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    Subject[PATCH 4.4 187/342] drm/amdgpu: hold reference to fences in amdgpu_sa_bo_new (v2)
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Nicolai Hähnle <nicolai.haehnle@amd.com>

    commit a8d81b36267366603771431747438d18f32ae2d5 upstream.

    An arbitrary amount of time can pass between spin_unlock and
    fence_wait_any_timeout, so we need to ensure that nobody frees the
    fences from under us.

    A stress test (rapidly starting and killing hundreds of glxgears
    instances) ran into a deadlock in fence_wait_any_timeout after
    about an hour, and this race condition appears to be a plausible
    cause.

    v2: agd: rebase on upstream

    Signed-off-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
    Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
    Reviewed-by: Christian König <christian.koenig@amd.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/gpu/drm/amd/amdgpu/amdgpu_sa.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_sa.c
    +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_sa.c
    @@ -354,12 +354,15 @@ int amdgpu_sa_bo_new(struct amdgpu_sa_ma

    for (i = 0, count = 0; i < AMDGPU_MAX_RINGS; ++i)
    if (fences[i])
    - fences[count++] = fences[i];
    + fences[count++] = fence_get(fences[i]);

    if (count) {
    spin_unlock(&sa_manager->wq.lock);
    t = fence_wait_any_timeout(fences, count, false,
    MAX_SCHEDULE_TIMEOUT);
    + for (i = 0; i < count; ++i)
    + fence_put(fences[i]);
    +
    r = (t > 0) ? 0 : t;
    spin_lock(&sa_manager->wq.lock);
    } else {
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