From: Chris Wilson Date: Tue, 9 Jul 2013 08:22:39 +0000 (+0100) Subject: drm/i915: Fix write-read race with multiple rings X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=02978ff57a5bdfbf703d2bc5a4d933a53ede3144;p=linux-beck.git drm/i915: Fix write-read race with multiple rings Daniel noticed a problem where is we wrote to an object with ring A in the middle of a very long running batch, then executed a quick batch on ring B before a batch that reads from the same object, its obj->ring would now point to ring B, but its last_write_seqno would be still relative to ring A. This would allow for the user to read from the object before the GPU had completed the write, as set_domain would only check that ring B had passed the last_write_seqno. To fix this simply (and inelegantly), we bump the last_write_seqno when switching rings so that the last_write_seqno is always relative to the current obj->ring. This fixes igt/tests/gem_write_read_ring_switch. Signed-off-by: Chris Wilson Cc: Daniel Vetter Cc: stable@vger.kernel.org [danvet: Add note about the newly created igt which exercises this bug.] Signed-off-by: Daniel Vetter --- diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 7f368d79f7d2..8fd8e82ebda4 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -1880,6 +1880,10 @@ i915_gem_object_move_to_active(struct drm_i915_gem_object *obj, u32 seqno = intel_ring_get_seqno(ring); BUG_ON(ring == NULL); + if (obj->ring != ring && obj->last_write_seqno) { + /* Keep the seqno relative to the current ring */ + obj->last_write_seqno = seqno; + } obj->ring = ring; /* Add a reference if we're newly entering the active list. */