>>> @@ -448,10 +452,8 @@ int dma_resv_copy_fences(struct dma_resv *dst,
>>> struct dma_resv *src)
>>> dma_resv_list_free(list);
>>> dma_fence_put(excl);
>>> - if (cursor.fences) {
>>> - unsigned int cnt = cursor.fences->shared_count;
>>> -
>>> - list = dma_resv_list_alloc(cnt);
>>> + if (cursor.shared_count) {
>>> + list = dma_resv_list_alloc(cursor.shared_count);
>>> if (!list) {
>>> dma_resv_iter_end(&cursor);
>>> return -ENOMEM;
>>> @@ -522,7 +524,7 @@ int dma_resv_get_fences(struct dma_resv *obj,
>>> struct dma_fence **fence_excl,
>>> if (fence_excl)
>>> dma_fence_put(*fence_excl);
>>> - count = cursor.fences ? cursor.fences->shared_count : 0;
>>> + count = cursor.shared_count;
>>> count += fence_excl ? 0 : 1;
>>> /* Eventually re-allocate the array */
>>> diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
>>> index 8b6c20636a79..3e1bff147428 100644
>>> --- a/include/linux/dma-resv.h
>>> +++ b/include/linux/dma-resv.h
>>> @@ -170,9 +170,12 @@ struct dma_resv_iter {
>>> /** @index: index into the shared fences */
>>> unsigned int index;
>>> - /** @fences: the shared fences */
>>> + /** @fences: the shared fences; private, *MUST* not
>>> dereference */
>>> struct dma_resv_list *fences;
>>> + /** @shared_count: number of shared fences */
>>> + unsigned int shared_count;
>>> +
>>> /** @is_restarted: true if this is the first returned fence */
>>> bool is_restarted;
>>> };
>>
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