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ipc/sem.c: convert sem_array.sem_pending to struct list_head
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sem_array.sem_pending is a double linked list, the attached patch converts
it to struct list_head.

[[email protected]: coding-style fixes]
Signed-off-by: Manfred Spraul <[email protected]>
Reviewed-by: Nadia Derbey <[email protected]>
Cc: Pierre Peiffer <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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@manfred-colorfu @torvalds
manfred-colorfu authored and torvalds committed Jul 25, 2008
1 parent 2c0c29d commit a1193f8
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Showing 2 changed files with 40 additions and 64 deletions.
12 changes: 5 additions & 7 deletions include/linux/sem.h
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Original file line number Diff line number Diff line change
Expand Up @@ -93,21 +93,19 @@ struct sem_array {
time_t sem_otime; /* last semop time */
time_t sem_ctime; /* last change time */
struct sem *sem_base; /* ptr to first semaphore in array */
struct sem_queue *sem_pending; /* pending operations to be processed */
struct sem_queue **sem_pending_last; /* last pending operation */
struct list_head sem_pending; /* pending operations to be processed */
struct list_head list_id; /* undo requests on this array */
unsigned long sem_nsems; /* no. of semaphores in array */
};

/* One queue for each sleeping process in the system. */
struct sem_queue {
struct sem_queue * next; /* next entry in the queue */
struct sem_queue ** prev; /* previous entry in the queue, *(q->prev) == q */
struct task_struct* sleeper; /* this process */
struct sem_undo * undo; /* undo structure */
struct list_head list; /* queue of pending operations */
struct task_struct *sleeper; /* this process */
struct sem_undo *undo; /* undo structure */
int pid; /* process id of requesting process */
int status; /* completion status of operation */
struct sembuf * sops; /* array of pending operations */
struct sembuf *sops; /* array of pending operations */
int nsops; /* number of operations */
int alter; /* does the operation alter the array? */
};
Expand Down
92 changes: 35 additions & 57 deletions ipc/sem.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -272,8 +272,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
ns->used_sems += nsems;

sma->sem_base = (struct sem *) &sma[1];
/* sma->sem_pending = NULL; */
sma->sem_pending_last = &sma->sem_pending;
INIT_LIST_HEAD(&sma->sem_pending);
INIT_LIST_HEAD(&sma->list_id);
sma->sem_nsems = nsems;
sma->sem_ctime = get_seconds();
Expand Down Expand Up @@ -331,38 +330,6 @@ asmlinkage long sys_semget(key_t key, int nsems, int semflg)
return ipcget(ns, &sem_ids(ns), &sem_ops, &sem_params);
}

/* Manage the doubly linked list sma->sem_pending as a FIFO:
* insert new queue elements at the tail sma->sem_pending_last.
*/
static inline void append_to_queue (struct sem_array * sma,
struct sem_queue * q)
{
*(q->prev = sma->sem_pending_last) = q;
*(sma->sem_pending_last = &q->next) = NULL;
}

static inline void prepend_to_queue (struct sem_array * sma,
struct sem_queue * q)
{
q->next = sma->sem_pending;
*(q->prev = &sma->sem_pending) = q;
if (q->next)
q->next->prev = &q->next;
else /* sma->sem_pending_last == &sma->sem_pending */
sma->sem_pending_last = &q->next;
}

static inline void remove_from_queue (struct sem_array * sma,
struct sem_queue * q)
{
*(q->prev) = q->next;
if (q->next)
q->next->prev = q->prev;
else /* sma->sem_pending_last == &q->next */
sma->sem_pending_last = q->prev;
q->prev = NULL; /* mark as removed */
}

/*
* Determine whether a sequence of semaphore operations would succeed
* all at once. Return 0 if yes, 1 if need to sleep, else return error code.
Expand Down Expand Up @@ -438,16 +405,15 @@ static void update_queue (struct sem_array * sma)
int error;
struct sem_queue * q;

q = sma->sem_pending;
while(q) {
q = list_entry(sma->sem_pending.next, struct sem_queue, list);
while (&q->list != &sma->sem_pending) {
error = try_atomic_semop(sma, q->sops, q->nsops,
q->undo, q->pid);

/* Does q->sleeper still need to sleep? */
if (error <= 0) {
struct sem_queue *n;
remove_from_queue(sma,q);
q->status = IN_WAKEUP;

/*
* Continue scanning. The next operation
* that must be checked depends on the type of the
Expand All @@ -458,11 +424,26 @@ static void update_queue (struct sem_array * sma)
* for semaphore values to become 0.
* - if the operation didn't modify the array,
* then just continue.
* The order of list_del() and reading ->next
* is crucial: In the former case, the list_del()
* must be done first [because we might be the
* first entry in ->sem_pending], in the latter
* case the list_del() must be done last
* [because the list is invalid after the list_del()]
*/
if (q->alter)
n = sma->sem_pending;
else
n = q->next;
if (q->alter) {
list_del(&q->list);
n = list_entry(sma->sem_pending.next,
struct sem_queue, list);
} else {
n = list_entry(q->list.next, struct sem_queue,
list);
list_del(&q->list);
}

/* wake up the waiting thread */
q->status = IN_WAKEUP;

wake_up_process(q->sleeper);
/* hands-off: q will disappear immediately after
* writing q->status.
Expand All @@ -471,7 +452,7 @@ static void update_queue (struct sem_array * sma)
q->status = error;
q = n;
} else {
q = q->next;
q = list_entry(q->list.next, struct sem_queue, list);
}
}
}
Expand All @@ -491,7 +472,7 @@ static int count_semncnt (struct sem_array * sma, ushort semnum)
struct sem_queue * q;

semncnt = 0;
for (q = sma->sem_pending; q; q = q->next) {
list_for_each_entry(q, &sma->sem_pending, list) {
struct sembuf * sops = q->sops;
int nsops = q->nsops;
int i;
Expand All @@ -503,13 +484,14 @@ static int count_semncnt (struct sem_array * sma, ushort semnum)
}
return semncnt;
}

static int count_semzcnt (struct sem_array * sma, ushort semnum)
{
int semzcnt;
struct sem_queue * q;

semzcnt = 0;
for (q = sma->sem_pending; q; q = q->next) {
list_for_each_entry(q, &sma->sem_pending, list) {
struct sembuf * sops = q->sops;
int nsops = q->nsops;
int i;
Expand All @@ -529,7 +511,7 @@ static int count_semzcnt (struct sem_array * sma, ushort semnum)
static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
{
struct sem_undo *un;
struct sem_queue *q;
struct sem_queue *q, *t;
struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);

/* Invalidate the existing undo structures for this semaphore set.
Expand All @@ -541,17 +523,14 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
un->semid = -1;

/* Wake up all pending processes and let them fail with EIDRM. */
q = sma->sem_pending;
while(q) {
struct sem_queue *n;
/* lazy remove_from_queue: we are killing the whole queue */
q->prev = NULL;
n = q->next;

list_for_each_entry_safe(q, t, &sma->sem_pending, list) {
list_del(&q->list);

q->status = IN_WAKEUP;
wake_up_process(q->sleeper); /* doesn't sleep */
smp_wmb();
q->status = -EIDRM; /* hands-off q */
q = n;
}

/* Remove the semaphore set from the IDR */
Expand Down Expand Up @@ -1166,9 +1145,9 @@ asmlinkage long sys_semtimedop(int semid, struct sembuf __user *tsops,
queue.pid = task_tgid_vnr(current);
queue.alter = alter;
if (alter)
append_to_queue(sma ,&queue);
list_add_tail(&queue.list, &sma->sem_pending);
else
prepend_to_queue(sma ,&queue);
list_add(&queue.list, &sma->sem_pending);

queue.status = -EINTR;
queue.sleeper = current;
Expand All @@ -1194,7 +1173,6 @@ asmlinkage long sys_semtimedop(int semid, struct sembuf __user *tsops,

sma = sem_lock(ns, semid);
if (IS_ERR(sma)) {
BUG_ON(queue.prev != NULL);
error = -EIDRM;
goto out_free;
}
Expand All @@ -1212,7 +1190,7 @@ asmlinkage long sys_semtimedop(int semid, struct sembuf __user *tsops,
*/
if (timeout && jiffies_left == 0)
error = -EAGAIN;
remove_from_queue(sma,&queue);
list_del(&queue.list);
goto out_unlock_free;

out_unlock_free:
Expand Down

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