Commit 76250f2b authored by Chris Wilson's avatar Chris Wilson Committed by Gustavo Padovan
Browse files

dma-buf/fence: Avoid use of uninitialised timestamp



[  236.821534] WARNING: kmemcheck: Caught 64-bit read from uninitialized memory (ffff8802538683d0)
[  236.828642] 420000001e7f0000000000000000000000080000000000000000000000000000
[  236.839543]  i i i i u u u u i i i i i i i i u u u u u u u u u u u u u u u u
[  236.850420]                                  ^
[  236.854123] RIP: 0010:[<ffffffff81396f07>]  [<ffffffff81396f07>] fence_signal+0x17/0xd0
[  236.861313] RSP: 0018:ffff88024acd7ba0  EFLAGS: 00010282
[  236.865027] RAX: ffffffff812f6a90 RBX: ffff8802527ca800 RCX: ffff880252cb30e0
[  236.868801] RDX: ffff88024ac5d918 RSI: ffff880252f780e0 RDI: ffff880253868380
[  236.872579] RBP: ffff88024acd7bc0 R08: ffff88024acd7be0 R09: 0000000000000000
[  236.876407] R10: 0000000000000000 R11: 0000000000000000 R12: ffff880253868380
[  236.880185] R13: ffff8802538684d0 R14: ffff880253868380 R15: ffff88024cd48e00
[  236.883983] FS:  00007f1646d1a740(0000) GS:ffff88025d000000(0000) knlGS:0000000000000000
[  236.890959] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  236.894702] CR2: ffff880251360318 CR3: 000000024ad21000 CR4: 00000000001406f0
[  236.898481]  [<ffffffff8130d1ad>] i915_gem_request_retire+0x1cd/0x230
[  236.902439]  [<ffffffff8130e2b3>] i915_gem_request_alloc+0xa3/0x2f0
[  236.906435]  [<ffffffff812fb1bd>] i915_gem_do_execbuffer.isra.41+0xb6d/0x18b0
[  236.910434]  [<ffffffff812fc265>] i915_gem_execbuffer2+0x95/0x1e0
[  236.914390]  [<ffffffff812ad625>] drm_ioctl+0x1e5/0x460
[  236.918275]  [<ffffffff8110d4cf>] do_vfs_ioctl+0x8f/0x5c0
[  236.922168]  [<ffffffff8110da3c>] SyS_ioctl+0x3c/0x70
[  236.926090]  [<ffffffff814b7a5f>] entry_SYSCALL_64_fastpath+0x17/0x93
[  236.930045]  [<ffffffffffffffff>] 0xffffffffffffffff

We only set the timestamp before we mark the fence as signaled. It is
done before to avoid observers having a window in which they may see the
fence as complete but no timestamp. Having it does incur a potential for
the timestamp to be written twice, and even for it to be corrupted if
the u64 write is not atomic. Instead use a new bit to record the
presence of the timestamp, and teach the readers to wait until it is set
if the fence is complete. There still remains a race where the timestamp
for the signaled fence may be shown before the fence is reported as
signaled, but that's a pre-existing error.
Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Reported-by: default avatarRafael Antognolli <rafael.antognolli@intel.com>
Signed-off-by: default avatarGustavo Padovan <gustavo.padovan@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170214124001.1930-1-chris@chris-wilson.co.uk
parent e94ac351
......@@ -75,11 +75,6 @@ int dma_fence_signal_locked(struct dma_fence *fence)
if (WARN_ON(!fence))
return -EINVAL;
if (!ktime_to_ns(fence->timestamp)) {
fence->timestamp = ktime_get();
smp_mb__before_atomic();
}
if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
ret = -EINVAL;
......@@ -87,8 +82,11 @@ int dma_fence_signal_locked(struct dma_fence *fence)
* we might have raced with the unlocked dma_fence_signal,
* still run through all callbacks
*/
} else
} else {
fence->timestamp = ktime_get();
set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
trace_dma_fence_signaled(fence);
}
list_for_each_entry_safe(cur, tmp, &fence->cb_list, node) {
list_del_init(&cur->node);
......@@ -115,14 +113,11 @@ int dma_fence_signal(struct dma_fence *fence)
if (!fence)
return -EINVAL;
if (!ktime_to_ns(fence->timestamp)) {
fence->timestamp = ktime_get();
smp_mb__before_atomic();
}
if (test_and_set_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
return -EINVAL;
fence->timestamp = ktime_get();
set_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags);
trace_dma_fence_signaled(fence);
if (test_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &fence->flags)) {
......
......@@ -84,7 +84,7 @@ static void sync_print_fence(struct seq_file *s,
show ? "_" : "",
sync_status_str(status));
if (status) {
if (test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags)) {
struct timespec64 ts64 =
ktime_to_timespec64(fence->timestamp);
......
......@@ -375,7 +375,13 @@ static void sync_fill_fence_info(struct dma_fence *fence,
sizeof(info->driver_name));
info->status = dma_fence_get_status(fence);
info->timestamp_ns = ktime_to_ns(fence->timestamp);
while (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) &&
!test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags))
cpu_relax();
info->timestamp_ns =
test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags) ?
ktime_to_ns(fence->timestamp) :
ktime_set(0, 0);
}
static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
......
......@@ -55,6 +55,7 @@ struct dma_fence_cb;
* of the time.
*
* DMA_FENCE_FLAG_SIGNALED_BIT - fence is already signaled
* DMA_FENCE_FLAG_TIMESTAMP_BIT - timestamp recorded for fence signaling
* DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT - enable_signaling might have been called
* DMA_FENCE_FLAG_USER_BITS - start of the unused bits, can be used by the
* implementer of the fence for its own purposes. Can be used in different
......@@ -84,6 +85,7 @@ struct dma_fence {
enum dma_fence_flag_bits {
DMA_FENCE_FLAG_SIGNALED_BIT,
DMA_FENCE_FLAG_TIMESTAMP_BIT,
DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT,
DMA_FENCE_FLAG_USER_BITS, /* must always be last member */
};
......
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