Fix race condition when semaphore wait is interrupted by a signl
git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@2935 42af7a65-404d-4744-a932-0658087f49c3
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@ -1274,3 +1274,8 @@
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reading from offsets into this file that correspond to virtual
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fault addresses. up_fillpage.c implements logic to perform page
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files using the CONFIG_PAGING_BINPATH file.
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* configs/mbed - Add configuration to support the mbed.org LPC1768
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board (Contributed by Dave Marples).
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* sched/sem_wait.c and sem_waitirq.c - Eliminate a race condition
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that can occur when a semaphore wait is interrupt by a signal.
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(see email thread: http://tech.groups.yahoo.com/group/nuttx/message/530)
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@ -8,7 +8,7 @@
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<tr align="center" bgcolor="#e4e4e4">
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<td>
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<h1><big><font color="#3c34ec"><i>NuttX RTOS</i></font></big></h1>
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<p>Last Updated: September 8, 2010</p>
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<p>Last Updated: September 9, 2010</p>
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</td>
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</tr>
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</table>
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@ -1262,10 +1262,19 @@
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<td>
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<p>
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<b>NXP LPC1768</b>.
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This port uses the Nucleus 2G board from <a href="http://www.2g-eng.com/">2G Engineering</a>
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featuring the NXP LPC1768 MCU.
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This port uses a GNU arm-elf or arm-eabi toolchain* under either Linux or Cygwin (with native Windows GNU
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tools or Cygwin-based GNU tools).
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Configurations are available for two boards:
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<ul>
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<li>
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The Nucleus 2G board from <a href="http://www.2g-eng.com/">2G Engineering</a>, and
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</li>
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<li>
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The mbed board from <a href="http://mbed.org">mbed.org</a> (Contributed by Dave Marples).
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</li>
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</ul>
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</p>
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<p>
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Both boards feature the NXP LPC1768 MCU and a GNU arm-elf or arm-eabi toolchain* under
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either Linux or Cygwin (with native Windows GNU tools or Cygwin-based GNU tools).
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</p>
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<ul>
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<p>
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@ -1282,6 +1291,9 @@
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However, due to some technical reasons, neither the SPI nor the USB device drivers are fully verified.
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(Although it has been reported to me that the SPI microSD is functional on other platforms).
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</p>
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<p>
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Support for the mbed board was contributed by Dave Marples and released in NuttX-5.11.
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</p>
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<p>
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<b>Development Environments:</b>
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1) Linux with native Linux GNU toolchain, 2) Cygwin with Cygwin GNU toolchain, or 3) Cygwin
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@ -1957,6 +1969,11 @@ nuttx-5.11 2010-xx-xx Gregory Nutt <spudmonkey@racsa.co.cr>
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reading from offsets into this file that correspond to virtual
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fault addresses. up_fillpage.c implements logic to perform page
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files using the CONFIG_PAGING_BINPATH file.
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* configs/mbed - Add configuration to support the mbed.org LPC1768
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board (Contributed by Dave Marples).
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* sched/sem_wait.c and sem_waitirq.c - Eliminate a race condition
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that can occur when a semaphore wait is interrupt by a signal.
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(see email thread: http://tech.groups.yahoo.com/group/nuttx/message/530)
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pascal-2.1 2010-xx-xx Gregory Nutt <spudmonkey@racsa.co.cr>
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@ -1,7 +1,7 @@
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/****************************************************************************
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* sched/sem_holder.c
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*
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* Copyright (C) 2009 Gregory Nutt. All rights reserved.
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* Copyright (C) 2009-2010 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
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*
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* Redistribution and use in source and binary forms, with or without
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@ -818,7 +818,8 @@ void sem_restorebaseprio(FAR _TCB *stcb, FAR sem_t *sem)
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* Description:
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* Called from sem_post() after a thread that was waiting for a semaphore
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* count was awakened because of a signal and the semaphore wait has been
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* canceled.
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* canceled. This function restores the correct thread priority of each
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* holder of the semaphore.
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*
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* Parameters:
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* sem - A reference to the semaphore no longer being waited for
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@ -1,7 +1,7 @@
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/****************************************************************************
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* sched/sem_wait.c
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*
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* Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
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* Copyright (C) 2007-2010 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
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*
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* Redistribution and use in source and binary forms, with or without
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@ -178,6 +178,20 @@ int sem_wait(FAR sem_t *sem)
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* assigned to this thread of execution, or (2) the semaphore wait
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* has been interrupted by a signal. We can detect the latter case
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* be examining the errno value.
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*
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* In the event that the semaphore wait was interrupt was interrupted
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* by a signal, certain semaphore clean-up operations have already been
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* performed (see sem_waitirq.c). Specifically:
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*
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* - sem_canceled() was called to restore the priority of all threads
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* that hold a reference to the semaphore,
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* - The semaphore count was decremented, and
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* - tcb->waitsem was nullifed.
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*
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* It is necesaary to do these things in sem_waitirq.c because a long
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* time may elapse between the time that the signal was issued and
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* this thread is awakened and this leaves a door open to several
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* race conditions.
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*/
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if (errno != EINTR)
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@ -187,11 +201,6 @@ int sem_wait(FAR sem_t *sem)
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sem_addholder(sem);
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ret = OK;
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}
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else
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{
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sem_canceled(sem);
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sem->semcount++;
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}
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#ifdef CONFIG_PRIORITY_INHERITANCE
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sched_unlock();
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@ -1,7 +1,7 @@
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/****************************************************************************
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* sched/sem_waitirq.c
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*
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* Copyright (C) 2007-2009 Gregory Nutt. All rights reserved.
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* Copyright (C) 2007-2010 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
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*
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* Redistribution and use in source and binary forms, with or without
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@ -107,6 +107,23 @@ void sem_waitirq(FAR _TCB *wtcb)
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if (wtcb->task_state == TSTATE_WAIT_SEM)
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{
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sem_t *sem = wtcb->waitsem;
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DEBUGASSERT(sem != NULL && sem->semcount < 0);
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/* Restore the correct priority of all threads that hold references
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* to this semaphore.
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*/
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sem_canceled(sem);
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/* And increment the count on the semaphore. This releases the
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* count that was taken by sem_post(). This count decremented
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* the semaphore count to negative and caused the thread to be
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* blocked in the first place.
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*/
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sem->semcount++;
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/* Indicate that the semaphore wait is over. */
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wtcb->waitsem = NULL;
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