• Chris Wilson's avatar
    dma-buf/fence: Avoid use of uninitialised timestamp · 76250f2b
    Chris Wilson authored
    
    
    [  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
    76250f2b
dma-fence.h 16.9 KB