[ 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: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Gustavo Padovan <gustavo@xxxxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
---
drivers/dma-buf/dma-fence.c | 17 ++++++-----------
drivers/dma-buf/sync_debug.c | 2 +-
drivers/dma-buf/sync_file.c | 8 +++++++-
include/linux/dma-fence.h | 2 ++
4 files changed, 16 insertions(+), 13 deletions(-)
diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index d1f1f456f5c4..dd2d7b6d2831 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -74,11 +74,6 @@ 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;
@@ -86,8 +81,11 @@ 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);
@@ -114,14 +112,11 @@ 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)) {
diff --git a/drivers/dma-buf/sync_debug.c b/drivers/dma-buf/sync_debug.c
index c769dc653b34..bfead12390f2 100644
--- a/drivers/dma-buf/sync_debug.c
+++ b/drivers/dma-buf/sync_debug.c
@@ -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);
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 2321035f6204..95f259b719fc 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -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,
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 6048fa404e57..c3969e8b112a 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -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 */
};
--
2.11.0
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