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ipc/sem.c: remove sem_base, embed struct sem
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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

[manfred@colorfullife.com: s/[0]/[]/, per hch]
  Link: http://lkml.kernel.org/r/20170525185107.12869-2-manfred@colorfullife.com
Link: http://lkml.kernel.org/r/20170515171912.6298-2-manfred@colorfullife.com
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: <1vier1@web.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Fabian Frederick <fabf@skynet.be>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Manfred Spraul authored and Linus Torvalds committed Jul 12, 2017
1 parent e41d581 commit 1a23395
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Showing 2 changed files with 55 additions and 55 deletions.
22 changes: 21 additions & 1 deletion include/linux/sem.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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 */
Expand All @@ -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
Expand Down
88 changes: 34 additions & 54 deletions ipc/sem.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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 {
Expand Down Expand Up @@ -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:
Expand Down Expand Up @@ -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);
}
Expand All @@ -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);
}
Expand Down Expand Up @@ -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);
}
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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);
}
}
Expand Down Expand Up @@ -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;
Expand All @@ -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;
Expand Down Expand Up @@ -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;

Expand All @@ -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--;
}

Expand All @@ -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--;
Expand Down Expand Up @@ -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;

Expand All @@ -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;

Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);
}
Expand All @@ -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);
}
Expand Down Expand Up @@ -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) {
Expand All @@ -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);
Expand Down Expand Up @@ -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();
}
}
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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)
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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);
Expand All @@ -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:
Expand Down Expand Up @@ -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) {
Expand Down Expand Up @@ -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];
/*
Expand Down

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