[Intel-gfx] [PATCH] dma-buf/fence: Avoid use of uninitialised timestamp
Gustavo Padovan
gustavo at padovan.org
Fri Jul 14 19:20:19 UTC 2017
2017-07-11 Chris Wilson <chris at chris-wilson.co.uk>:
> Quoting Chris Wilson (2017-02-14 12:40:01)
> > [ 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
>
> Ah something that I didn't take into account, and indeed gives this a bit
> more urgency than I realised, is that the timestamp is exposed to
> userspace. As such we are feeding it garbage, at best.
>
> The trivial option is just to clear it in dma_fence_init(). I still have
> the slight preference for the extra complication here (for the reader) as
> it should be quicker for the more common path of signaling the fence.
>
> > 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.
>
> Now deserves a
> Reported-by: Rafael Antognolli <rafael.antognolli at intel.com>
>
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Sumit Semwal <sumit.semwal at linaro.org>
> > Cc: Gustavo Padovan <gustavo at padovan.org>
> > Cc: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Rafael Antognolli <rafael.antognolli at intel.com>
>
> > ---
> > 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(-)
Finally pushed this one to drm-misc-fixes. Thanks.
Gustavo
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