[PATCH 01/20] ipc/sem.c: remove sem_base, embed struct sem
From: Manfred Spraul
Date: Thu May 25 2017 - 14:56:18 EST
sma->sem_base is initialized with
sma->sem_base = (struct sem *) &sma[1];
The current code has four problems:
- There is an unnecessary pointer dereference - sem_base is not needed.
- Alignment for struct sem only works by chance.
- The current code causes false positive for static code analysis.
- This is a cast between different non-void types, which the future
randstruct GCC plugin warns on.
And, as bonus, the code size gets smaller:
Before:
0 .text 00003770
After:
0 .text 0000374e
Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
---
include/linux/sem.h | 22 +++++++++++++-
ipc/sem.c | 88 +++++++++++++++++++++--------------------------------
2 files changed, 55 insertions(+), 55 deletions(-)
diff --git a/include/linux/sem.h b/include/linux/sem.h
index 9edec92..9db1409 100644
--- a/include/linux/sem.h
+++ b/include/linux/sem.h
@@ -8,11 +8,29 @@
struct task_struct;
+/* One semaphore structure for each semaphore in the system. */
+struct sem {
+ int semval; /* current value */
+ /*
+ * PID of the process that last modified the semaphore. For
+ * Linux, specifically these are:
+ * - semop
+ * - semctl, via SETVAL and SETALL.
+ * - at task exit when performing undo adjustments (see exit_sem).
+ */
+ int sempid;
+ spinlock_t lock; /* spinlock for fine-grained semtimedop */
+ struct list_head pending_alter; /* pending single-sop operations */
+ /* that alter the semaphore */
+ struct list_head pending_const; /* pending single-sop operations */
+ /* that do not alter the semaphore*/
+ time_t sem_otime; /* candidate for sem_otime */
+} ____cacheline_aligned_in_smp;
+
/* One sem_array data structure for each set of semaphores in the system. */
struct sem_array {
struct kern_ipc_perm sem_perm; /* permissions .. see ipc.h */
time_t sem_ctime; /* last change time */
- struct sem *sem_base; /* ptr to first semaphore in array */
struct list_head pending_alter; /* pending operations */
/* that alter the array */
struct list_head pending_const; /* pending complex operations */
@@ -21,6 +39,8 @@ struct sem_array {
int sem_nsems; /* no. of semaphores in array */
int complex_count; /* pending complex operations */
unsigned int use_global_lock;/* >0: global lock required */
+
+ struct sem sems[];
};
#ifdef CONFIG_SYSVIPC
diff --git a/ipc/sem.c b/ipc/sem.c
index 947dc23..fff8337 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -87,24 +87,6 @@
#include <linux/uaccess.h>
#include "util.h"
-/* One semaphore structure for each semaphore in the system. */
-struct sem {
- int semval; /* current value */
- /*
- * PID of the process that last modified the semaphore. For
- * Linux, specifically these are:
- * - semop
- * - semctl, via SETVAL and SETALL.
- * - at task exit when performing undo adjustments (see exit_sem).
- */
- int sempid;
- spinlock_t lock; /* spinlock for fine-grained semtimedop */
- struct list_head pending_alter; /* pending single-sop operations */
- /* that alter the semaphore */
- struct list_head pending_const; /* pending single-sop operations */
- /* that do not alter the semaphore*/
- time_t sem_otime; /* candidate for sem_otime */
-} ____cacheline_aligned_in_smp;
/* One queue for each sleeping process in the system. */
struct sem_queue {
@@ -175,7 +157,7 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it);
* sem_array.sem_undo
*
* b) global or semaphore sem_lock() for read/write:
- * sem_array.sem_base[i].pending_{const,alter}:
+ * sem_array.sems[i].pending_{const,alter}:
*
* c) special:
* sem_undo_list.list_proc:
@@ -250,7 +232,7 @@ static void unmerge_queues(struct sem_array *sma)
*/
list_for_each_entry_safe(q, tq, &sma->pending_alter, list) {
struct sem *curr;
- curr = &sma->sem_base[q->sops[0].sem_num];
+ curr = &sma->sems[q->sops[0].sem_num];
list_add_tail(&q->list, &curr->pending_alter);
}
@@ -270,7 +252,7 @@ static void merge_queues(struct sem_array *sma)
{
int i;
for (i = 0; i < sma->sem_nsems; i++) {
- struct sem *sem = sma->sem_base + i;
+ struct sem *sem = &sma->sems[i];
list_splice_init(&sem->pending_alter, &sma->pending_alter);
}
@@ -306,7 +288,7 @@ static void complexmode_enter(struct sem_array *sma)
sma->use_global_lock = USE_GLOBAL_LOCK_HYSTERESIS;
for (i = 0; i < sma->sem_nsems; i++) {
- sem = sma->sem_base + i;
+ sem = &sma->sems[i];
spin_lock(&sem->lock);
spin_unlock(&sem->lock);
}
@@ -366,7 +348,7 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
*
* Both facts are tracked by use_global_mode.
*/
- sem = sma->sem_base + sops->sem_num;
+ sem = &sma->sems[sops->sem_num];
/*
* Initial check for use_global_lock. Just an optimization,
@@ -421,7 +403,7 @@ static inline void sem_unlock(struct sem_array *sma, int locknum)
complexmode_tryleave(sma);
ipc_unlock_object(&sma->sem_perm);
} else {
- struct sem *sem = sma->sem_base + locknum;
+ struct sem *sem = &sma->sems[locknum];
spin_unlock(&sem->lock);
}
}
@@ -487,7 +469,7 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
if (ns->used_sems + nsems > ns->sc_semmns)
return -ENOSPC;
- size = sizeof(*sma) + nsems * sizeof(struct sem);
+ size = sizeof(*sma) + nsems * sizeof(sma->sems[0]);
sma = ipc_rcu_alloc(size);
if (!sma)
return -ENOMEM;
@@ -504,12 +486,10 @@ static int newary(struct ipc_namespace *ns, struct ipc_params *params)
return retval;
}
- sma->sem_base = (struct sem *) &sma[1];
-
for (i = 0; i < nsems; i++) {
- INIT_LIST_HEAD(&sma->sem_base[i].pending_alter);
- INIT_LIST_HEAD(&sma->sem_base[i].pending_const);
- spin_lock_init(&sma->sem_base[i].lock);
+ INIT_LIST_HEAD(&sma->sems[i].pending_alter);
+ INIT_LIST_HEAD(&sma->sems[i].pending_const);
+ spin_lock_init(&sma->sems[i].lock);
}
sma->complex_count = 0;
@@ -612,7 +592,7 @@ static int perform_atomic_semop_slow(struct sem_array *sma, struct sem_queue *q)
un = q->undo;
for (sop = sops; sop < sops + nsops; sop++) {
- curr = sma->sem_base + sop->sem_num;
+ curr = &sma->sems[sop->sem_num];
sem_op = sop->sem_op;
result = curr->semval;
@@ -639,7 +619,7 @@ static int perform_atomic_semop_slow(struct sem_array *sma, struct sem_queue *q)
sop--;
pid = q->pid;
while (sop >= sops) {
- sma->sem_base[sop->sem_num].sempid = pid;
+ sma->sems[sop->sem_num].sempid = pid;
sop--;
}
@@ -661,7 +641,7 @@ static int perform_atomic_semop_slow(struct sem_array *sma, struct sem_queue *q)
sop--;
while (sop >= sops) {
sem_op = sop->sem_op;
- sma->sem_base[sop->sem_num].semval -= sem_op;
+ sma->sems[sop->sem_num].semval -= sem_op;
if (sop->sem_flg & SEM_UNDO)
un->semadj[sop->sem_num] += sem_op;
sop--;
@@ -692,7 +672,7 @@ static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
* until the operations can go through.
*/
for (sop = sops; sop < sops + nsops; sop++) {
- curr = sma->sem_base + sop->sem_num;
+ curr = &sma->sems[sop->sem_num];
sem_op = sop->sem_op;
result = curr->semval;
@@ -716,7 +696,7 @@ static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
}
for (sop = sops; sop < sops + nsops; sop++) {
- curr = sma->sem_base + sop->sem_num;
+ curr = &sma->sems[sop->sem_num];
sem_op = sop->sem_op;
result = curr->semval;
@@ -815,7 +795,7 @@ static int wake_const_ops(struct sem_array *sma, int semnum,
if (semnum == -1)
pending_list = &sma->pending_const;
else
- pending_list = &sma->sem_base[semnum].pending_const;
+ pending_list = &sma->sems[semnum].pending_const;
list_for_each_entry_safe(q, tmp, pending_list, list) {
int error = perform_atomic_semop(sma, q);
@@ -856,7 +836,7 @@ static int do_smart_wakeup_zero(struct sem_array *sma, struct sembuf *sops,
for (i = 0; i < nsops; i++) {
int num = sops[i].sem_num;
- if (sma->sem_base[num].semval == 0) {
+ if (sma->sems[num].semval == 0) {
got_zero = 1;
semop_completed |= wake_const_ops(sma, num, wake_q);
}
@@ -867,7 +847,7 @@ static int do_smart_wakeup_zero(struct sem_array *sma, struct sembuf *sops,
* Assume all were changed.
*/
for (i = 0; i < sma->sem_nsems; i++) {
- if (sma->sem_base[i].semval == 0) {
+ if (sma->sems[i].semval == 0) {
got_zero = 1;
semop_completed |= wake_const_ops(sma, i, wake_q);
}
@@ -909,7 +889,7 @@ static int update_queue(struct sem_array *sma, int semnum, struct wake_q_head *w
if (semnum == -1)
pending_list = &sma->pending_alter;
else
- pending_list = &sma->sem_base[semnum].pending_alter;
+ pending_list = &sma->sems[semnum].pending_alter;
again:
list_for_each_entry_safe(q, tmp, pending_list, list) {
@@ -922,7 +902,7 @@ static int update_queue(struct sem_array *sma, int semnum, struct wake_q_head *w
* be in the per semaphore pending queue, and decrements
* cannot be successful if the value is already 0.
*/
- if (semnum != -1 && sma->sem_base[semnum].semval == 0)
+ if (semnum != -1 && sma->sems[semnum].semval == 0)
break;
error = perform_atomic_semop(sma, q);
@@ -959,9 +939,9 @@ static int update_queue(struct sem_array *sma, int semnum, struct wake_q_head *w
static void set_semotime(struct sem_array *sma, struct sembuf *sops)
{
if (sops == NULL) {
- sma->sem_base[0].sem_otime = get_seconds();
+ sma->sems[0].sem_otime = get_seconds();
} else {
- sma->sem_base[sops[0].sem_num].sem_otime =
+ sma->sems[sops[0].sem_num].sem_otime =
get_seconds();
}
}
@@ -1067,9 +1047,9 @@ static int count_semcnt(struct sem_array *sma, ushort semnum,
semcnt = 0;
/* First: check the simple operations. They are easy to evaluate */
if (count_zero)
- l = &sma->sem_base[semnum].pending_const;
+ l = &sma->sems[semnum].pending_const;
else
- l = &sma->sem_base[semnum].pending_alter;
+ l = &sma->sems[semnum].pending_alter;
list_for_each_entry(q, l, list) {
/* all task on a per-semaphore list sleep on exactly
@@ -1124,7 +1104,7 @@ static void freeary(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp)
wake_up_sem_queue_prepare(q, -EIDRM, &wake_q);
}
for (i = 0; i < sma->sem_nsems; i++) {
- struct sem *sem = sma->sem_base + i;
+ struct sem *sem = &sma->sems[i];
list_for_each_entry_safe(q, tq, &sem->pending_const, list) {
unlink_queue(sma, q);
wake_up_sem_queue_prepare(q, -EIDRM, &wake_q);
@@ -1174,9 +1154,9 @@ static time_t get_semotime(struct sem_array *sma)
int i;
time_t res;
- res = sma->sem_base[0].sem_otime;
+ res = sma->sems[0].sem_otime;
for (i = 1; i < sma->sem_nsems; i++) {
- time_t to = sma->sem_base[i].sem_otime;
+ time_t to = sma->sems[i].sem_otime;
if (to > res)
res = to;
@@ -1325,7 +1305,7 @@ static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum,
return -EIDRM;
}
- curr = &sma->sem_base[semnum];
+ curr = &sma->sems[semnum];
ipc_assert_locked_object(&sma->sem_perm);
list_for_each_entry(un, &sma->list_id, list_id)
@@ -1402,7 +1382,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
}
}
for (i = 0; i < sma->sem_nsems; i++)
- sem_io[i] = sma->sem_base[i].semval;
+ sem_io[i] = sma->sems[i].semval;
sem_unlock(sma, -1);
rcu_read_unlock();
err = 0;
@@ -1450,8 +1430,8 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
}
for (i = 0; i < nsems; i++) {
- sma->sem_base[i].semval = sem_io[i];
- sma->sem_base[i].sempid = task_tgid_vnr(current);
+ sma->sems[i].semval = sem_io[i];
+ sma->sems[i].sempid = task_tgid_vnr(current);
}
ipc_assert_locked_object(&sma->sem_perm);
@@ -1476,7 +1456,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
err = -EIDRM;
goto out_unlock;
}
- curr = &sma->sem_base[semnum];
+ curr = &sma->sems[semnum];
switch (cmd) {
case GETVAL:
@@ -1932,7 +1912,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
*/
if (nsops == 1) {
struct sem *curr;
- curr = &sma->sem_base[sops->sem_num];
+ curr = &sma->sems[sops->sem_num];
if (alter) {
if (sma->complex_count) {
@@ -2146,7 +2126,7 @@ void exit_sem(struct task_struct *tsk)
/* perform adjustments registered in un */
for (i = 0; i < sma->sem_nsems; i++) {
- struct sem *semaphore = &sma->sem_base[i];
+ struct sem *semaphore = &sma->sems[i];
if (un->semadj[i]) {
semaphore->semval += un->semadj[i];
/*
--
2.9.3