Nyaaori/rockbox
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity

Certain data accesses in the kernel should have volatile semantics to be correct and not rely on the whims of the compiler. Change queue clearing to simply catch read up to write rather than reset both to 0 to ensure sane results for queue_count and queue_empty with concurrency. Binsize may or may not increase a bit depending upon whether the output was as intended in all places; wrong stuff was already unlikely to cause any issue.

Browse source 
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@28909 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Michael Sevakis 2010-12-27 10:05:09 +00:00
parent 479414facc
commit 7b4eb44395
3 changed files with 54 additions and 38 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

10
firmware/export/kernel.h
View file

@ -106,7 +106,7 @@ struct queue_sender_list
struct thread_entry *senders[QUEUE_LENGTH]; /* message->thread map */
struct thread_entry *list; /* list of senders in map */
/* Send info for last message dequeued or NULL if replied or not sent */
struct thread_entry *curr_sender;
struct thread_entry * volatile curr_sender;
#ifdef HAVE_PRIORITY_SCHEDULING
struct blocker blocker;
#endif
@ -126,10 +126,10 @@ struct event_queue
{
struct thread_entry *queue; /* waiter list */
struct queue_event events[QUEUE_LENGTH]; /* list of events */
unsigned int read; /* head of queue */
unsigned int write; /* tail of queue */
unsigned int volatile read; /* head of queue */
unsigned int volatile write; /* tail of queue */
#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
struct queue_sender_list *send; /* list of threads waiting for
struct queue_sender_list * volatile send; /* list of threads waiting for
reply to an event */
#ifdef HAVE_PRIORITY_SCHEDULING
struct blocker *blocker_p; /* priority inheritance info
@ -171,7 +171,7 @@ struct semaphore
struct wakeup
{
struct thread_entry *queue; /* waiter list */
bool signalled; /* signalled status */
bool volatile signalled; /* signalled status */
IF_COP( struct corelock cl; ) /* multiprocessor sync */
};
#endif

2
firmware/export/thread.h
View file

@ -269,7 +269,7 @@ struct thread_entry
/* Only enabled when using queue_send for now */
#endif
#if defined(HAVE_EXTENDED_MESSAGING_AND_NAME) || NUM_CORES > 1
intptr_t retval; /* Return value from a blocked operation/
volatile intptr_t retval; /* Return value from a blocked operation/
misc. use */
#endif
#ifdef HAVE_PRIORITY_SCHEDULING

80
firmware/kernel.c
View file

@ -274,7 +274,7 @@ void yield(void)
* more efficent to reject the majority of cases that don't need this
* called.
*/
static void queue_release_sender(struct thread_entry **sender,
static void queue_release_sender(struct thread_entry * volatile * sender,
intptr_t retval)
{
struct thread_entry *thread = *sender;
@ -427,8 +427,11 @@ void queue_init(struct event_queue *q, bool register_queue)
corelock_init(&q->cl);
q->queue = NULL;
q->read = 0;
q->write = 0;
/* What garbage is in write is irrelevant because of the masking design-
* any other functions the empty the queue do this as well so that
* queue_count and queue_empty return sane values in the case of a
* concurrent change without locking inside them. */
q->read = q->write;
#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
q->send = NULL; /* No message sending by default */
IF_PRIO( q->blocker_p = NULL; )
@ -484,8 +487,7 @@ void queue_delete(struct event_queue *q)
}
#endif
q->read = 0;
q->write = 0;
q->read = q->write;
corelock_unlock(&q->cl);
restore_irq(oldlevel);
@ -510,29 +512,31 @@ void queue_wait(struct event_queue *q, struct queue_event *ev)
/* auto-reply */
queue_do_auto_reply(q->send);
if (q->read == q->write)
while(1)
{
struct thread_entry *current = thread_id_entry(THREAD_ID_CURRENT);
struct thread_entry *current;
do
{
IF_COP( current->obj_cl = &q->cl; )
current->bqp = &q->queue;
rd = q->read;
if (rd != q->write) /* A waking message could disappear */
break;
block_thread(current);
current = thread_id_entry(THREAD_ID_CURRENT);
corelock_unlock(&q->cl);
switch_thread();
IF_COP( current->obj_cl = &q->cl; )
current->bqp = &q->queue;
oldlevel = disable_irq_save();
corelock_lock(&q->cl);
}
/* A message that woke us could now be gone */
while (q->read == q->write);
block_thread(current);
corelock_unlock(&q->cl);
switch_thread();
oldlevel = disable_irq_save();
corelock_lock(&q->cl);
}
rd = q->read++ & QUEUE_LENGTH_MASK;
q->read = rd + 1;
rd &= QUEUE_LENGTH_MASK;
*ev = q->events[rd];
/* Get data for a waiting thread if one */
@ -545,6 +549,7 @@ void queue_wait(struct event_queue *q, struct queue_event *ev)
void queue_wait_w_tmo(struct event_queue *q, struct queue_event *ev, int ticks)
{
int oldlevel;
unsigned int rd, wr;
#ifdef HAVE_EXTENDED_MESSAGING_AND_NAME
KERNEL_ASSERT(QUEUE_GET_THREAD(q) == NULL ||
@ -558,7 +563,9 @@ void queue_wait_w_tmo(struct event_queue *q, struct queue_event *ev, int ticks)
/* Auto-reply */
queue_do_auto_reply(q->send);
if (q->read == q->write && ticks > 0)
rd = q->read;
wr = q->write;
if (rd == wr && ticks > 0)
{
struct thread_entry *current = thread_id_entry(THREAD_ID_CURRENT);
@ -572,13 +579,17 @@ void queue_wait_w_tmo(struct event_queue *q, struct queue_event *ev, int ticks)
oldlevel = disable_irq_save();
corelock_lock(&q->cl);
rd = q->read;
wr = q->write;
}
/* no worry about a removed message here - status is checked inside
locks - perhaps verify if timeout or false alarm */
if (q->read != q->write)
if (rd != wr)
{
unsigned int rd = q->read++ & QUEUE_LENGTH_MASK;
q->read = rd + 1;
rd &= QUEUE_LENGTH_MASK;
*ev = q->events[rd];
/* Get data for a waiting thread if one */
queue_do_fetch_sender(q->send, rd);
@ -700,13 +711,16 @@ void queue_reply(struct event_queue *q, intptr_t retval)
{
if(q->send && q->send->curr_sender)
{
struct queue_sender_list *sender;
int oldlevel = disable_irq_save();
corelock_lock(&q->cl);
sender = q->send;
/* Double-check locking */
IF_COP( if(LIKELY(q->send && q->send->curr_sender)) )
{
queue_release_sender(&q->send->curr_sender, retval);
}
if(LIKELY(sender && sender->curr_sender))
queue_release_sender(&sender->curr_sender, retval);
corelock_unlock(&q->cl);
restore_irq(oldlevel);
@ -716,6 +730,8 @@ void queue_reply(struct event_queue *q, intptr_t retval)
bool queue_peek(struct event_queue *q, struct queue_event *ev)
{
unsigned int rd;
if(q->read == q->write)
return false;
@ -724,9 +740,10 @@ bool queue_peek(struct event_queue *q, struct queue_event *ev)
int oldlevel = disable_irq_save();
corelock_lock(&q->cl);
if(q->read != q->write)
rd = q->read;
if(rd != q->write)
{
*ev = q->events[q->read & QUEUE_LENGTH_MASK];
*ev = q->events[rd & QUEUE_LENGTH_MASK];
have_msg = true;
}
@ -756,8 +773,7 @@ void queue_clear(struct event_queue* q)
dequeued sent message will be handled by owning thread */
queue_release_all_senders(q);
q->read = 0;
q->write = 0;
q->read = q->write;
corelock_unlock(&q->cl);
restore_irq(oldlevel);