From: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Subject: 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@xxxxxxxxxxxxxxxx: s/[0]/[]/, per hch] Link: http://lkml.kernel.org/r/20170525185107.12869-2-manfred@xxxxxxxxxxxxxxxx Link: http://lkml.kernel.org/r/20170515171912.6298-2-manfred@xxxxxxxxxxxxxxxx Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: <1vier1@xxxxxx> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Fabian Frederick <fabf@xxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/sem.h | 22 ++++++++++ ipc/sem.c | 88 ++++++++++++++++-------------------------- 2 files changed, 55 insertions(+), 55 deletions(-) diff -puN include/linux/sem.h~ipc-semc-remove-sem_base-embed-struct-sem include/linux/sem.h --- a/include/linux/sem.h~ipc-semc-remove-sem_base-embed-struct-sem +++ a/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 -puN ipc/sem.c~ipc-semc-remove-sem_base-embed-struct-sem ipc/sem.c --- a/ipc/sem.c~ipc-semc-remove-sem_base-embed-struct-sem +++ a/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 * 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_ar */ 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_arra { 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 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_ar * * 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 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 * 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 * 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(str 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(str 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 s * 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 s } 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_arr 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 s 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 s * 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 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 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 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_ar 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_name 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_namesp } } 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_namesp } 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_namesp 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, */ 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]; /* _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
