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- Fix several bugs in the rundown protection implementation, mostly related to incorrect loop restarting in case of a race condition.

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- The rundown event is a sync event, not a notification event.
- Only take slow path when waiting for release if the value changed *and* is still not active, not if only one of the two is true.

svn path=/trunk/; revision=25472
This commit is contained in:
Alex Ionescu
2007-01-15 21:12:32 +00:00
parent 6b4b2a47a3
commit 2e03cf0bb5
2 changed files with 76 additions and 68 deletions
Download Patch File Download Diff File Expand all files Collapse all files
reactos/ntoskrnl/ex/rundown.c
+69 -61
View File
@@ -36,21 +36,21 @@ ExfAcquireRundownProtection(IN PEX_RUNDOWN_REF RunRef)
{
ULONG_PTR Value = RunRef->Count, NewValue;
/* Make sure a rundown is not active */
if (Value & EX_RUNDOWN_ACTIVE) return FALSE;
/* Loop until successfully incremented the counter */
for (;;)
{
/* Make sure a rundown is not active */
if (Value & EX_RUNDOWN_ACTIVE) return FALSE;
/* Add a reference */
NewValue = Value + EX_RUNDOWN_COUNT_INC;
/* Change the value */
Value = ExpChangeRundown(RunRef, NewValue, Value);
if (Value == NewValue) return TRUE;
NewValue = ExpChangeRundown(RunRef, NewValue, Value);
if (NewValue == Value) return TRUE;
/* Make sure a rundown is not active */
if (Value & EX_RUNDOWN_ACTIVE) return FALSE;
/* Update it */
Value = NewValue;
}
}
@@ -79,24 +79,21 @@ ExfAcquireRundownProtectionEx(IN PEX_RUNDOWN_REF RunRef,
{
ULONG_PTR Value = RunRef->Count, NewValue;
/* Make sure a rundown is not active */
if (Value & EX_RUNDOWN_ACTIVE) return FALSE;
/* Convert the count to our internal representation */
Count <<= EX_RUNDOWN_COUNT_SHIFT;
/* Loop until successfully incremented the counter */
for (;;)
{
/* Add references */
NewValue = Value + Count;
/* Change the value */
Value = ExpChangeRundown(RunRef, NewValue, Value);
if (Value == NewValue) return TRUE;
/* Make sure a rundown is not active */
if (Value & EX_RUNDOWN_ACTIVE) return FALSE;
/* Add references */
NewValue = Value + EX_RUNDOWN_COUNT_INC * Count;
/* Change the value */
NewValue = ExpChangeRundown(RunRef, NewValue, Value);
if (NewValue == Value) return TRUE;
/* Update the value */
Value = NewValue;
}
}
@@ -201,11 +198,11 @@ ExfReleaseRundownProtection(IN PEX_RUNDOWN_REF RunRef)
ULONG_PTR Value = RunRef->Count, NewValue;
PEX_RUNDOWN_WAIT_BLOCK WaitBlock;
/* Check if rundown is not active */
if (!(Value & EX_RUNDOWN_ACTIVE))
/* Loop until successfully incremented the counter */
for (;;)
{
/* Loop until successfully incremented the counter */
for (;;)
/* Check if rundown is not active */
if (!(Value & EX_RUNDOWN_ACTIVE))
{
/* Sanity check */
ASSERT((Value >= EX_RUNDOWN_COUNT_INC) || (KeNumberProcessors > 1));
@@ -214,23 +211,28 @@ ExfReleaseRundownProtection(IN PEX_RUNDOWN_REF RunRef)
NewValue = Value - EX_RUNDOWN_COUNT_INC;
/* Change the value */
Value = ExpChangeRundown(RunRef, NewValue, Value);
if (Value == NewValue) return;
NewValue = ExpChangeRundown(RunRef, NewValue, Value);
if (NewValue == Value) break;
/* Loop again if we're still not active */
if (Value & EX_RUNDOWN_ACTIVE) break;
/* Update value */
Value = NewValue;
}
}
else
{
/* Get the wait block */
WaitBlock = (PEX_RUNDOWN_WAIT_BLOCK)(Value & ~EX_RUNDOWN_ACTIVE);
ASSERT((WaitBlock->Count > 0) || (KeNumberProcessors > 1));
/* Get the wait block */
WaitBlock = (PEX_RUNDOWN_WAIT_BLOCK)(Value & ~EX_RUNDOWN_ACTIVE);
ASSERT((WaitBlock->Count > 0) || (KeNumberProcessors > 1));
/* Remove the one count */
if (!InterlockedDecrementSizeT(&WaitBlock->Count))
{
/* We're down to 0 now, so signal the event */
KeSetEvent(&WaitBlock->WakeEvent, IO_NO_INCREMENT, FALSE);
}
/* Remove the one count */
if (!InterlockedDecrementSizeT(&WaitBlock->Count))
{
/* We're down to 0 now, so signal the event */
KeSetEvent(&WaitBlock->WakeEvent, IO_NO_INCREMENT, FALSE);
/* We're all done */
break;
}
}
}
@@ -260,37 +262,43 @@ ExfReleaseRundownProtectionEx(IN PEX_RUNDOWN_REF RunRef,
ULONG_PTR Value = RunRef->Count, NewValue;
PEX_RUNDOWN_WAIT_BLOCK WaitBlock;
/* Check if rundown is not active */
if (!(Value & EX_RUNDOWN_ACTIVE))
/* Loop until successfully incremented the counter */
for (;;)
{
/* Loop until successfully incremented the counter */
for (;;)
/* Check if rundown is not active */
if (!(Value & EX_RUNDOWN_ACTIVE))
{
/* Sanity check */
ASSERT((Value >= EX_RUNDOWN_COUNT_INC * Count) || (KeNumberProcessors > 1));
ASSERT((Value >= EX_RUNDOWN_COUNT_INC * Count) ||
(KeNumberProcessors > 1));
/* Get the new value */
NewValue = Value - (Count * EX_RUNDOWN_COUNT_INC);
NewValue = Value - EX_RUNDOWN_COUNT_INC * Count;
/* Change the value */
Value = ExpChangeRundown(RunRef, NewValue, Value);
if (Value == NewValue) return;
NewValue = ExpChangeRundown(RunRef, NewValue, Value);
if (NewValue == Value) break;
/* Loop again if we're still not active */
if (Value & EX_RUNDOWN_ACTIVE) break;
/* Update value */
Value = NewValue;
}
}
else
{
/* Get the wait block */
WaitBlock = (PEX_RUNDOWN_WAIT_BLOCK)(Value & ~EX_RUNDOWN_ACTIVE);
ASSERT((WaitBlock->Count >= Count) || (KeNumberProcessors > 1));
/* Get the wait block */
WaitBlock = (PEX_RUNDOWN_WAIT_BLOCK)(Value & ~EX_RUNDOWN_ACTIVE);
ASSERT((WaitBlock->Count >= Count) || (KeNumberProcessors > 1));
/* Remove the counts */
if (InterlockedExchangeAddSizeT(&WaitBlock->Count,
-(LONG)Count) == (LONG)Count)
{
/* We're down to 0 now, so signal the event */
KeSetEvent(&WaitBlock->WakeEvent, IO_NO_INCREMENT, FALSE);
}
/* Remove the count */
if (InterlockedExchangeAddSizeT(&WaitBlock->Count, -(LONG)Count) ==
(LONG)Count)
{
/* We're down to 0 now, so signal the event */
KeSetEvent(&WaitBlock->WakeEvent, IO_NO_INCREMENT, FALSE);
/* We're all done */
break;
}
}
}
@@ -330,17 +338,17 @@ ExfWaitForRundownProtectionRelease(IN PEX_RUNDOWN_REF RunRef)
EX_RUNDOWN_ACTIVE);
/* Start waitblock set loop */
for(;;)
for (;;)
{
/* Save the count */
Count = Value >> EX_RUNDOWN_COUNT_SHIFT;
/* If the count is over one or we don't have en event yet, create it */
if (Count || !Event)
/* If the count is over one and we don't have en event yet, create it */
if ((Count) && !(Event))
{
/* Initialize the event */
KeInitializeEvent(&WaitBlock.WakeEvent,
NotificationEvent,
SynchronizationEvent,
FALSE);
/* Set the pointer */
reactos/ntoskrnl/include/internal/ex.h
+7 -7
View File
@@ -364,7 +364,7 @@ BOOLEAN
FORCEINLINE
_ExAcquireRundownProtection(IN PEX_RUNDOWN_REF RunRef)
{
ULONG_PTR Value, NewValue, OldValue;
ULONG_PTR Value, NewValue;
/* Get the current value and mask the active bit */
Value = RunRef->Count &~ EX_RUNDOWN_ACTIVE;
@@ -373,8 +373,8 @@ _ExAcquireRundownProtection(IN PEX_RUNDOWN_REF RunRef)
NewValue = Value + EX_RUNDOWN_COUNT_INC;
/* Change the value */
OldValue = ExpChangeRundown(RunRef, NewValue, Value);
if (OldValue != Value)
NewValue = ExpChangeRundown(RunRef, NewValue, Value);
if (NewValue != Value)
{
/* Rundown was active, use long path */
return ExfAcquireRundownProtection(RunRef);
@@ -405,7 +405,7 @@ VOID
FORCEINLINE
_ExReleaseRundownProtection(IN PEX_RUNDOWN_REF RunRef)
{
ULONG_PTR Value, NewValue, OldValue;
ULONG_PTR Value, NewValue;
/* Get the current value and mask the active bit */
Value = RunRef->Count &~ EX_RUNDOWN_ACTIVE;
@@ -414,10 +414,10 @@ _ExReleaseRundownProtection(IN PEX_RUNDOWN_REF RunRef)
NewValue = Value - EX_RUNDOWN_COUNT_INC;
/* Change the value */
OldValue = ExpChangeRundown(RunRef, NewValue, Value);
NewValue = ExpChangeRundown(RunRef, NewValue, Value);
/* Check if the rundown was active */
if (OldValue != Value)
if (NewValue != Value)
{
/* Rundown was active, use long path */
ExfReleaseRundownProtection(RunRef);
@@ -476,7 +476,7 @@ _ExWaitForRundownProtectionRelease(IN PEX_RUNDOWN_REF RunRef)
/* Set the active bit */
Value = ExpChangeRundown(RunRef, EX_RUNDOWN_ACTIVE, 0);
if ((Value) || (Value != EX_RUNDOWN_ACTIVE))
if ((Value) && (Value != EX_RUNDOWN_ACTIVE))
{
/* If the the rundown wasn't already active, then take the long path */
ExfWaitForRundownProtectionRelease(RunRef);