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Fix unreachable trigger level validation for stream batching buffers

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A stream batching buffer only unblocks a waiting reader when the number
of bytes in the buffer becomes strictly greater than its trigger level
(prvBytesInBufferMeetTriggerLevel), unlike a plain stream/message buffer
which unblocks when the byte count is greater than or equal to the
trigger level. The maximum number of bytes any of these buffers can
ever hold is one less than their internal length (a full/empty ring
buffer ambiguity).

The trigger-level validation in xStreamBufferGenericCreate(),
xStreamBufferGenericCreateStatic() and xStreamBufferSetTriggerLevel()
did not account for this difference: it accepted a trigger level equal
to the buffer's maximum achievable occupancy for batching buffers too.
Once such a trigger level was set, the buffer could never satisfy its
own wake predicate, so a reader blocked in xStreamBufferReceive() would
hang forever even after the buffer was completely filled.

Add a batching-buffer-specific bound at all three validation sites so
the trigger level is rejected (via configASSERT, or pdFALSE from
xStreamBufferSetTriggerLevel) when it can never be exceeded. Plain
stream and message buffers are unaffected.

Verified by compiling the affected tasks.c/list.c/stream_buffer.c
against the POSIX/GCC simulator port and running real FreeRTOS tasks:
before the fix, a batching buffer created with
xStreamBatchingBufferCreate(25, 25) hangs a reader forever even when
the writer fills all 25 bytes; after the fix, the same call is rejected
by configASSERT at creation time, while the correct boundary
(trigger = 24) and plain stream/message buffers keep working exactly
as before.

Signed-off-by: 94xhn <94xhn1@gmail.com>
Signed-off-by: 94xhn <87560781+94xhn@users.noreply.github.com>
This commit is contained in:
94xhn 2026-07-12 02:04:06 +08:00
parent 9db704cd3b
commit 357913bb8f
1 changed files with 65 additions and 11 deletions
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76
stream_buffer.c
View file

@ -371,7 +371,26 @@ static void prvInitialiseNewStreamBuffer( StreamBuffer_t * const pxStreamBuffer,
configASSERT( xBufferSizeBytes > 0 );
}
configASSERT( xTriggerLevelBytes <= xBufferSizeBytes );
/* A batching buffer only unblocks a reader when the number of bytes
* in the buffer becomes strictly greater than the trigger level (see
* prvBytesInBufferMeetTriggerLevel()), whereas a stream/message
* buffer unblocks a reader when the number of bytes is greater than
* or equal to the trigger level. The maximum number of bytes any of
* these buffers can ever hold is one less than their length (a
* full/empty ring buffer ambiguity - see prvBytesInBuffer()), which
* is compensated for non-batching buffers so xBufferSizeBytes bytes
* can be used (see the xBufferSizeBytes++ below). A batching
* buffer's trigger level must therefore be strictly less than
* xBufferSizeBytes, otherwise it could never be satisfied even when
* the buffer is completely full. */
if( ( ucFlags & sbFLAGS_IS_BATCHING_BUFFER ) != ( uint8_t ) 0 )
{
configASSERT( xTriggerLevelBytes < xBufferSizeBytes );
}
else
{
configASSERT( xTriggerLevelBytes <= xBufferSizeBytes );
}
/* A trigger level of 0 would cause a waiting task to unblock even when
* the buffer was empty. */
@ -452,14 +471,6 @@ static void prvInitialiseNewStreamBuffer( StreamBuffer_t * const pxStreamBuffer,
configASSERT( pucStreamBufferStorageArea );
configASSERT( pxStaticStreamBuffer );
configASSERT( xTriggerLevelBytes <= xBufferSizeBytes );
/* A trigger level of 0 would cause a waiting task to unblock even when
* the buffer was empty. */
if( xTriggerLevelBytes == ( size_t ) 0 )
{
xTriggerLevelBytes = ( size_t ) 1;
}
/* In case the stream buffer is going to be used as a message buffer
* (that is, it will hold discrete messages with a little meta data that
@ -484,6 +495,31 @@ static void prvInitialiseNewStreamBuffer( StreamBuffer_t * const pxStreamBuffer,
ucFlags = sbFLAGS_IS_STATICALLY_ALLOCATED;
}
/* Unlike the dynamically allocated path, a statically allocated
* buffer's xLength is exactly xBufferSizeBytes (there is no "+1"
* compensation - see xStreamBufferGenericCreate()), so the maximum
* number of bytes it can ever hold is (xBufferSizeBytes - 1). A
* batching buffer only unblocks a reader when the number of bytes in
* the buffer becomes strictly greater than the trigger level (see
* prvBytesInBufferMeetTriggerLevel()), so its trigger level must be
* strictly less than that maximum, otherwise it could never be
* satisfied even when the buffer is completely full. */
if( ( ucFlags & sbFLAGS_IS_BATCHING_BUFFER ) != ( uint8_t ) 0 )
{
configASSERT( xTriggerLevelBytes < ( xBufferSizeBytes - 1U ) );
}
else
{
configASSERT( xTriggerLevelBytes <= xBufferSizeBytes );
}
/* A trigger level of 0 would cause a waiting task to unblock even when
* the buffer was empty. */
if( xTriggerLevelBytes == ( size_t ) 0 )
{
xTriggerLevelBytes = ( size_t ) 1;
}
#if ( configASSERT_DEFINED == 1 )
{
/* Sanity check that the size of the structure used to declare a
@ -743,8 +779,26 @@ BaseType_t xStreamBufferSetTriggerLevel( StreamBufferHandle_t xStreamBuffer,
}
/* The trigger level is the number of bytes that must be in the stream
* buffer before a task that is waiting for data is unblocked. */
if( xTriggerLevel < pxStreamBuffer->xLength )
* buffer before a task that is waiting for data is unblocked. A batching
* buffer only unblocks a reader when the number of bytes in the buffer
* becomes strictly greater than the trigger level (see
* prvBytesInBufferMeetTriggerLevel()), so its trigger level must be kept
* strictly less than the maximum number of bytes the buffer can ever hold
* (xLength - 1), otherwise it could never be satisfied even when the
* buffer is completely full. */
if( ( pxStreamBuffer->ucFlags & sbFLAGS_IS_BATCHING_BUFFER ) != ( uint8_t ) 0 )
{
if( xTriggerLevel < ( pxStreamBuffer->xLength - 1U ) )
{
pxStreamBuffer->xTriggerLevelBytes = xTriggerLevel;
xReturn = pdPASS;
}
else
{
xReturn = pdFALSE;
}
}
else if( xTriggerLevel < pxStreamBuffer->xLength )
{
pxStreamBuffer->xTriggerLevelBytes = xTriggerLevel;
xReturn = pdPASS;