2 * linux/arch/i386/kernel/process.c
4 * Copyright (C) 1995 Linus Torvalds
6 * Pentium III FXSR, SSE support
7 * Gareth Hughes <gareth@valinux.com>, May 2000
11 * This file handles the architecture-dependent parts of process handling..
16 #include <linux/cpu.h>
17 #include <linux/errno.h>
18 #include <linux/sched.h>
20 #include <linux/kernel.h>
22 #include <linux/elfcore.h>
23 #include <linux/smp.h>
24 #include <linux/smp_lock.h>
25 #include <linux/stddef.h>
26 #include <linux/slab.h>
27 #include <linux/vmalloc.h>
28 #include <linux/user.h>
29 #include <linux/a.out.h>
30 #include <linux/interrupt.h>
31 #include <linux/config.h>
32 #include <linux/utsname.h>
33 #include <linux/delay.h>
34 #include <linux/reboot.h>
35 #include <linux/init.h>
36 #include <linux/mc146818rtc.h>
37 #include <linux/module.h>
38 #include <linux/kallsyms.h>
39 #include <linux/ptrace.h>
40 #include <linux/random.h>
42 #include <asm/uaccess.h>
43 #include <asm/pgtable.h>
44 #include <asm/system.h>
47 #include <asm/processor.h>
51 #ifdef CONFIG_MATH_EMULATION
52 #include <asm/math_emu.h>
55 #include <xen/interface/physdev.h>
56 #include <xen/interface/vcpu.h>
57 #include <xen/cpu_hotplug.h>
59 #include <linux/err.h>
61 #include <asm/tlbflush.h>
64 #include <asm/tlbflush.h>
67 asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
69 static int hlt_counter;
71 unsigned long boot_option_idle_override = 0;
72 EXPORT_SYMBOL(boot_option_idle_override);
75 * Return saved PC of a blocked thread.
77 unsigned long thread_saved_pc(struct task_struct *tsk)
79 return ((unsigned long *)tsk->thread.esp)[3];
83 * Powermanagement idle function, if any..
85 void (*pm_idle)(void);
86 EXPORT_SYMBOL(pm_idle);
87 static DEFINE_PER_CPU(unsigned int, cpu_idle_state);
89 void disable_hlt(void)
94 EXPORT_SYMBOL(disable_hlt);
101 EXPORT_SYMBOL(enable_hlt);
103 /* XXX XEN doesn't use default_idle(), poll_idle(). Use xen_idle() instead. */
111 clear_thread_flag(TIF_POLLING_NRFLAG);
112 smp_mb__after_clear_bit();
114 set_thread_flag(TIF_POLLING_NRFLAG);
117 #ifdef CONFIG_APM_MODULE
118 EXPORT_SYMBOL(default_idle);
121 #ifdef CONFIG_HOTPLUG_CPU
122 extern cpumask_t cpu_initialized;
123 static inline void play_dead(void)
127 cpu_clear(smp_processor_id(), cpu_initialized);
128 preempt_enable_no_resched();
129 HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
133 static inline void play_dead(void)
137 #endif /* CONFIG_HOTPLUG_CPU */
140 * The idle thread. There's no useful work to be
141 * done, so just try to conserve power and have a
142 * low exit latency (ie sit in a loop waiting for
143 * somebody to say that they'd like to reschedule)
147 int cpu = smp_processor_id();
149 set_thread_flag(TIF_POLLING_NRFLAG);
151 /* endless idle loop with no priority at all */
153 while (!need_resched()) {
155 if (__get_cpu_var(cpu_idle_state))
156 __get_cpu_var(cpu_idle_state) = 0;
160 if (cpu_is_offline(cpu))
163 __get_cpu_var(irq_stat).idle_timestamp = jiffies;
166 preempt_enable_no_resched();
172 void cpu_idle_wait(void)
174 unsigned int cpu, this_cpu = get_cpu();
177 set_cpus_allowed(current, cpumask_of_cpu(this_cpu));
181 for_each_online_cpu(cpu) {
182 per_cpu(cpu_idle_state, cpu) = 1;
186 __get_cpu_var(cpu_idle_state) = 0;
191 for_each_online_cpu(cpu) {
192 if (cpu_isset(cpu, map) && !per_cpu(cpu_idle_state, cpu))
195 cpus_and(map, map, cpu_online_map);
196 } while (!cpus_empty(map));
198 EXPORT_SYMBOL_GPL(cpu_idle_wait);
200 /* XXX XEN doesn't use mwait_idle(), select_idle_routine(), idle_setup(). */
201 /* Always use xen_idle() instead. */
202 void __devinit select_idle_routine(const struct cpuinfo_x86 *c) {}
204 void show_regs(struct pt_regs * regs)
206 unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
209 printk("Pid: %d, comm: %20s\n", current->pid, current->comm);
210 printk("EIP: %04x:[<%08lx>] CPU: %d\n",0xffff & regs->xcs,regs->eip, smp_processor_id());
211 print_symbol("EIP is at %s\n", regs->eip);
213 if (user_mode_vm(regs))
214 printk(" ESP: %04x:%08lx",0xffff & regs->xss,regs->esp);
215 printk(" EFLAGS: %08lx %s (%s %.*s)\n",
216 regs->eflags, print_tainted(), system_utsname.release,
217 (int)strcspn(system_utsname.version, " "),
218 system_utsname.version);
219 printk("EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
220 regs->eax,regs->ebx,regs->ecx,regs->edx);
221 printk("ESI: %08lx EDI: %08lx EBP: %08lx",
222 regs->esi, regs->edi, regs->ebp);
223 printk(" DS: %04x ES: %04x\n",
224 0xffff & regs->xds,0xffff & regs->xes);
229 cr4 = read_cr4_safe();
230 printk("CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n", cr0, cr2, cr3, cr4);
231 show_trace(NULL, ®s->esp);
235 * This gets run with %ebx containing the
236 * function to call, and %edx containing
239 extern void kernel_thread_helper(void);
240 __asm__(".section .text\n"
242 "kernel_thread_helper:\n\t"
251 * Create a kernel thread
253 int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
257 memset(®s, 0, sizeof(regs));
259 regs.ebx = (unsigned long) fn;
260 regs.edx = (unsigned long) arg;
262 regs.xds = __USER_DS;
263 regs.xes = __USER_DS;
265 regs.eip = (unsigned long) kernel_thread_helper;
266 regs.xcs = GET_KERNEL_CS();
267 regs.eflags = X86_EFLAGS_IF | X86_EFLAGS_SF | X86_EFLAGS_PF | 0x2;
269 /* Ok, create the new process.. */
270 return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, ®s, 0, NULL, NULL);
272 EXPORT_SYMBOL(kernel_thread);
275 * Free current thread data structures etc..
277 void exit_thread(void)
279 struct task_struct *tsk = current;
280 struct thread_struct *t = &tsk->thread;
282 /* The process may have allocated an io port bitmap... nuke it. */
283 if (unlikely(NULL != t->io_bitmap_ptr)) {
284 struct physdev_set_iobitmap set_iobitmap = { 0 };
285 HYPERVISOR_physdev_op(PHYSDEVOP_set_iobitmap, &set_iobitmap);
286 kfree(t->io_bitmap_ptr);
287 t->io_bitmap_ptr = NULL;
291 void flush_thread(void)
293 struct task_struct *tsk = current;
295 memset(tsk->thread.debugreg, 0, sizeof(unsigned long)*8);
296 memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
298 * Forget coprocessor state..
304 void release_thread(struct task_struct *dead_task)
306 BUG_ON(dead_task->mm);
307 release_vm86_irqs(dead_task);
311 * This gets called before we allocate a new thread and copy
312 * the current task into it.
314 void prepare_to_copy(struct task_struct *tsk)
319 int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
320 unsigned long unused,
321 struct task_struct * p, struct pt_regs * regs)
323 struct pt_regs * childregs;
324 struct task_struct *tsk;
327 childregs = task_pt_regs(p);
330 childregs->esp = esp;
332 p->thread.esp = (unsigned long) childregs;
333 p->thread.esp0 = (unsigned long) (childregs+1);
335 p->thread.eip = (unsigned long) ret_from_fork;
337 savesegment(fs,p->thread.fs);
338 savesegment(gs,p->thread.gs);
341 if (unlikely(NULL != tsk->thread.io_bitmap_ptr)) {
342 p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
343 if (!p->thread.io_bitmap_ptr) {
344 p->thread.io_bitmap_max = 0;
347 memcpy(p->thread.io_bitmap_ptr, tsk->thread.io_bitmap_ptr,
352 * Set a new TLS for the child thread?
354 if (clone_flags & CLONE_SETTLS) {
355 struct desc_struct *desc;
356 struct user_desc info;
360 if (copy_from_user(&info, (void __user *)childregs->esi, sizeof(info)))
363 if (LDT_empty(&info))
366 idx = info.entry_number;
367 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
370 desc = p->thread.tls_array + idx - GDT_ENTRY_TLS_MIN;
371 desc->a = LDT_entry_a(&info);
372 desc->b = LDT_entry_b(&info);
375 p->thread.iopl = current->thread.iopl;
379 if (err && p->thread.io_bitmap_ptr) {
380 kfree(p->thread.io_bitmap_ptr);
381 p->thread.io_bitmap_max = 0;
387 * fill in the user structure for a core dump..
389 void dump_thread(struct pt_regs * regs, struct user * dump)
393 /* changed the size calculations - should hopefully work better. lbt */
394 dump->magic = CMAGIC;
395 dump->start_code = 0;
396 dump->start_stack = regs->esp & ~(PAGE_SIZE - 1);
397 dump->u_tsize = ((unsigned long) current->mm->end_code) >> PAGE_SHIFT;
398 dump->u_dsize = ((unsigned long) (current->mm->brk + (PAGE_SIZE-1))) >> PAGE_SHIFT;
399 dump->u_dsize -= dump->u_tsize;
401 for (i = 0; i < 8; i++)
402 dump->u_debugreg[i] = current->thread.debugreg[i];
404 if (dump->start_stack < TASK_SIZE)
405 dump->u_ssize = ((unsigned long) (TASK_SIZE - dump->start_stack)) >> PAGE_SHIFT;
407 dump->regs.ebx = regs->ebx;
408 dump->regs.ecx = regs->ecx;
409 dump->regs.edx = regs->edx;
410 dump->regs.esi = regs->esi;
411 dump->regs.edi = regs->edi;
412 dump->regs.ebp = regs->ebp;
413 dump->regs.eax = regs->eax;
414 dump->regs.ds = regs->xds;
415 dump->regs.es = regs->xes;
416 savesegment(fs,dump->regs.fs);
417 savesegment(gs,dump->regs.gs);
418 dump->regs.orig_eax = regs->orig_eax;
419 dump->regs.eip = regs->eip;
420 dump->regs.cs = regs->xcs;
421 dump->regs.eflags = regs->eflags;
422 dump->regs.esp = regs->esp;
423 dump->regs.ss = regs->xss;
425 dump->u_fpvalid = dump_fpu (regs, &dump->i387);
427 EXPORT_SYMBOL(dump_thread);
430 * Capture the user space registers if the task is not running (in user space)
432 int dump_task_regs(struct task_struct *tsk, elf_gregset_t *regs)
434 struct pt_regs ptregs = *task_pt_regs(tsk);
435 ptregs.xcs &= 0xffff;
436 ptregs.xds &= 0xffff;
437 ptregs.xes &= 0xffff;
438 ptregs.xss &= 0xffff;
440 elf_core_copy_regs(regs, &ptregs);
446 * This function selects if the context switch from prev to next
447 * has to tweak the TSC disable bit in the cr4.
449 static inline void disable_tsc(struct task_struct *prev_p,
450 struct task_struct *next_p)
452 struct thread_info *prev, *next;
455 * gcc should eliminate the ->thread_info dereference if
456 * has_secure_computing returns 0 at compile time (SECCOMP=n).
458 prev = task_thread_info(prev_p);
459 next = task_thread_info(next_p);
461 if (has_secure_computing(prev) || has_secure_computing(next)) {
463 if (has_secure_computing(prev) &&
464 !has_secure_computing(next)) {
465 write_cr4(read_cr4() & ~X86_CR4_TSD);
466 } else if (!has_secure_computing(prev) &&
467 has_secure_computing(next))
468 write_cr4(read_cr4() | X86_CR4_TSD);
473 * switch_to(x,yn) should switch tasks from x to y.
475 * We fsave/fwait so that an exception goes off at the right time
476 * (as a call from the fsave or fwait in effect) rather than to
477 * the wrong process. Lazy FP saving no longer makes any sense
478 * with modern CPU's, and this simplifies a lot of things (SMP
479 * and UP become the same).
481 * NOTE! We used to use the x86 hardware context switching. The
482 * reason for not using it any more becomes apparent when you
483 * try to recover gracefully from saved state that is no longer
484 * valid (stale segment register values in particular). With the
485 * hardware task-switch, there is no way to fix up bad state in
486 * a reasonable manner.
488 * The fact that Intel documents the hardware task-switching to
489 * be slow is a fairly red herring - this code is not noticeably
490 * faster. However, there _is_ some room for improvement here,
491 * so the performance issues may eventually be a valid point.
492 * More important, however, is the fact that this allows us much
495 * The return value (in %eax) will be the "prev" task after
496 * the task-switch, and shows up in ret_from_fork in entry.S,
499 struct task_struct fastcall * __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
501 struct thread_struct *prev = &prev_p->thread,
502 *next = &next_p->thread;
503 int cpu = smp_processor_id();
504 #ifndef CONFIG_X86_NO_TSS
505 struct tss_struct *tss = &per_cpu(init_tss, cpu);
507 struct physdev_set_iopl iopl_op;
508 struct physdev_set_iobitmap iobmp_op;
509 multicall_entry_t _mcl[8], *mcl = _mcl;
511 /* XEN NOTE: FS/GS saved in switch_mm(), not here. */
514 * This is basically '__unlazy_fpu', except that we queue a
515 * multicall to indicate FPU task switch, rather than
516 * synchronously trapping to Xen.
518 if (prev_p->thread_info->status & TS_USEDFPU) {
519 __save_init_fpu(prev_p); /* _not_ save_init_fpu() */
520 mcl->op = __HYPERVISOR_fpu_taskswitch;
524 #if 0 /* lazy fpu sanity check */
525 else BUG_ON(!(read_cr0() & 8));
528 load_user_cs_desc(cpu, next_p->mm);
532 * This is load_esp0(tss, next) with a multicall.
534 mcl->op = __HYPERVISOR_stack_switch;
535 mcl->args[0] = __KERNEL_DS;
536 mcl->args[1] = next->esp0;
540 * Load the per-thread Thread-Local Storage descriptor.
541 * This is load_TLS(next, cpu) with multicalls.
544 if (unlikely(next->tls_array[i].a != prev->tls_array[i].a || \
545 next->tls_array[i].b != prev->tls_array[i].b)) { \
546 mcl->op = __HYPERVISOR_update_descriptor; \
547 *(u64 *)&mcl->args[0] = virt_to_machine( \
548 &get_cpu_gdt_table(cpu)[GDT_ENTRY_TLS_MIN + i]);\
549 *(u64 *)&mcl->args[2] = *(u64 *)&next->tls_array[i]; \
556 if (unlikely(prev->iopl != next->iopl)) {
557 iopl_op.iopl = (next->iopl == 0) ? 1 : (next->iopl >> 12) & 3;
558 mcl->op = __HYPERVISOR_physdev_op;
559 mcl->args[0] = PHYSDEVOP_set_iopl;
560 mcl->args[1] = (unsigned long)&iopl_op;
564 if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr)) {
565 iobmp_op.bitmap = (char *)next->io_bitmap_ptr;
566 iobmp_op.nr_ports = next->io_bitmap_ptr ? IO_BITMAP_BITS : 0;
567 mcl->op = __HYPERVISOR_physdev_op;
568 mcl->args[0] = PHYSDEVOP_set_iobitmap;
569 mcl->args[1] = (unsigned long)&iobmp_op;
573 (void)HYPERVISOR_multicall(_mcl, mcl - _mcl);
576 * Restore %fs and %gs if needed.
578 * Glibc normally makes %fs be zero, and %gs is one of
581 if (unlikely(next->fs))
582 loadsegment(fs, next->fs);
585 loadsegment(gs, next->gs);
588 * Now maybe reload the debug registers
590 if (unlikely(next->debugreg[7])) {
591 set_debugreg(next->debugreg[0], 0);
592 set_debugreg(next->debugreg[1], 1);
593 set_debugreg(next->debugreg[2], 2);
594 set_debugreg(next->debugreg[3], 3);
596 set_debugreg(next->debugreg[6], 6);
597 set_debugreg(next->debugreg[7], 7);
600 disable_tsc(prev_p, next_p);
605 asmlinkage int sys_fork(struct pt_regs regs)
607 return do_fork(SIGCHLD, regs.esp, ®s, 0, NULL, NULL);
610 asmlinkage int sys_clone(struct pt_regs regs)
612 unsigned long clone_flags;
614 int __user *parent_tidptr, *child_tidptr;
616 clone_flags = regs.ebx;
618 parent_tidptr = (int __user *)regs.edx;
619 child_tidptr = (int __user *)regs.edi;
622 return do_fork(clone_flags, newsp, ®s, 0, parent_tidptr, child_tidptr);
626 * This is trivial, and on the face of it looks like it
627 * could equally well be done in user mode.
629 * Not so, for quite unobvious reasons - register pressure.
630 * In user mode vfork() cannot have a stack frame, and if
631 * done by calling the "clone()" system call directly, you
632 * do not have enough call-clobbered registers to hold all
633 * the information you need.
635 asmlinkage int sys_vfork(struct pt_regs regs)
637 return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, regs.esp, ®s, 0, NULL, NULL);
641 * sys_execve() executes a new program.
643 asmlinkage int sys_execve(struct pt_regs regs)
648 filename = getname((char __user *) regs.ebx);
649 error = PTR_ERR(filename);
650 if (IS_ERR(filename))
652 error = do_execve(filename,
653 (char __user * __user *) regs.ecx,
654 (char __user * __user *) regs.edx,
658 current->ptrace &= ~PT_DTRACE;
659 task_unlock(current);
660 /* Make sure we don't return using sysenter.. */
661 set_thread_flag(TIF_IRET);
668 #define top_esp (THREAD_SIZE - sizeof(unsigned long))
669 #define top_ebp (THREAD_SIZE - 2*sizeof(unsigned long))
671 unsigned long get_wchan(struct task_struct *p)
673 unsigned long ebp, esp, eip;
674 unsigned long stack_page;
676 if (!p || p == current || p->state == TASK_RUNNING)
678 stack_page = (unsigned long)task_stack_page(p);
680 if (!stack_page || esp < stack_page || esp > top_esp+stack_page)
682 /* include/asm-i386/system.h:switch_to() pushes ebp last. */
683 ebp = *(unsigned long *) esp;
685 if (ebp < stack_page || ebp > top_ebp+stack_page)
687 eip = *(unsigned long *) (ebp+4);
688 if (!in_sched_functions(eip))
690 ebp = *(unsigned long *) ebp;
691 } while (count++ < 16);
696 * sys_alloc_thread_area: get a yet unused TLS descriptor index.
698 static int get_free_idx(void)
700 struct thread_struct *t = ¤t->thread;
703 for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
704 if (desc_empty(t->tls_array + idx))
705 return idx + GDT_ENTRY_TLS_MIN;
710 * Set a given TLS descriptor:
712 asmlinkage int sys_set_thread_area(struct user_desc __user *u_info)
714 struct thread_struct *t = ¤t->thread;
715 struct user_desc info;
716 struct desc_struct *desc;
719 if (copy_from_user(&info, u_info, sizeof(info)))
721 idx = info.entry_number;
724 * index -1 means the kernel should try to find and
725 * allocate an empty descriptor:
728 idx = get_free_idx();
731 if (put_user(idx, &u_info->entry_number))
735 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
738 desc = t->tls_array + idx - GDT_ENTRY_TLS_MIN;
741 * We must not get preempted while modifying the TLS.
745 if (LDT_empty(&info)) {
749 desc->a = LDT_entry_a(&info);
750 desc->b = LDT_entry_b(&info);
760 * Get the current Thread-Local Storage area:
763 #define GET_BASE(desc) ( \
764 (((desc)->a >> 16) & 0x0000ffff) | \
765 (((desc)->b << 16) & 0x00ff0000) | \
766 ( (desc)->b & 0xff000000) )
768 #define GET_LIMIT(desc) ( \
769 ((desc)->a & 0x0ffff) | \
770 ((desc)->b & 0xf0000) )
772 #define GET_32BIT(desc) (((desc)->b >> 22) & 1)
773 #define GET_CONTENTS(desc) (((desc)->b >> 10) & 3)
774 #define GET_WRITABLE(desc) (((desc)->b >> 9) & 1)
775 #define GET_LIMIT_PAGES(desc) (((desc)->b >> 23) & 1)
776 #define GET_PRESENT(desc) (((desc)->b >> 15) & 1)
777 #define GET_USEABLE(desc) (((desc)->b >> 20) & 1)
779 asmlinkage int sys_get_thread_area(struct user_desc __user *u_info)
781 struct user_desc info;
782 struct desc_struct *desc;
785 if (get_user(idx, &u_info->entry_number))
787 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
790 memset(&info, 0, sizeof(info));
792 desc = current->thread.tls_array + idx - GDT_ENTRY_TLS_MIN;
794 info.entry_number = idx;
795 info.base_addr = GET_BASE(desc);
796 info.limit = GET_LIMIT(desc);
797 info.seg_32bit = GET_32BIT(desc);
798 info.contents = GET_CONTENTS(desc);
799 info.read_exec_only = !GET_WRITABLE(desc);
800 info.limit_in_pages = GET_LIMIT_PAGES(desc);
801 info.seg_not_present = !GET_PRESENT(desc);
802 info.useable = GET_USEABLE(desc);
804 if (copy_to_user(u_info, &info, sizeof(info)))
809 unsigned long arch_align_stack(unsigned long sp)
811 if (randomize_va_space)
812 sp -= get_random_int() % 8192;
816 void arch_add_exec_range(struct mm_struct *mm, unsigned long limit)
818 if (limit > mm->context.exec_limit) {
819 mm->context.exec_limit = limit;
820 set_user_cs(&mm->context.user_cs, limit);
821 if (mm == current->mm) {
823 load_user_cs_desc(smp_processor_id(), mm);
828 void arch_remove_exec_range(struct mm_struct *mm, unsigned long old_end)
830 struct vm_area_struct *vma;
831 unsigned long limit = PAGE_SIZE;
833 if (old_end == mm->context.exec_limit) {
834 for (vma = mm->mmap; vma; vma = vma->vm_next)
835 if ((vma->vm_flags & VM_EXEC) && (vma->vm_end > limit))
838 mm->context.exec_limit = limit;
839 set_user_cs(&mm->context.user_cs, limit);
840 if (mm == current->mm) {
842 load_user_cs_desc(smp_processor_id(), mm);
848 void arch_flush_exec_range(struct mm_struct *mm)
850 mm->context.exec_limit = 0;
851 set_user_cs(&mm->context.user_cs, 0);
855 * Generate random brk address between 128MB and 196MB. (if the layout
858 void randomize_brk(unsigned long old_brk)
860 unsigned long new_brk, range_start, range_end;
862 range_start = 0x08000000;
863 if (current->mm->brk >= range_start)
864 range_start = current->mm->brk;
865 range_end = range_start + 0x02000000;
866 new_brk = randomize_range(range_start, range_end, 0);
868 current->mm->brk = new_brk;