sync: always set the brackets (#59644)
The current code sets bracket_greater to the first trigger after the current value, and bracket_less to the last trigger before the current value. For example, the idle timer with three negative and three positive transitions would set this: nt1 nt2 nt3 |--------|------|--|------- idle --|---|--|-----> t pt1 pt2 pt3 bracket_less == nt2 bracket_greater == pt2 This is an optimization so we can skip code paths in the block/wakeup handlers if the current value doesn't meet any of the trigger requirements. Those handlers largely do a if (bracket_less is less than current value && bracket_greater is greater than current value) return, nothing to do However, unless the bracket values are updated at the correct time, the following may happen: nt |--------------|---------- idle ------|--------> t pt In this case, neither bracket is set, we're past the pos transition and not yet at the neg transition. idle may now go past nt, but the brackets are not updated. If idle is then reset to 0, no alarm is triggered for nt. Likewise, idle may now go past pt and no alarm is triggered. Changing an alarm or triggering an alarm will re-calculate the brackets, so this bug is somewhat random. If any other client triggers an alarm when the brackets are wrongly NULL, the recalculation will set them this bug may not appear. This patch changes the behavior, so that the brackets are always the nearest positive or negative transitions to the current counter value. In the example above, nt will trigger a wakeup and a re-calculation of the brackets, so that going past it in the negative direction will then cause the proper alarm triggers. Or, in Keith's words: Timer currently past a positive trigger No bracket values, because no trigger in range Timer moves backwards before the positive trigger Brackets not reset, even though there is now a trigger in range Timer moves forward past the positive trigger Trigger doesn't fire because brackets not set Setting the LT bracket in this case will cause everything to get re-evaluated when the sync value moves backwards before the trigger value. X.Org Bug 59644 <http://bugs.freedesktop.org/show_bug.cgi?id=59644> Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net> Reviewed-by: Adam Jackson <ajax@redhat.com> Reviewed-by: Keith Packard <keithp@keithp.com>
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Xext/sync.c
20
Xext/sync.c
@ -1019,6 +1019,11 @@ SyncComputeBracketValues(SyncCounter * pCounter)
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psci->bracket_greater = pTrigger->test_value;
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pnewgtval = &psci->bracket_greater;
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}
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else if (XSyncValueGreaterThan(pCounter->value, pTrigger->test_value) &&
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XSyncValueGreaterThan(pTrigger->test_value, psci->bracket_less)) {
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psci->bracket_less = pTrigger->test_value;
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pnewltval = &psci->bracket_less;
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}
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}
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else if (pTrigger->test_type == XSyncNegativeComparison &&
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ct != XSyncCounterNeverDecreases) {
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@ -1028,6 +1033,11 @@ SyncComputeBracketValues(SyncCounter * pCounter)
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psci->bracket_less = pTrigger->test_value;
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pnewltval = &psci->bracket_less;
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}
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else if (XSyncValueLessThan(pCounter->value, pTrigger->test_value) &&
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XSyncValueLessThan(pTrigger->test_value, psci->bracket_greater)) {
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psci->bracket_greater = pTrigger->test_value;
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pnewgtval = &psci->bracket_greater;
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}
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}
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else if (pTrigger->test_type == XSyncNegativeTransition &&
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ct != XSyncCounterNeverIncreases) {
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@ -1041,6 +1051,11 @@ SyncComputeBracketValues(SyncCounter * pCounter)
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psci->bracket_less = pTrigger->test_value;
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pnewltval = &psci->bracket_less;
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}
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else if (XSyncValueLessThan(pCounter->value, pTrigger->test_value) &&
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XSyncValueLessThan(pTrigger->test_value, psci->bracket_greater)) {
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psci->bracket_greater = pTrigger->test_value;
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pnewgtval = &psci->bracket_greater;
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}
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}
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else if (pTrigger->test_type == XSyncPositiveTransition &&
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ct != XSyncCounterNeverDecreases) {
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@ -1055,6 +1070,11 @@ SyncComputeBracketValues(SyncCounter * pCounter)
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psci->bracket_greater = pTrigger->test_value;
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pnewgtval = &psci->bracket_greater;
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}
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else if (XSyncValueGreaterThan(pCounter->value, pTrigger->test_value) &&
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XSyncValueGreaterThan(pTrigger->test_value, psci->bracket_less)) {
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psci->bracket_less = pTrigger->test_value;
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pnewltval = &psci->bracket_less;
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}
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}
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} /* end for each trigger */
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