linux/kernel/marker.c
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   1/*
   2 * Copyright (C) 2007 Mathieu Desnoyers
   3 *
   4 * This program is free software; you can redistribute it and/or modify
   5 * it under the terms of the GNU General Public License as published by
   6 * the Free Software Foundation; either version 2 of the License, or
   7 * (at your option) any later version.
   8 *
   9 * This program is distributed in the hope that it will be useful,
  10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 * GNU General Public License for more details.
  13 *
  14 * You should have received a copy of the GNU General Public License
  15 * along with this program; if not, write to the Free Software
  16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17 */
  18#include <linux/module.h>
  19#include <linux/mutex.h>
  20#include <linux/types.h>
  21#include <linux/jhash.h>
  22#include <linux/list.h>
  23#include <linux/rcupdate.h>
  24#include <linux/marker.h>
  25#include <linux/err.h>
  26
  27extern struct marker __start___markers[];
  28extern struct marker __stop___markers[];
  29
  30/* Set to 1 to enable marker debug output */
  31const int marker_debug;
  32
  33/*
  34 * markers_mutex nests inside module_mutex. Markers mutex protects the builtin
  35 * and module markers and the hash table.
  36 */
  37static DEFINE_MUTEX(markers_mutex);
  38
  39/*
  40 * Marker hash table, containing the active markers.
  41 * Protected by module_mutex.
  42 */
  43#define MARKER_HASH_BITS 6
  44#define MARKER_TABLE_SIZE (1 << MARKER_HASH_BITS)
  45
  46/*
  47 * Note about RCU :
  48 * It is used to make sure every handler has finished using its private data
  49 * between two consecutive operation (add or remove) on a given marker.  It is
  50 * also used to delay the free of multiple probes array until a quiescent state
  51 * is reached.
  52 * marker entries modifications are protected by the markers_mutex.
  53 */
  54struct marker_entry {
  55        struct hlist_node hlist;
  56        char *format;
  57        void (*call)(const struct marker *mdata,        /* Probe wrapper */
  58                void *call_private, const char *fmt, ...);
  59        struct marker_probe_closure single;
  60        struct marker_probe_closure *multi;
  61        int refcount;   /* Number of times armed. 0 if disarmed. */
  62        struct rcu_head rcu;
  63        void *oldptr;
  64        unsigned char rcu_pending:1;
  65        unsigned char ptype:1;
  66        char name[0];   /* Contains name'\0'format'\0' */
  67};
  68
  69static struct hlist_head marker_table[MARKER_TABLE_SIZE];
  70
  71/**
  72 * __mark_empty_function - Empty probe callback
  73 * @probe_private: probe private data
  74 * @call_private: call site private data
  75 * @fmt: format string
  76 * @...: variable argument list
  77 *
  78 * Empty callback provided as a probe to the markers. By providing this to a
  79 * disabled marker, we make sure the  execution flow is always valid even
  80 * though the function pointer change and the marker enabling are two distinct
  81 * operations that modifies the execution flow of preemptible code.
  82 */
  83void __mark_empty_function(void *probe_private, void *call_private,
  84        const char *fmt, va_list *args)
  85{
  86}
  87EXPORT_SYMBOL_GPL(__mark_empty_function);
  88
  89/*
  90 * marker_probe_cb Callback that prepares the variable argument list for probes.
  91 * @mdata: pointer of type struct marker
  92 * @call_private: caller site private data
  93 * @fmt: format string
  94 * @...:  Variable argument list.
  95 *
  96 * Since we do not use "typical" pointer based RCU in the 1 argument case, we
  97 * need to put a full smp_rmb() in this branch. This is why we do not use
  98 * rcu_dereference() for the pointer read.
  99 */
 100void marker_probe_cb(const struct marker *mdata, void *call_private,
 101        const char *fmt, ...)
 102{
 103        va_list args;
 104        char ptype;
 105
 106        /*
 107         * preempt_disable does two things : disabling preemption to make sure
 108         * the teardown of the callbacks can be done correctly when they are in
 109         * modules and they insure RCU read coherency.
 110         */
 111        preempt_disable();
 112        ptype = mdata->ptype;
 113        if (likely(!ptype)) {
 114                marker_probe_func *func;
 115                /* Must read the ptype before ptr. They are not data dependant,
 116                 * so we put an explicit smp_rmb() here. */
 117                smp_rmb();
 118                func = mdata->single.func;
 119                /* Must read the ptr before private data. They are not data
 120                 * dependant, so we put an explicit smp_rmb() here. */
 121                smp_rmb();
 122                va_start(args, fmt);
 123                func(mdata->single.probe_private, call_private, fmt, &args);
 124                va_end(args);
 125        } else {
 126                struct marker_probe_closure *multi;
 127                int i;
 128                /*
 129                 * multi points to an array, therefore accessing the array
 130                 * depends on reading multi. However, even in this case,
 131                 * we must insure that the pointer is read _before_ the array
 132                 * data. Same as rcu_dereference, but we need a full smp_rmb()
 133                 * in the fast path, so put the explicit barrier here.
 134                 */
 135                smp_read_barrier_depends();
 136                multi = mdata->multi;
 137                for (i = 0; multi[i].func; i++) {
 138                        va_start(args, fmt);
 139                        multi[i].func(multi[i].probe_private, call_private, fmt,
 140                                &args);
 141                        va_end(args);
 142                }
 143        }
 144        preempt_enable();
 145}
 146EXPORT_SYMBOL_GPL(marker_probe_cb);
 147
 148/*
 149 * marker_probe_cb Callback that does not prepare the variable argument list.
 150 * @mdata: pointer of type struct marker
 151 * @call_private: caller site private data
 152 * @fmt: format string
 153 * @...:  Variable argument list.
 154 *
 155 * Should be connected to markers "MARK_NOARGS".
 156 */
 157void marker_probe_cb_noarg(const struct marker *mdata,
 158        void *call_private, const char *fmt, ...)
 159{
 160        va_list args;   /* not initialized */
 161        char ptype;
 162
 163        preempt_disable();
 164        ptype = mdata->ptype;
 165        if (likely(!ptype)) {
 166                marker_probe_func *func;
 167                /* Must read the ptype before ptr. They are not data dependant,
 168                 * so we put an explicit smp_rmb() here. */
 169                smp_rmb();
 170                func = mdata->single.func;
 171                /* Must read the ptr before private data. They are not data
 172                 * dependant, so we put an explicit smp_rmb() here. */
 173                smp_rmb();
 174                func(mdata->single.probe_private, call_private, fmt, &args);
 175        } else {
 176                struct marker_probe_closure *multi;
 177                int i;
 178                /*
 179                 * multi points to an array, therefore accessing the array
 180                 * depends on reading multi. However, even in this case,
 181                 * we must insure that the pointer is read _before_ the array
 182                 * data. Same as rcu_dereference, but we need a full smp_rmb()
 183                 * in the fast path, so put the explicit barrier here.
 184                 */
 185                smp_read_barrier_depends();
 186                multi = mdata->multi;
 187                for (i = 0; multi[i].func; i++)
 188                        multi[i].func(multi[i].probe_private, call_private, fmt,
 189                                &args);
 190        }
 191        preempt_enable();
 192}
 193EXPORT_SYMBOL_GPL(marker_probe_cb_noarg);
 194
 195static void free_old_closure(struct rcu_head *head)
 196{
 197        struct marker_entry *entry = container_of(head,
 198                struct marker_entry, rcu);
 199        kfree(entry->oldptr);
 200        /* Make sure we free the data before setting the pending flag to 0 */
 201        smp_wmb();
 202        entry->rcu_pending = 0;
 203}
 204
 205static void debug_print_probes(struct marker_entry *entry)
 206{
 207        int i;
 208
 209        if (!marker_debug)
 210                return;
 211
 212        if (!entry->ptype) {
 213                printk(KERN_DEBUG "Single probe : %p %p\n",
 214                        entry->single.func,
 215                        entry->single.probe_private);
 216        } else {
 217                for (i = 0; entry->multi[i].func; i++)
 218                        printk(KERN_DEBUG "Multi probe %d : %p %p\n", i,
 219                                entry->multi[i].func,
 220                                entry->multi[i].probe_private);
 221        }
 222}
 223
 224static struct marker_probe_closure *
 225marker_entry_add_probe(struct marker_entry *entry,
 226                marker_probe_func *probe, void *probe_private)
 227{
 228        int nr_probes = 0;
 229        struct marker_probe_closure *old, *new;
 230
 231        WARN_ON(!probe);
 232
 233        debug_print_probes(entry);
 234        old = entry->multi;
 235        if (!entry->ptype) {
 236                if (entry->single.func == probe &&
 237                                entry->single.probe_private == probe_private)
 238                        return ERR_PTR(-EBUSY);
 239                if (entry->single.func == __mark_empty_function) {
 240                        /* 0 -> 1 probes */
 241                        entry->single.func = probe;
 242                        entry->single.probe_private = probe_private;
 243                        entry->refcount = 1;
 244                        entry->ptype = 0;
 245                        debug_print_probes(entry);
 246                        return NULL;
 247                } else {
 248                        /* 1 -> 2 probes */
 249                        nr_probes = 1;
 250                        old = NULL;
 251                }
 252        } else {
 253                /* (N -> N+1), (N != 0, 1) probes */
 254                for (nr_probes = 0; old[nr_probes].func; nr_probes++)
 255                        if (old[nr_probes].func == probe
 256                                        && old[nr_probes].probe_private
 257                                                == probe_private)
 258                                return ERR_PTR(-EBUSY);
 259        }
 260        /* + 2 : one for new probe, one for NULL func */
 261        new = kzalloc((nr_probes + 2) * sizeof(struct marker_probe_closure),
 262                        GFP_KERNEL);
 263        if (new == NULL)
 264                return ERR_PTR(-ENOMEM);
 265        if (!old)
 266                new[0] = entry->single;
 267        else
 268                memcpy(new, old,
 269                        nr_probes * sizeof(struct marker_probe_closure));
 270        new[nr_probes].func = probe;
 271        new[nr_probes].probe_private = probe_private;
 272        entry->refcount = nr_probes + 1;
 273        entry->multi = new;
 274        entry->ptype = 1;
 275        debug_print_probes(entry);
 276        return old;
 277}
 278
 279static struct marker_probe_closure *
 280marker_entry_remove_probe(struct marker_entry *entry,
 281                marker_probe_func *probe, void *probe_private)
 282{
 283        int nr_probes = 0, nr_del = 0, i;
 284        struct marker_probe_closure *old, *new;
 285
 286        old = entry->multi;
 287
 288        debug_print_probes(entry);
 289        if (!entry->ptype) {
 290                /* 0 -> N is an error */
 291                WARN_ON(entry->single.func == __mark_empty_function);
 292                /* 1 -> 0 probes */
 293                WARN_ON(probe && entry->single.func != probe);
 294                WARN_ON(entry->single.probe_private != probe_private);
 295                entry->single.func = __mark_empty_function;
 296                entry->refcount = 0;
 297                entry->ptype = 0;
 298                debug_print_probes(entry);
 299                return NULL;
 300        } else {
 301                /* (N -> M), (N > 1, M >= 0) probes */
 302                for (nr_probes = 0; old[nr_probes].func; nr_probes++) {
 303                        if ((!probe || old[nr_probes].func == probe)
 304                                        && old[nr_probes].probe_private
 305                                                == probe_private)
 306                                nr_del++;
 307                }
 308        }
 309
 310        if (nr_probes - nr_del == 0) {
 311                /* N -> 0, (N > 1) */
 312                entry->single.func = __mark_empty_function;
 313                entry->refcount = 0;
 314                entry->ptype = 0;
 315        } else if (nr_probes - nr_del == 1) {
 316                /* N -> 1, (N > 1) */
 317                for (i = 0; old[i].func; i++)
 318                        if ((probe && old[i].func != probe) ||
 319                                        old[i].probe_private != probe_private)
 320                                entry->single = old[i];
 321                entry->refcount = 1;
 322                entry->ptype = 0;
 323        } else {
 324                int j = 0;
 325                /* N -> M, (N > 1, M > 1) */
 326                /* + 1 for NULL */
 327                new = kzalloc((nr_probes - nr_del + 1)
 328                        * sizeof(struct marker_probe_closure), GFP_KERNEL);
 329                if (new == NULL)
 330                        return ERR_PTR(-ENOMEM);
 331                for (i = 0; old[i].func; i++)
 332                        if ((probe && old[i].func != probe) ||
 333                                        old[i].probe_private != probe_private)
 334                                new[j++] = old[i];
 335                entry->refcount = nr_probes - nr_del;
 336                entry->ptype = 1;
 337                entry->multi = new;
 338        }
 339        debug_print_probes(entry);
 340        return old;
 341}
 342
 343/*
 344 * Get marker if the marker is present in the marker hash table.
 345 * Must be called with markers_mutex held.
 346 * Returns NULL if not present.
 347 */
 348static struct marker_entry *get_marker(const char *name)
 349{
 350        struct hlist_head *head;
 351        struct hlist_node *node;
 352        struct marker_entry *e;
 353        u32 hash = jhash(name, strlen(name), 0);
 354
 355        head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
 356        hlist_for_each_entry(e, node, head, hlist) {
 357                if (!strcmp(name, e->name))
 358                        return e;
 359        }
 360        return NULL;
 361}
 362
 363/*
 364 * Add the marker to the marker hash table. Must be called with markers_mutex
 365 * held.
 366 */
 367static struct marker_entry *add_marker(const char *name, const char *format)
 368{
 369        struct hlist_head *head;
 370        struct hlist_node *node;
 371        struct marker_entry *e;
 372        size_t name_len = strlen(name) + 1;
 373        size_t format_len = 0;
 374        u32 hash = jhash(name, name_len-1, 0);
 375
 376        if (format)
 377                format_len = strlen(format) + 1;
 378        head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
 379        hlist_for_each_entry(e, node, head, hlist) {
 380                if (!strcmp(name, e->name)) {
 381                        printk(KERN_NOTICE
 382                                "Marker %s busy\n", name);
 383                        return ERR_PTR(-EBUSY); /* Already there */
 384                }
 385        }
 386        /*
 387         * Using kmalloc here to allocate a variable length element. Could
 388         * cause some memory fragmentation if overused.
 389         */
 390        e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
 391                        GFP_KERNEL);
 392        if (!e)
 393                return ERR_PTR(-ENOMEM);
 394        memcpy(&e->name[0], name, name_len);
 395        if (format) {
 396                e->format = &e->name[name_len];
 397                memcpy(e->format, format, format_len);
 398                if (strcmp(e->format, MARK_NOARGS) == 0)
 399                        e->call = marker_probe_cb_noarg;
 400                else
 401                        e->call = marker_probe_cb;
 402                trace_mark(core_marker_format, "name %s format %s",
 403                                e->name, e->format);
 404        } else {
 405                e->format = NULL;
 406                e->call = marker_probe_cb;
 407        }
 408        e->single.func = __mark_empty_function;
 409        e->single.probe_private = NULL;
 410        e->multi = NULL;
 411        e->ptype = 0;
 412        e->refcount = 0;
 413        e->rcu_pending = 0;
 414        hlist_add_head(&e->hlist, head);
 415        return e;
 416}
 417
 418/*
 419 * Remove the marker from the marker hash table. Must be called with mutex_lock
 420 * held.
 421 */
 422static int remove_marker(const char *name)
 423{
 424        struct hlist_head *head;
 425        struct hlist_node *node;
 426        struct marker_entry *e;
 427        int found = 0;
 428        size_t len = strlen(name) + 1;
 429        u32 hash = jhash(name, len-1, 0);
 430
 431        head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
 432        hlist_for_each_entry(e, node, head, hlist) {
 433                if (!strcmp(name, e->name)) {
 434                        found = 1;
 435                        break;
 436                }
 437        }
 438        if (!found)
 439                return -ENOENT;
 440        if (e->single.func != __mark_empty_function)
 441                return -EBUSY;
 442        hlist_del(&e->hlist);
 443        /* Make sure the call_rcu has been executed */
 444        if (e->rcu_pending)
 445                rcu_barrier();
 446        kfree(e);
 447        return 0;
 448}
 449
 450/*
 451 * Set the mark_entry format to the format found in the element.
 452 */
 453static int marker_set_format(struct marker_entry **entry, const char *format)
 454{
 455        struct marker_entry *e;
 456        size_t name_len = strlen((*entry)->name) + 1;
 457        size_t format_len = strlen(format) + 1;
 458
 459
 460        e = kmalloc(sizeof(struct marker_entry) + name_len + format_len,
 461                        GFP_KERNEL);
 462        if (!e)
 463                return -ENOMEM;
 464        memcpy(&e->name[0], (*entry)->name, name_len);
 465        e->format = &e->name[name_len];
 466        memcpy(e->format, format, format_len);
 467        if (strcmp(e->format, MARK_NOARGS) == 0)
 468                e->call = marker_probe_cb_noarg;
 469        else
 470                e->call = marker_probe_cb;
 471        e->single = (*entry)->single;
 472        e->multi = (*entry)->multi;
 473        e->ptype = (*entry)->ptype;
 474        e->refcount = (*entry)->refcount;
 475        e->rcu_pending = 0;
 476        hlist_add_before(&e->hlist, &(*entry)->hlist);
 477        hlist_del(&(*entry)->hlist);
 478        /* Make sure the call_rcu has been executed */
 479        if ((*entry)->rcu_pending)
 480                rcu_barrier();
 481        kfree(*entry);
 482        *entry = e;
 483        trace_mark(core_marker_format, "name %s format %s",
 484                        e->name, e->format);
 485        return 0;
 486}
 487
 488/*
 489 * Sets the probe callback corresponding to one marker.
 490 */
 491static int set_marker(struct marker_entry **entry, struct marker *elem,
 492                int active)
 493{
 494        int ret;
 495        WARN_ON(strcmp((*entry)->name, elem->name) != 0);
 496
 497        if ((*entry)->format) {
 498                if (strcmp((*entry)->format, elem->format) != 0) {
 499                        printk(KERN_NOTICE
 500                                "Format mismatch for probe %s "
 501                                "(%s), marker (%s)\n",
 502                                (*entry)->name,
 503                                (*entry)->format,
 504                                elem->format);
 505                        return -EPERM;
 506                }
 507        } else {
 508                ret = marker_set_format(entry, elem->format);
 509                if (ret)
 510                        return ret;
 511        }
 512
 513        /*
 514         * probe_cb setup (statically known) is done here. It is
 515         * asynchronous with the rest of execution, therefore we only
 516         * pass from a "safe" callback (with argument) to an "unsafe"
 517         * callback (does not set arguments).
 518         */
 519        elem->call = (*entry)->call;
 520        /*
 521         * Sanity check :
 522         * We only update the single probe private data when the ptr is
 523         * set to a _non_ single probe! (0 -> 1 and N -> 1, N != 1)
 524         */
 525        WARN_ON(elem->single.func != __mark_empty_function
 526                && elem->single.probe_private
 527                != (*entry)->single.probe_private &&
 528                !elem->ptype);
 529        elem->single.probe_private = (*entry)->single.probe_private;
 530        /*
 531         * Make sure the private data is valid when we update the
 532         * single probe ptr.
 533         */
 534        smp_wmb();
 535        elem->single.func = (*entry)->single.func;
 536        /*
 537         * We also make sure that the new probe callbacks array is consistent
 538         * before setting a pointer to it.
 539         */
 540        rcu_assign_pointer(elem->multi, (*entry)->multi);
 541        /*
 542         * Update the function or multi probe array pointer before setting the
 543         * ptype.
 544         */
 545        smp_wmb();
 546        elem->ptype = (*entry)->ptype;
 547        elem->state = active;
 548
 549        return 0;
 550}
 551
 552/*
 553 * Disable a marker and its probe callback.
 554 * Note: only waiting an RCU period after setting elem->call to the empty
 555 * function insures that the original callback is not used anymore. This insured
 556 * by preempt_disable around the call site.
 557 */
 558static void disable_marker(struct marker *elem)
 559{
 560        /* leave "call" as is. It is known statically. */
 561        elem->state = 0;
 562        elem->single.func = __mark_empty_function;
 563        /* Update the function before setting the ptype */
 564        smp_wmb();
 565        elem->ptype = 0;        /* single probe */
 566        /*
 567         * Leave the private data and id there, because removal is racy and
 568         * should be done only after an RCU period. These are never used until
 569         * the next initialization anyway.
 570         */
 571}
 572
 573/**
 574 * marker_update_probe_range - Update a probe range
 575 * @begin: beginning of the range
 576 * @end: end of the range
 577 *
 578 * Updates the probe callback corresponding to a range of markers.
 579 */
 580void marker_update_probe_range(struct marker *begin,
 581        struct marker *end)
 582{
 583        struct marker *iter;
 584        struct marker_entry *mark_entry;
 585
 586        mutex_lock(&markers_mutex);
 587        for (iter = begin; iter < end; iter++) {
 588                mark_entry = get_marker(iter->name);
 589                if (mark_entry) {
 590                        set_marker(&mark_entry, iter,
 591                                        !!mark_entry->refcount);
 592                        /*
 593                         * ignore error, continue
 594                         */
 595                } else {
 596                        disable_marker(iter);
 597                }
 598        }
 599        mutex_unlock(&markers_mutex);
 600}
 601
 602/*
 603 * Update probes, removing the faulty probes.
 604 *
 605 * Internal callback only changed before the first probe is connected to it.
 606 * Single probe private data can only be changed on 0 -> 1 and 2 -> 1
 607 * transitions.  All other transitions will leave the old private data valid.
 608 * This makes the non-atomicity of the callback/private data updates valid.
 609 *
 610 * "special case" updates :
 611 * 0 -> 1 callback
 612 * 1 -> 0 callback
 613 * 1 -> 2 callbacks
 614 * 2 -> 1 callbacks
 615 * Other updates all behave the same, just like the 2 -> 3 or 3 -> 2 updates.
 616 * Site effect : marker_set_format may delete the marker entry (creating a
 617 * replacement).
 618 */
 619static void marker_update_probes(void)
 620{
 621        /* Core kernel markers */
 622        marker_update_probe_range(__start___markers, __stop___markers);
 623        /* Markers in modules. */
 624        module_update_markers();
 625}
 626
 627/**
 628 * marker_probe_register -  Connect a probe to a marker
 629 * @name: marker name
 630 * @format: format string
 631 * @probe: probe handler
 632 * @probe_private: probe private data
 633 *
 634 * private data must be a valid allocated memory address, or NULL.
 635 * Returns 0 if ok, error value on error.
 636 * The probe address must at least be aligned on the architecture pointer size.
 637 */
 638int marker_probe_register(const char *name, const char *format,
 639                        marker_probe_func *probe, void *probe_private)
 640{
 641        struct marker_entry *entry;
 642        int ret = 0;
 643        struct marker_probe_closure *old;
 644
 645        mutex_lock(&markers_mutex);
 646        entry = get_marker(name);
 647        if (!entry) {
 648                entry = add_marker(name, format);
 649                if (IS_ERR(entry)) {
 650                        ret = PTR_ERR(entry);
 651                        goto end;
 652                }
 653        }
 654        /*
 655         * If we detect that a call_rcu is pending for this marker,
 656         * make sure it's executed now.
 657         */
 658        if (entry->rcu_pending)
 659                rcu_barrier();
 660        old = marker_entry_add_probe(entry, probe, probe_private);
 661        if (IS_ERR(old)) {
 662                ret = PTR_ERR(old);
 663                goto end;
 664        }
 665        mutex_unlock(&markers_mutex);
 666        marker_update_probes();         /* may update entry */
 667        mutex_lock(&markers_mutex);
 668        entry = get_marker(name);
 669        WARN_ON(!entry);
 670        entry->oldptr = old;
 671        entry->rcu_pending = 1;
 672        /* write rcu_pending before calling the RCU callback */
 673        smp_wmb();
 674#ifdef CONFIG_PREEMPT_RCU
 675        synchronize_sched();    /* Until we have the call_rcu_sched() */
 676#endif
 677        call_rcu(&entry->rcu, free_old_closure);
 678end:
 679        mutex_unlock(&markers_mutex);
 680        return ret;
 681}
 682EXPORT_SYMBOL_GPL(marker_probe_register);
 683
 684/**
 685 * marker_probe_unregister -  Disconnect a probe from a marker
 686 * @name: marker name
 687 * @probe: probe function pointer
 688 * @probe_private: probe private data
 689 *
 690 * Returns the private data given to marker_probe_register, or an ERR_PTR().
 691 * We do not need to call a synchronize_sched to make sure the probes have
 692 * finished running before doing a module unload, because the module unload
 693 * itself uses stop_machine(), which insures that every preempt disabled section
 694 * have finished.
 695 */
 696int marker_probe_unregister(const char *name,
 697        marker_probe_func *probe, void *probe_private)
 698{
 699        struct marker_entry *entry;
 700        struct marker_probe_closure *old;
 701        int ret = -ENOENT;
 702
 703        mutex_lock(&markers_mutex);
 704        entry = get_marker(name);
 705        if (!entry)
 706                goto end;
 707        if (entry->rcu_pending)
 708                rcu_barrier();
 709        old = marker_entry_remove_probe(entry, probe, probe_private);
 710        mutex_unlock(&markers_mutex);
 711        marker_update_probes();         /* may update entry */
 712        mutex_lock(&markers_mutex);
 713        entry = get_marker(name);
 714        if (!entry)
 715                goto end;
 716        entry->oldptr = old;
 717        entry->rcu_pending = 1;
 718        /* write rcu_pending before calling the RCU callback */
 719        smp_wmb();
 720#ifdef CONFIG_PREEMPT_RCU
 721        synchronize_sched();    /* Until we have the call_rcu_sched() */
 722#endif
 723        call_rcu(&entry->rcu, free_old_closure);
 724        remove_marker(name);    /* Ignore busy error message */
 725        ret = 0;
 726end:
 727        mutex_unlock(&markers_mutex);
 728        return ret;
 729}
 730EXPORT_SYMBOL_GPL(marker_probe_unregister);
 731
 732static struct marker_entry *
 733get_marker_from_private_data(marker_probe_func *probe, void *probe_private)
 734{
 735        struct marker_entry *entry;
 736        unsigned int i;
 737        struct hlist_head *head;
 738        struct hlist_node *node;
 739
 740        for (i = 0; i < MARKER_TABLE_SIZE; i++) {
 741                head = &marker_table[i];
 742                hlist_for_each_entry(entry, node, head, hlist) {
 743                        if (!entry->ptype) {
 744                                if (entry->single.func == probe
 745                                                && entry->single.probe_private
 746                                                == probe_private)
 747                                        return entry;
 748                        } else {
 749                                struct marker_probe_closure *closure;
 750                                closure = entry->multi;
 751                                for (i = 0; closure[i].func; i++) {
 752                                        if (closure[i].func == probe &&
 753                                                        closure[i].probe_private
 754                                                        == probe_private)
 755                                                return entry;
 756                                }
 757                        }
 758                }
 759        }
 760        return NULL;
 761}
 762
 763/**
 764 * marker_probe_unregister_private_data -  Disconnect a probe from a marker
 765 * @probe: probe function
 766 * @probe_private: probe private data
 767 *
 768 * Unregister a probe by providing the registered private data.
 769 * Only removes the first marker found in hash table.
 770 * Return 0 on success or error value.
 771 * We do not need to call a synchronize_sched to make sure the probes have
 772 * finished running before doing a module unload, because the module unload
 773 * itself uses stop_machine(), which insures that every preempt disabled section
 774 * have finished.
 775 */
 776int marker_probe_unregister_private_data(marker_probe_func *probe,
 777                void *probe_private)
 778{
 779        struct marker_entry *entry;
 780        int ret = 0;
 781        struct marker_probe_closure *old;
 782
 783        mutex_lock(&markers_mutex);
 784        entry = get_marker_from_private_data(probe, probe_private);
 785        if (!entry) {
 786                ret = -ENOENT;
 787                goto end;
 788        }
 789        if (entry->rcu_pending)
 790                rcu_barrier();
 791        old = marker_entry_remove_probe(entry, NULL, probe_private);
 792        mutex_unlock(&markers_mutex);
 793        marker_update_probes();         /* may update entry */
 794        mutex_lock(&markers_mutex);
 795        entry = get_marker_from_private_data(probe, probe_private);
 796        WARN_ON(!entry);
 797        entry->oldptr = old;
 798        entry->rcu_pending = 1;
 799        /* write rcu_pending before calling the RCU callback */
 800        smp_wmb();
 801#ifdef CONFIG_PREEMPT_RCU
 802        synchronize_sched();    /* Until we have the call_rcu_sched() */
 803#endif
 804        call_rcu(&entry->rcu, free_old_closure);
 805        remove_marker(entry->name);     /* Ignore busy error message */
 806end:
 807        mutex_unlock(&markers_mutex);
 808        return ret;
 809}
 810EXPORT_SYMBOL_GPL(marker_probe_unregister_private_data);
 811
 812/**
 813 * marker_get_private_data - Get a marker's probe private data
 814 * @name: marker name
 815 * @probe: probe to match
 816 * @num: get the nth matching probe's private data
 817 *
 818 * Returns the nth private data pointer (starting from 0) matching, or an
 819 * ERR_PTR.
 820 * Returns the private data pointer, or an ERR_PTR.
 821 * The private data pointer should _only_ be dereferenced if the caller is the
 822 * owner of the data, or its content could vanish. This is mostly used to
 823 * confirm that a caller is the owner of a registered probe.
 824 */
 825void *marker_get_private_data(const char *name, marker_probe_func *probe,
 826                int num)
 827{
 828        struct hlist_head *head;
 829        struct hlist_node *node;
 830        struct marker_entry *e;
 831        size_t name_len = strlen(name) + 1;
 832        u32 hash = jhash(name, name_len-1, 0);
 833        int i;
 834
 835        head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
 836        hlist_for_each_entry(e, node, head, hlist) {
 837                if (!strcmp(name, e->name)) {
 838                        if (!e->ptype) {
 839                                if (num == 0 && e->single.func == probe)
 840                                        return e->single.probe_private;
 841                                else
 842                                        break;
 843                        } else {
 844                                struct marker_probe_closure *closure;
 845                                int match = 0;
 846                                closure = e->multi;
 847                                for (i = 0; closure[i].func; i++) {
 848                                        if (closure[i].func != probe)
 849                                                continue;
 850                                        if (match++ == num)
 851                                                return closure[i].probe_private;
 852                                }
 853                        }
 854                }
 855        }
 856        return ERR_PTR(-ENOENT);
 857}
 858EXPORT_SYMBOL_GPL(marker_get_private_data);
 859
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