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incubator-nuttx/mm/mm_heap/mm_sem.c

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/****************************************************************************
* mm/mm_heap/mm_sem.c
*
* Copyright (C) 2007-2009, 2013, 2017-2018 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 <unistd.h>
#include <errno.h>
#include <assert.h>
#include <nuttx/semaphore.h>
#include <nuttx/mm/mm.h>
#ifdef CONFIG_SMP
# include <nuttx/irq.h>
#endif
#ifdef MONITOR_MM_SEMAPHORE
# include <debug.h>
#endif
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/* Internal nxsem_* interfaces are not available in the user space in
* PROTECTED and KERNEL builds. In that context, the application semaphore
* interfaces must be used. The differences between the two sets of
* interfaces are: (1) the nxsem_* interfaces do not cause cancellation
* points and (2) they do not modify the errno variable.
*
* See additional definitions in include/nuttx/semaphore.h
*
* REVISIT: The fact that sem_wait() is a cancellation point is an issue
* and does cause a violation: It makes all of the memory management
* interfaces into cancellation points when used from user space in the
* PROTECTED and KERNEL builds.
*/
#if defined(CONFIG_BUILD_FLAT) || defined(__KERNEL__)
# define _SEM_GETERROR(r)
#else
# define _SEM_GETERROR(r) (r) = -errno
#endif
/* This is a special value that indicates that there is no holder of the
* semaphore. The valid range of PIDs is 0-32767 and any value outside of
* that range could be used (except -ESRCH which is a special return value
* from getpid())
*/
#define NO_HOLDER ((pid_t)-1)
/* Define MONITOR_MM_SEMAPHORE to enable semaphore state monitoring */
#ifdef MONITOR_MM_SEMAPHORE
# define msemerr _err
# define msemwarn _warn
# define mseminfo _info
#else
# ifdef CONFIG_CPP_HAVE_VARARGS
# define msemerr(x...)
# define msemwarn(x...)
# define mseminfo(x...)
# else
# define msemerr (void)
# define msemwarn (void)
# define mseminfo (void)
# endif
#endif
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: mm_seminitialize
*
* Description:
* Initialize the MM mutex
*
****************************************************************************/
void mm_seminitialize(FAR struct mm_heap_s *heap)
{
/* Initialize the MM semaphore to one (to support one-at-a-time access to
* private data sets).
*/
nxsem_init(&heap->mm_semaphore, 0, 1);
heap->mm_holder = NO_HOLDER;
heap->mm_counts_held = 0;
}
/****************************************************************************
* Name: mm_trysemaphore
*
* Description:
* Try to take the MM mutex. This is called only from the OS in certain
* conditions when it is necessary to have exclusive access to the memory
* manager but it is impossible to wait on a semaphore (e.g., the idle
* process when it performs its background memory cleanup).
*
****************************************************************************/
int mm_trysemaphore(FAR struct mm_heap_s *heap)
{
#ifdef CONFIG_SMP
irqstate_t flags = enter_critical_section();
#endif
pid_t my_pid = getpid();
int ret;
/* getpid() returns the task ID of the task at the head of the ready-to-
* run task list. mm_trysemaphore() may be called during context
* switches. There are certain situations during context switching when
* the OS data structures are in flux and where the current task (i.e.,
* the task at the head of the ready-to-run task list) is not actually
* running. Granting the semaphore access in that case is known to result
* in heap corruption as in the following failure scenario.
*
* ---------------------------- -------------------------------
* TASK A TASK B
* ---------------------------- -------------------------------
* Begins memory allocation.
* - Holder is set to TASK B
* <---- Task B preempted, Task A runs
* Task A exits
* - Current task set to Task B
* Free tcb and stack memory
* - Since holder is Task B,
* memory manager is re-
* entered, and
* - Heap is corrupted.
* ---------------------------- -------------------------------
*
* This is handled by getpid(): If the case where Task B is not actually
* running, then getpid() will return the special value -ESRCH. That will
* avoid taking the fatal 'if' logic and will fall through to use the
* 'else', albeit with a nonsensical PID value.
*/
if (my_pid < 0)
{
ret = my_pid;
goto errout;
}
/* Does the current task already hold the semaphore? Is the current
* task actually running?
*/
if (heap->mm_holder == my_pid)
{
/* Yes, just increment the number of references held by the current
* task.
*/
heap->mm_counts_held++;
ret = OK;
}
else
{
/* Try to take the semaphore */
ret = _SEM_TRYWAIT(&heap->mm_semaphore);
if (ret < 0)
{
_SEM_GETERROR(ret);
goto errout;
}
/* We have it. Claim the heap for the current task and return */
heap->mm_holder = my_pid;
heap->mm_counts_held = 1;
ret = OK;
}
errout:
#ifdef CONFIG_SMP
leave_critical_section(flags);
#endif
return ret;
}
/****************************************************************************
* Name: mm_takesemaphore
*
* Description:
* Take the MM mutex. This is the normal action before all memory
* management actions.
*
****************************************************************************/
void mm_takesemaphore(FAR struct mm_heap_s *heap)
{
#ifdef CONFIG_SMP
irqstate_t flags = enter_critical_section();
#endif
pid_t my_pid = getpid();
/* Does the current task already hold the semaphore? */
if (heap->mm_holder == my_pid)
{
/* Yes, just increment the number of references held by the current
* task.
*/
heap->mm_counts_held++;
}
else
{
int ret;
/* Take the semaphore (perhaps waiting) */
mseminfo("PID=%d taking\n", my_pid);
do
{
ret = _SEM_WAIT(&heap->mm_semaphore);
/* The only case that an error should occur here is if the wait
* was awakened by a signal.
*/
if (ret < 0)
{
#if defined(CONFIG_BUILD_FLAT) || defined(__KERNEL__)
DEBUGASSERT(ret == -EINTR || ret == -ECANCELED);
#else
int errcode = get_errno();
DEBUGASSERT(errcode == EINTR || errcode == ECANCELED);
ret = -errcode;
#endif
}
}
while (ret == -EINTR);
/* We have it (or some awful, unexpected error occurred). Claim
* the semaphore for the current task and return.
*/
heap->mm_holder = my_pid;
heap->mm_counts_held = 1;
}
#ifdef CONFIG_SMP
leave_critical_section(flags);
#endif
mseminfo("Holder=%d count=%d\n", heap->mm_holder, heap->mm_counts_held);
}
/****************************************************************************
* Name: mm_givesemaphore
*
* Description:
* Release the MM mutex when it is not longer needed.
*
****************************************************************************/
void mm_givesemaphore(FAR struct mm_heap_s *heap)
{
#ifdef CONFIG_SMP
irqstate_t flags = enter_critical_section();
#endif
/* The current task should be holding at least one reference to the
* semaphore.
*/
DEBUGASSERT(heap->mm_holder == getpid());
/* Does the current task hold multiple references to the semaphore */
if (heap->mm_counts_held > 1)
{
/* Yes, just release one count and return */
heap->mm_counts_held--;
mseminfo("Holder=%d count=%d\n", heap->mm_holder,
heap->mm_counts_held);
}
else
{
/* Nope, this is the last reference held by the current task. */
mseminfo("PID=%d giving\n", getpid());
heap->mm_holder = NO_HOLDER;
heap->mm_counts_held = 0;
DEBUGVERIFY(_SEM_POST(&heap->mm_semaphore));
}
#ifdef CONFIG_SMP
leave_critical_section(flags);
#endif
}
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