Commit 1a233956 authored by Manfred Spraul's avatar Manfred Spraul Committed by Linus Torvalds
Browse files

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

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: default avatarManfred Spraul <manfred@colorfullife.com>
Acked-by: default avatarKees 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e41d5818

include/linux/sem.h

+21 −1
Original line number Diff line number Diff line
@@ -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

ipc/sem.c

+34 −54
Original line number Diff line number Diff line
@@ -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 @@ undo: 
	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 @@ again: 
		 * 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 @@ again: 
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];

				/*

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