6a3800f611
Task A holds an IOB. There are no further IOBs. The value of semcount is zero. Task B calls iob_alloc(). Since there are not IOBs, it calls sem_wait(). The v alue of semcount is now -1. Task A frees the IOB. iob_free() adds the IOB to the free list and calls sem_post() this makes Task B ready to run and sets semcount to zero NOT 1. There is one IOB in the free list and semcount is zero. When Task B wakes up it would increment the sem_count back to the correct value. But an interrupt or another task runs occurs before Task B executes. The interrupt or other tak takes the IOB off of the free list and decrements the semcount. But since semcount is then < 0, this causes the assertion because that is an invalid state in the interrupt handler. So I think that the root cause is that there the asynchrony between incrementing the semcount. This change separates the list of IOBs: Currently there is only a free list of IOBs. The problem, I believe, is because of asynchronies due sem_post() post cause the semcount and the list content to become out of sync. This change adds a new 'committed' list: When there is a task waiting for an IOB, it will go into the committed list rather than the free list before the semaphore is posted. On the waiting side, when awakened from the semaphore wait, it will expect to find its IOB in the committed list, rather than free list. In this way, the content of the free list and the value of the semaphore count always remain in sync.
145 lines
4.8 KiB
C
145 lines
4.8 KiB
C
/****************************************************************************
|
|
* mm/iob/iob_free.c
|
|
*
|
|
* Copyright (C) 2014, 2016-2017 Gregory Nutt. All rights reserved.
|
|
* Author: Gregory Nutt <gnutt@nuttx.org>
|
|
*
|
|
* Redistribution and use in source and binary forms, with or without
|
|
* modification, are permitted provided that the following conditions
|
|
* are met:
|
|
*
|
|
* 1. Redistributions of source code must retain the above copyright
|
|
* notice, this list of conditions and the following disclaimer.
|
|
* 2. Redistributions in binary form must reproduce the above copyright
|
|
* notice, this list of conditions and the following disclaimer in
|
|
* the documentation and/or other materials provided with the
|
|
* distribution.
|
|
* 3. Neither the name NuttX nor the names of its contributors may be
|
|
* used to endorse or promote products derived from this software
|
|
* without specific prior written permission.
|
|
*
|
|
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
|
|
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
|
|
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
|
|
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
|
|
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
|
|
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
|
|
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
|
|
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
|
|
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
|
|
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
|
|
* POSSIBILITY OF SUCH DAMAGE.
|
|
*
|
|
****************************************************************************/
|
|
|
|
/****************************************************************************
|
|
* Included Files
|
|
****************************************************************************/
|
|
|
|
#include <nuttx/config.h>
|
|
|
|
#include <semaphore.h>
|
|
#include <assert.h>
|
|
#include <debug.h>
|
|
|
|
#include <nuttx/irq.h>
|
|
#include <nuttx/arch.h>
|
|
#include <nuttx/mm/iob.h>
|
|
|
|
#include "iob.h"
|
|
|
|
/****************************************************************************
|
|
* Public Functions
|
|
****************************************************************************/
|
|
|
|
/****************************************************************************
|
|
* Name: iob_free
|
|
*
|
|
* Description:
|
|
* Free the I/O buffer at the head of a buffer chain returning it to the
|
|
* free list. The link to the next I/O buffer in the chain is return.
|
|
*
|
|
****************************************************************************/
|
|
|
|
FAR struct iob_s *iob_free(FAR struct iob_s *iob)
|
|
{
|
|
FAR struct iob_s *next = iob->io_flink;
|
|
irqstate_t flags;
|
|
|
|
iobinfo("iob=%p io_pktlen=%u io_len=%u next=%p\n",
|
|
iob, iob->io_pktlen, iob->io_len, next);
|
|
|
|
/* Copy the data that only exists in the head of a I/O buffer chain into
|
|
* the next entry.
|
|
*/
|
|
|
|
if (next != NULL)
|
|
{
|
|
/* Copy and decrement the total packet length, being careful to
|
|
* do nothing too crazy.
|
|
*/
|
|
|
|
if (iob->io_pktlen > iob->io_len)
|
|
{
|
|
/* Adjust packet length and move it to the next entry */
|
|
|
|
next->io_pktlen = iob->io_pktlen - iob->io_len;
|
|
DEBUGASSERT(next->io_pktlen >= next->io_len);
|
|
}
|
|
else
|
|
{
|
|
/* This can only happen if the next entry is last entry in the
|
|
* chain... and if it is empty
|
|
*/
|
|
|
|
next->io_pktlen = 0;
|
|
DEBUGASSERT(next->io_len == 0 && next->io_flink == NULL);
|
|
}
|
|
|
|
iobinfo("next=%p io_pktlen=%u io_len=%u\n",
|
|
next, next->io_pktlen, next->io_len);
|
|
}
|
|
|
|
/* Free the I/O buffer by adding it to the head of the free or the
|
|
* committed list. We don't know what context we are called from so
|
|
* we use extreme measures to protect the free list: We disable
|
|
* interrupts very briefly.
|
|
*/
|
|
|
|
flags = enter_critical_section();
|
|
|
|
/* Which list? If there is a task waiting for an IOB, then put
|
|
* the IOB on either the free list or on the committed list where
|
|
* it is reserved for that allocation (and not available to
|
|
* iob_tryalloc()).
|
|
*/
|
|
|
|
if (g_iob_sem.semcount < 0)
|
|
{
|
|
iob->io_flink = g_iob_committed;
|
|
g_iob_committed = iob;
|
|
}
|
|
else
|
|
{
|
|
iob->io_flink = g_iob_freelist;
|
|
g_iob_freelist = iob;
|
|
}
|
|
|
|
/* Signal that an IOB is available. If there is a thread waiting
|
|
* for an IOB, this will wake up exactly one thread. The semaphore
|
|
* count will correctly indicated that the awakened task owns an
|
|
* IOB and should find it in the committed list.
|
|
*/
|
|
|
|
sem_post(&g_iob_sem);
|
|
#if CONFIG_IOB_THROTTLE > 0
|
|
sem_post(&g_throttle_sem);
|
|
#endif
|
|
leave_critical_section(flags);
|
|
|
|
/* And return the I/O buffer after the one that was freed */
|
|
|
|
return next;
|
|
}
|