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/****************************************************************************
* sched/pg_miss.c
*
* Copyright (C) 2010 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 <errno.h>
#include <debug.h>
#include <nuttx/arch.h>
#include <nuttx/sched.h>
#include <nuttx/page.h>
#ifdef CONFIG_PAGING
#include "os_internal.h"
#include "pg_internal.h"
/****************************************************************************
* Global Functions
****************************************************************************/
/****************************************************************************
* Name: pg_miss
*
* Description:
* This function is called from architecture-specific memory segmentation
* fault handling logic. This function will perform the following
* operations:
*
* 1) Sanity checking.
* - ASSERT if the currently executing task is the page fill worker
* thread. The page fill worker thread is how the the page fault
* is resolved and all logic associated with the page fill worker
* must be "locked" and always present in memory.
* - ASSERT if an interrupt was executing at the time of the exception.
* 2) Block the currently executing task.
* - Call up_block_task() to block the task at the head of the ready-
* to-run list. This should cause an interrupt level context switch
* to the next highest priority task.
* - The blocked task will be marked with state TSTATE_WAIT_PAGEFILL
* and will be retained in the g_waitingforfill prioritized task
* list.
* 3) Boost the page fill worker thread priority.
* - Check the priority of the task at the head of the g_waitingforfill
* list. If the priority of that task is higher than the current
* priority of the page fill worker thread, then boost the priority
* of the page fill worker thread to that priority.
* 4) Signal the page fill worker thread.
* - Is there a page fill pending? If not then signal the worker
* thread to start working on the queued page fill requests.
*
* Input Parameters:
* None - The head of the ready-to-run list is assumed to be task that
* caused the exception.
*
* Returned Value:
* None - Either this function function succeeds or an assertion occurs.
*
* Assumptions:
* - It is assumed that this function is called from the level of an
* exception handler and that all interrupts are disabled.
* - It is assumed that currently executing task (the one at the head of
* the ready-to-run list) is the one that cause the fault. This will
* always be true unless the page fault occurred in an interrupt handler.
* Interrupt handling logic must always be present and "locked" into
* memory.
* - As mentioned above, the task causing the page fault must not be the
* page fill worker thread because that is the only way to complete the
* page fill.
*
* NOTES:
* 1. One way to accomplish this would be a two pass link phase:
* - In the first phase, create a partially linked objected containing
* all interrupt/exception handling logic, the page fill worker thread
* plus all parts of the IDLE thread (which must always be available
* for execution).
* - All of the .text and .rodata sections of this partial link should
* be collected into a single section.
* - The second link would link the partially linked object along with
* the remaining object to produce the final binary. The linker
* script should position the "special" section so that it lies
* in a reserved, "non-swappable" region.
*
****************************************************************************/
void pg_miss(void)
{
FAR struct tcb_s *ftcb = (FAR struct tcb_s*)g_readytorun.head;
FAR struct tcb_s *wtcb;
/* Sanity checking
*
* ASSERT if the currently executing task is the page fill worker thread.
* The page fill worker thread is how the the page fault is resolved and
* all logic associated with the page fill worker must be "locked" and
* always present in memory.
*/
pglldbg("Blocking TCB: %p PID: %d\n", ftcb, ftcb->pid);
DEBUGASSERT(g_pgworker != ftcb->pid);
/* Block the currently executing task
* - Call up_block_task() to block the task at the head of the ready-
* to-run list. This should cause an interrupt level context switch
* to the next highest priority task.
* - The blocked task will be marked with state TSTATE_WAIT_PAGEFILL
* and will be retained in the g_waitingforfill prioritized task list.
*/
up_block_task(ftcb, TSTATE_WAIT_PAGEFILL);
/* Boost the page fill worker thread priority.
* - Check the priority of the task at the head of the g_waitingforfill
* list. If the priority of that task is higher than the current
* priority of the page fill worker thread, then boost the priority
* of the page fill worker thread to that priority.
*/
wtcb = sched_gettcb(g_pgworker);
DEBUGASSERT(wtcb != NULL);
if (wtcb->sched_priority < ftcb->sched_priority)
{
/* Reprioritize the page fill worker thread */
pgllvdbg("New worker priority. %d->%d\n",
wtcb->sched_priority, ftcb->sched_priority);
sched_setpriority(wtcb, ftcb->sched_priority);
}
/* Signal the page fill worker thread.
* - Is there a page fill pending? If not then signal the worker
* thread to start working on the queued page fill requests.
*/
if (!g_pftcb)
{
pglldbg("Signaling worker. PID: %d\n", g_pgworker);
kill(g_pgworker, SIGWORK);
}
}
#endif /* CONFIG_PAGING */
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