arch/um/kernel/irq.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2017 - Cambridge Greys Ltd
   4  * Copyright (C) 2011 - 2014 Cisco Systems Inc
   5  * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   6  * Derived (i.e. mostly copied) from arch/i386/kernel/irq.c:
   7  *      Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
   8  */
   9
  10 #include <linux/cpumask.h>
  11 #include <linux/hardirq.h>
  12 #include <linux/interrupt.h>
  13 #include <linux/kernel_stat.h>
  14 #include <linux/module.h>
  15 #include <linux/sched.h>
  16 #include <linux/seq_file.h>
  17 #include <linux/slab.h>
  18 #include <as-layout.h>
  19 #include <kern_util.h>
  20 #include <os.h>
  21 #include <irq_user.h>
  22 #include <irq_kern.h>
  23 #include <linux/time-internal.h>
  24
  25
  26 extern void free_irqs(void);
  27
  28 /* When epoll triggers we do not know why it did so
  29  * we can also have different IRQs for read and write.
  30  * This is why we keep a small irq_reg array for each fd -
  31  * one entry per IRQ type
  32  */
  33 struct irq_reg {
  34         void *id;
  35         int irq;
  36         /* it's cheaper to store this than to query it */
  37         int events;
  38         bool active;
  39         bool pending;
  40         bool wakeup;
  41 #ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
  42         bool pending_on_resume;
  43         void (*timetravel_handler)(int, int, void *,
  44                                    struct time_travel_event *);
  45         struct time_travel_event event;
  46 #endif
  47 };
  48
  49 struct irq_entry {
  50         struct list_head list;
  51         int fd;
  52         struct irq_reg reg[NUM_IRQ_TYPES];
  53         bool suspended;
  54         bool sigio_workaround;
  55 };
  56
  57 static DEFINE_SPINLOCK(irq_lock);
  58 static LIST_HEAD(active_fds);
  59 static DECLARE_BITMAP(irqs_allocated, NR_IRQS);
  60 static bool irqs_suspended;
  61
  62 static void irq_io_loop(struct irq_reg *irq, struct uml_pt_regs *regs)
  63 {
  64 /*
  65  * irq->active guards against reentry
  66  * irq->pending accumulates pending requests
  67  * if pending is raised the irq_handler is re-run
  68  * until pending is cleared
  69  */
  70         if (irq->active) {
  71                 irq->active = false;
  72
  73                 do {
  74                         irq->pending = false;
  75                         do_IRQ(irq->irq, regs);
  76                 } while (irq->pending);
  77
  78                 irq->active = true;
  79         } else {
  80                 irq->pending = true;
  81         }
  82 }
  83
  84 #ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
  85 static void irq_event_handler(struct time_travel_event *ev)
  86 {
  87         struct irq_reg *reg = container_of(ev, struct irq_reg, event);
  88
  89         /* do nothing if suspended - just to cause a wakeup */
  90         if (irqs_suspended)
  91                 return;
  92
  93         generic_handle_irq(reg->irq);
  94 }
  95
  96 static bool irq_do_timetravel_handler(struct irq_entry *entry,
  97                                       enum um_irq_type t)
  98 {
  99         struct irq_reg *reg = &entry->reg[t];
 100
 101         if (!reg->timetravel_handler)
 102                 return false;
 103
 104         /* prevent nesting - we'll get it again later when we SIGIO ourselves */
 105         if (reg->pending_on_resume)
 106                 return true;
 107
 108         reg->timetravel_handler(reg->irq, entry->fd, reg->id, &reg->event);
 109
 110         if (!reg->event.pending)
 111                 return false;
 112
 113         if (irqs_suspended)
 114                 reg->pending_on_resume = true;
 115         return true;
 116 }
 117 #else
 118 static bool irq_do_timetravel_handler(struct irq_entry *entry,
 119                                       enum um_irq_type t)
 120 {
 121         return false;
 122 }
 123 #endif
 124
 125 static void sigio_reg_handler(int idx, struct irq_entry *entry, enum um_irq_type t,
 126                               struct uml_pt_regs *regs)
 127 {
 128         struct irq_reg *reg = &entry->reg[t];
 129
 130         if (!reg->events)
 131                 return;
 132
 133         if (os_epoll_triggered(idx, reg->events) <= 0)
 134                 return;
 135
 136         if (irq_do_timetravel_handler(entry, t))
 137                 return;
 138
 139         if (irqs_suspended)
 140                 return;
 141
 142         irq_io_loop(reg, regs);
 143 }
 144
 145 void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
 146 {
 147         struct irq_entry *irq_entry;
 148         int n, i;
 149
 150         if (irqs_suspended && !um_irq_timetravel_handler_used())
 151                 return;
 152
 153         while (1) {
 154                 /* This is now lockless - epoll keeps back-referencesto the irqs
 155                  * which have trigger it so there is no need to walk the irq
 156                  * list and lock it every time. We avoid locking by turning off
 157                  * IO for a specific fd by executing os_del_epoll_fd(fd) before
 158                  * we do any changes to the actual data structures
 159                  */
 160                 n = os_waiting_for_events_epoll();
 161
 162                 if (n <= 0) {
 163                         if (n == -EINTR)
 164                                 continue;
 165                         else
 166                                 break;
 167                 }
 168
 169                 for (i = 0; i < n ; i++) {
 170                         enum um_irq_type t;
 171
 172                         irq_entry = os_epoll_get_data_pointer(i);
 173
 174                         for (t = 0; t < NUM_IRQ_TYPES; t++)
 175                                 sigio_reg_handler(i, irq_entry, t, regs);
 176                 }
 177         }
 178
 179         if (!irqs_suspended)
 180                 free_irqs();
 181 }
 182
 183 static struct irq_entry *get_irq_entry_by_fd(int fd)
 184 {
 185         struct irq_entry *walk;
 186
 187         lockdep_assert_held(&irq_lock);
 188
 189         list_for_each_entry(walk, &active_fds, list) {
 190                 if (walk->fd == fd)
 191                         return walk;
 192         }
 193
 194         return NULL;
 195 }
 196
 197 static void free_irq_entry(struct irq_entry *to_free, bool remove)
 198 {
 199         if (!to_free)
 200                 return;
 201
 202         if (remove)
 203                 os_del_epoll_fd(to_free->fd);
 204         list_del(&to_free->list);
 205         kfree(to_free);
 206 }
 207
 208 static bool update_irq_entry(struct irq_entry *entry)
 209 {
 210         enum um_irq_type i;
 211         int events = 0;
 212
 213         for (i = 0; i < NUM_IRQ_TYPES; i++)
 214                 events |= entry->reg[i].events;
 215
 216         if (events) {
 217                 /* will modify (instead of add) if needed */
 218                 os_add_epoll_fd(events, entry->fd, entry);
 219                 return true;
 220         }
 221
 222         os_del_epoll_fd(entry->fd);
 223         return false;
 224 }
 225
 226 static void update_or_free_irq_entry(struct irq_entry *entry)
 227 {
 228         if (!update_irq_entry(entry))
 229                 free_irq_entry(entry, false);
 230 }
 231
 232 static int activate_fd(int irq, int fd, enum um_irq_type type, void *dev_id,
 233                        void (*timetravel_handler)(int, int, void *,
 234                                                   struct time_travel_event *))
 235 {
 236         struct irq_entry *irq_entry;
 237         int err, events = os_event_mask(type);
 238         unsigned long flags;
 239
 240         err = os_set_fd_async(fd);
 241         if (err < 0)
 242                 goto out;
 243
 244         spin_lock_irqsave(&irq_lock, flags);
 245         irq_entry = get_irq_entry_by_fd(fd);
 246         if (irq_entry) {
 247                 /* cannot register the same FD twice with the same type */
 248                 if (WARN_ON(irq_entry->reg[type].events)) {
 249                         err = -EALREADY;
 250                         goto out_unlock;
 251                 }
 252
 253                 /* temporarily disable to avoid IRQ-side locking */
 254                 os_del_epoll_fd(fd);
 255         } else {
 256                 irq_entry = kzalloc(sizeof(*irq_entry), GFP_ATOMIC);
 257                 if (!irq_entry) {
 258                         err = -ENOMEM;
 259                         goto out_unlock;
 260                 }
 261                 irq_entry->fd = fd;
 262                 list_add_tail(&irq_entry->list, &active_fds);
 263                 maybe_sigio_broken(fd);
 264         }
 265
 266         irq_entry->reg[type].id = dev_id;
 267         irq_entry->reg[type].irq = irq;
 268         irq_entry->reg[type].active = true;
 269         irq_entry->reg[type].events = events;
 270
 271 #ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
 272         if (um_irq_timetravel_handler_used()) {
 273                 irq_entry->reg[type].timetravel_handler = timetravel_handler;
 274                 irq_entry->reg[type].event.fn = irq_event_handler;
 275         }
 276 #endif
 277
 278         WARN_ON(!update_irq_entry(irq_entry));
 279         spin_unlock_irqrestore(&irq_lock, flags);
 280
 281         return 0;
 282 out_unlock:
 283         spin_unlock_irqrestore(&irq_lock, flags);
 284 out:
 285         return err;
 286 }
 287
 288 /*
 289  * Remove the entry or entries for a specific FD, if you
 290  * don't want to remove all the possible entries then use
 291  * um_free_irq() or deactivate_fd() instead.
 292  */
 293 void free_irq_by_fd(int fd)
 294 {
 295         struct irq_entry *to_free;
 296         unsigned long flags;
 297
 298         spin_lock_irqsave(&irq_lock, flags);
 299         to_free = get_irq_entry_by_fd(fd);
 300         free_irq_entry(to_free, true);
 301         spin_unlock_irqrestore(&irq_lock, flags);
 302 }
 303 EXPORT_SYMBOL(free_irq_by_fd);
 304
 305 static void free_irq_by_irq_and_dev(unsigned int irq, void *dev)
 306 {
 307         struct irq_entry *entry;
 308         unsigned long flags;
 309
 310         spin_lock_irqsave(&irq_lock, flags);
 311         list_for_each_entry(entry, &active_fds, list) {
 312                 enum um_irq_type i;
 313
 314                 for (i = 0; i < NUM_IRQ_TYPES; i++) {
 315                         struct irq_reg *reg = &entry->reg[i];
 316
 317                         if (!reg->events)
 318                                 continue;
 319                         if (reg->irq != irq)
 320                                 continue;
 321                         if (reg->id != dev)
 322                                 continue;
 323
 324                         os_del_epoll_fd(entry->fd);
 325                         reg->events = 0;
 326                         update_or_free_irq_entry(entry);
 327                         goto out;
 328                 }
 329         }
 330 out:
 331         spin_unlock_irqrestore(&irq_lock, flags);
 332 }
 333
 334 void deactivate_fd(int fd, int irqnum)
 335 {
 336         struct irq_entry *entry;
 337         unsigned long flags;
 338         enum um_irq_type i;
 339
 340         os_del_epoll_fd(fd);
 341
 342         spin_lock_irqsave(&irq_lock, flags);
 343         entry = get_irq_entry_by_fd(fd);
 344         if (!entry)
 345                 goto out;
 346
 347         for (i = 0; i < NUM_IRQ_TYPES; i++) {
 348                 if (!entry->reg[i].events)
 349                         continue;
 350                 if (entry->reg[i].irq == irqnum)
 351                         entry->reg[i].events = 0;
 352         }
 353
 354         update_or_free_irq_entry(entry);
 355 out:
 356         spin_unlock_irqrestore(&irq_lock, flags);
 357
 358         ignore_sigio_fd(fd);
 359 }
 360 EXPORT_SYMBOL(deactivate_fd);
 361
 362 /*
 363  * Called just before shutdown in order to provide a clean exec
 364  * environment in case the system is rebooting.  No locking because
 365  * that would cause a pointless shutdown hang if something hadn't
 366  * released the lock.
 367  */
 368 int deactivate_all_fds(void)
 369 {
 370         struct irq_entry *entry;
 371
 372         /* Stop IO. The IRQ loop has no lock so this is our
 373          * only way of making sure we are safe to dispose
 374          * of all IRQ handlers
 375          */
 376         os_set_ioignore();
 377
 378         /* we can no longer call kfree() here so just deactivate */
 379         list_for_each_entry(entry, &active_fds, list)
 380                 os_del_epoll_fd(entry->fd);
 381         os_close_epoll_fd();
 382         return 0;
 383 }
 384
 385 /*
 386  * do_IRQ handles all normal device IRQs (the special
 387  * SMP cross-CPU interrupts have their own specific
 388  * handlers).
 389  */
 390 unsigned int do_IRQ(int irq, struct uml_pt_regs *regs)
 391 {
 392         struct pt_regs *old_regs = set_irq_regs((struct pt_regs *)regs);
 393         irq_enter();
 394         generic_handle_irq(irq);
 395         irq_exit();
 396         set_irq_regs(old_regs);
 397         return 1;
 398 }
 399
 400 void um_free_irq(int irq, void *dev)
 401 {
 402         if (WARN(irq < 0 || irq > NR_IRQS, "freeing invalid irq %d", irq))
 403                 return;
 404
 405         free_irq_by_irq_and_dev(irq, dev);
 406         free_irq(irq, dev);
 407         clear_bit(irq, irqs_allocated);
 408 }
 409 EXPORT_SYMBOL(um_free_irq);
 410
 411 static int
 412 _um_request_irq(int irq, int fd, enum um_irq_type type,
 413                 irq_handler_t handler, unsigned long irqflags,
 414                 const char *devname, void *dev_id,
 415                 void (*timetravel_handler)(int, int, void *,
 416                                            struct time_travel_event *))
 417 {
 418         int err;
 419
 420         if (irq == UM_IRQ_ALLOC) {
 421                 int i;
 422
 423                 for (i = UM_FIRST_DYN_IRQ; i < NR_IRQS; i++) {
 424                         if (!test_and_set_bit(i, irqs_allocated)) {
 425                                 irq = i;
 426                                 break;
 427                         }
 428                 }
 429         }
 430
 431         if (irq < 0)
 432                 return -ENOSPC;
 433
 434         if (fd != -1) {
 435                 err = activate_fd(irq, fd, type, dev_id, timetravel_handler);
 436                 if (err)
 437                         goto error;
 438         }
 439
 440         err = request_irq(irq, handler, irqflags, devname, dev_id);
 441         if (err < 0)
 442                 goto error;
 443
 444         return irq;
 445 error:
 446         clear_bit(irq, irqs_allocated);
 447         return err;
 448 }
 449
 450 int um_request_irq(int irq, int fd, enum um_irq_type type,
 451                    irq_handler_t handler, unsigned long irqflags,
 452                    const char *devname, void *dev_id)
 453 {
 454         return _um_request_irq(irq, fd, type, handler, irqflags,
 455                                devname, dev_id, NULL);
 456 }
 457 EXPORT_SYMBOL(um_request_irq);
 458
 459 #ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
 460 int um_request_irq_tt(int irq, int fd, enum um_irq_type type,
 461                       irq_handler_t handler, unsigned long irqflags,
 462                       const char *devname, void *dev_id,
 463                       void (*timetravel_handler)(int, int, void *,
 464                                                  struct time_travel_event *))
 465 {
 466         return _um_request_irq(irq, fd, type, handler, irqflags,
 467                                devname, dev_id, timetravel_handler);
 468 }
 469 EXPORT_SYMBOL(um_request_irq_tt);
 470 #endif
 471
 472 #ifdef CONFIG_PM_SLEEP
 473 void um_irqs_suspend(void)
 474 {
 475         struct irq_entry *entry;
 476         unsigned long flags;
 477
 478         irqs_suspended = true;
 479
 480         spin_lock_irqsave(&irq_lock, flags);
 481         list_for_each_entry(entry, &active_fds, list) {
 482                 enum um_irq_type t;
 483                 bool clear = true;
 484
 485                 for (t = 0; t < NUM_IRQ_TYPES; t++) {
 486                         if (!entry->reg[t].events)
 487                                 continue;
 488
 489                         /*
 490                          * For the SIGIO_WRITE_IRQ, which is used to handle the
 491                          * SIGIO workaround thread, we need special handling:
 492                          * enable wake for it itself, but below we tell it about
 493                          * any FDs that should be suspended.
 494                          */
 495                         if (entry->reg[t].wakeup ||
 496                             entry->reg[t].irq == SIGIO_WRITE_IRQ
 497 #ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
 498                             || entry->reg[t].timetravel_handler
 499 #endif
 500                             ) {
 501                                 clear = false;
 502                                 break;
 503                         }
 504                 }
 505
 506                 if (clear) {
 507                         entry->suspended = true;
 508                         os_clear_fd_async(entry->fd);
 509                         entry->sigio_workaround =
 510                                 !__ignore_sigio_fd(entry->fd);
 511                 }
 512         }
 513         spin_unlock_irqrestore(&irq_lock, flags);
 514 }
 515
 516 void um_irqs_resume(void)
 517 {
 518         struct irq_entry *entry;
 519         unsigned long flags;
 520
 521
 522         local_irq_save(flags);
 523 #ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
 524         /*
 525          * We don't need to lock anything here since we're in resume
 526          * and nothing else is running, but have disabled IRQs so we
 527          * don't try anything else with the interrupt list from there.
 528          */
 529         list_for_each_entry(entry, &active_fds, list) {
 530                 enum um_irq_type t;
 531
 532                 for (t = 0; t < NUM_IRQ_TYPES; t++) {
 533                         struct irq_reg *reg = &entry->reg[t];
 534
 535                         if (reg->pending_on_resume) {
 536                                 irq_enter();
 537                                 generic_handle_irq(reg->irq);
 538                                 irq_exit();
 539                                 reg->pending_on_resume = false;
 540                         }
 541                 }
 542         }
 543 #endif
 544
 545         spin_lock(&irq_lock);
 546         list_for_each_entry(entry, &active_fds, list) {
 547                 if (entry->suspended) {
 548                         int err = os_set_fd_async(entry->fd);
 549
 550                         WARN(err < 0, "os_set_fd_async returned %d\n", err);
 551                         entry->suspended = false;
 552
 553                         if (entry->sigio_workaround) {
 554                                 err = __add_sigio_fd(entry->fd);
 555                                 WARN(err < 0, "add_sigio_returned %d\n", err);
 556                         }
 557                 }
 558         }
 559         spin_unlock_irqrestore(&irq_lock, flags);
 560
 561         irqs_suspended = false;
 562         send_sigio_to_self();
 563 }
 564
 565 static int normal_irq_set_wake(struct irq_data *d, unsigned int on)
 566 {
 567         struct irq_entry *entry;
 568         unsigned long flags;
 569
 570         spin_lock_irqsave(&irq_lock, flags);
 571         list_for_each_entry(entry, &active_fds, list) {
 572                 enum um_irq_type t;
 573
 574                 for (t = 0; t < NUM_IRQ_TYPES; t++) {
 575                         if (!entry->reg[t].events)
 576                                 continue;
 577
 578                         if (entry->reg[t].irq != d->irq)
 579                                 continue;
 580                         entry->reg[t].wakeup = on;
 581                         goto unlock;
 582                 }
 583         }
 584 unlock:
 585         spin_unlock_irqrestore(&irq_lock, flags);
 586         return 0;
 587 }
 588 #else
 589 #define normal_irq_set_wake NULL
 590 #endif
 591
 592 /*
 593  * irq_chip must define at least enable/disable and ack when
 594  * the edge handler is used.
 595  */
 596 static void dummy(struct irq_data *d)
 597 {
 598 }
 599
 600 /* This is used for everything other than the timer. */
 601 static struct irq_chip normal_irq_type = {
 602         .name = "SIGIO",
 603         .irq_disable = dummy,
 604         .irq_enable = dummy,
 605         .irq_ack = dummy,
 606         .irq_mask = dummy,
 607         .irq_unmask = dummy,
 608         .irq_set_wake = normal_irq_set_wake,
 609 };
 610
 611 static struct irq_chip alarm_irq_type = {
 612         .name = "SIGALRM",
 613         .irq_disable = dummy,
 614         .irq_enable = dummy,
 615         .irq_ack = dummy,
 616         .irq_mask = dummy,
 617         .irq_unmask = dummy,
 618 };
 619
 620 void __init init_IRQ(void)
 621 {
 622         int i;
 623
 624         irq_set_chip_and_handler(TIMER_IRQ, &alarm_irq_type, handle_edge_irq);
 625
 626         for (i = 1; i < NR_IRQS; i++)
 627                 irq_set_chip_and_handler(i, &normal_irq_type, handle_edge_irq);
 628         /* Initialize EPOLL Loop */
 629         os_setup_epoll();
 630 }
 631
 632 /*
 633  * IRQ stack entry and exit:
 634  *
 635  * Unlike i386, UML doesn't receive IRQs on the normal kernel stack
 636  * and switch over to the IRQ stack after some preparation.  We use
 637  * sigaltstack to receive signals on a separate stack from the start.
 638  * These two functions make sure the rest of the kernel won't be too
 639  * upset by being on a different stack.  The IRQ stack has a
 640  * thread_info structure at the bottom so that current et al continue
 641  * to work.
 642  *
 643  * to_irq_stack copies the current task's thread_info to the IRQ stack
 644  * thread_info and sets the tasks's stack to point to the IRQ stack.
 645  *
 646  * from_irq_stack copies the thread_info struct back (flags may have
 647  * been modified) and resets the task's stack pointer.
 648  *
 649  * Tricky bits -
 650  *
 651  * What happens when two signals race each other?  UML doesn't block
 652  * signals with sigprocmask, SA_DEFER, or sa_mask, so a second signal
 653  * could arrive while a previous one is still setting up the
 654  * thread_info.
 655  *
 656  * There are three cases -
 657  *     The first interrupt on the stack - sets up the thread_info and
 658  * handles the interrupt
 659  *     A nested interrupt interrupting the copying of the thread_info -
 660  * can't handle the interrupt, as the stack is in an unknown state
 661  *     A nested interrupt not interrupting the copying of the
 662  * thread_info - doesn't do any setup, just handles the interrupt
 663  *
 664  * The first job is to figure out whether we interrupted stack setup.
 665  * This is done by xchging the signal mask with thread_info->pending.
 666  * If the value that comes back is zero, then there is no setup in
 667  * progress, and the interrupt can be handled.  If the value is
 668  * non-zero, then there is stack setup in progress.  In order to have
 669  * the interrupt handled, we leave our signal in the mask, and it will
 670  * be handled by the upper handler after it has set up the stack.
 671  *
 672  * Next is to figure out whether we are the outer handler or a nested
 673  * one.  As part of setting up the stack, thread_info->real_thread is
 674  * set to non-NULL (and is reset to NULL on exit).  This is the
 675  * nesting indicator.  If it is non-NULL, then the stack is already
 676  * set up and the handler can run.
 677  */
 678
 679 static unsigned long pending_mask;
 680
 681 unsigned long to_irq_stack(unsigned long *mask_out)
 682 {
 683         struct thread_info *ti;
 684         unsigned long mask, old;
 685         int nested;
 686
 687         mask = xchg(&pending_mask, *mask_out);
 688         if (mask != 0) {
 689                 /*
 690                  * If any interrupts come in at this point, we want to
 691                  * make sure that their bits aren't lost by our
 692                  * putting our bit in.  So, this loop accumulates bits
 693                  * until xchg returns the same value that we put in.
 694                  * When that happens, there were no new interrupts,
 695                  * and pending_mask contains a bit for each interrupt
 696                  * that came in.
 697                  */
 698                 old = *mask_out;
 699                 do {
 700                         old |= mask;
 701                         mask = xchg(&pending_mask, old);
 702                 } while (mask != old);
 703                 return 1;
 704         }
 705
 706         ti = current_thread_info();
 707         nested = (ti->real_thread != NULL);
 708         if (!nested) {
 709                 struct task_struct *task;
 710                 struct thread_info *tti;
 711
 712                 task = cpu_tasks[ti->cpu].task;
 713                 tti = task_thread_info(task);
 714
 715                 *ti = *tti;
 716                 ti->real_thread = tti;
 717                 task->stack = ti;
 718         }
 719
 720         mask = xchg(&pending_mask, 0);
 721         *mask_out |= mask | nested;
 722         return 0;
 723 }
 724
 725 unsigned long from_irq_stack(int nested)
 726 {
 727         struct thread_info *ti, *to;
 728         unsigned long mask;
 729
 730         ti = current_thread_info();
 731
 732         pending_mask = 1;
 733
 734         to = ti->real_thread;
 735         current->stack = to;
 736         ti->real_thread = NULL;
 737         *to = *ti;
 738
 739         mask = xchg(&pending_mask, 0);
 740         return mask & ~1;
 741 }
 742