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Diffstat (limited to 'src/kernel/tests/include/tst_fuzzy_sync.h')
| -rw-r--r-- | src/kernel/tests/include/tst_fuzzy_sync.h | 776 |
1 files changed, 776 insertions, 0 deletions
diff --git a/src/kernel/tests/include/tst_fuzzy_sync.h b/src/kernel/tests/include/tst_fuzzy_sync.h new file mode 100644 index 0000000..4141f5c --- /dev/null +++ b/src/kernel/tests/include/tst_fuzzy_sync.h @@ -0,0 +1,776 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* + * Copyright (c) 2017-2018 Richard Palethorpe <rpalethorpe@suse.com> + */ +/** + * @file tst_fuzzy_sync.h + * Fuzzy Synchronisation - abbreviated to fzsync + * + * This library is intended to help reproduce race conditions by synchronising + * two threads at a given place by marking the range a race may occur + * in. Because the exact place where any race occurs is within the kernel, + * and therefore impossible to mark accurately, the library may add randomised + * delays to either thread in order to help find the exact race timing. + * + * Currently only two way races are explicitly supported, that is races + * involving two threads or processes. We refer to the main test thread as + * thread A and the child thread as thread B. + * + * In each thread you need a simple while- or for-loop which the tst_fzsync_* + * functions are called in. In the simplest case thread A will look something + * like: + * + * tst_fzsync_pair_reset(&pair, run_thread_b); + * while (tst_fzsync_run_a(&pair)) { + * // Perform some setup which must happen before the race + * tst_fzsync_start_race_a(&pair); + * // Do some dodgy syscall + * tst_fzsync_end_race_a(&pair); + * } + * + * Then in thread B (run_thread_b): + * + * while (tst_fzsync_run_b(&pair)) { + * tst_fzsync_start_race_b(&pair); + * // Do something which can race with the dodgy syscall in A + * tst_fzsync_end_race_b(&pair) + * } + * + * The calls to tst_fzsync_start/end_race and tst_fzsync_run_a/b block (at + * least) until both threads have enter them. These functions can only be + * called once for each iteration, but further synchronisation points can be + * added by calling tst_fzsync_wait_a() and tst_fzsync_wait_b() in each + * thread. + * + * The execution of the loops in threads A and B are bounded by both iteration + * count and time. A slow machine is likely to be limited by time and a fast + * one by iteration count. The user can use the -i parameter to run the test + * multiple times or LTP_TIMEOUT_MUL to give the test more time. + * + * It is possible to use the library just for tst_fzsync_pair_wait() to get a + * basic spin wait. However if you are actually testing a race condition then + * it is recommended to use tst_fzsync_start_race_a/b even if the + * randomisation is not needed. It provides some semantic information which + * may be useful in the future. + * + * For a usage example see testcases/cve/cve-2016-7117.c or just run + * 'git grep tst_fuzzy_sync.h' + * + * @sa tst_fzsync_pair + */ + +#include <sys/time.h> +#include <time.h> +#include <math.h> +#include <stdlib.h> +#include <pthread.h> +#include "tst_atomic.h" +#include "tst_timer.h" +#include "tst_safe_pthread.h" + +#ifndef TST_FUZZY_SYNC_H__ +#define TST_FUZZY_SYNC_H__ + +/* how much of exec time is sampling allowed to take */ +#define SAMPLING_SLICE 0.5f + +/** Some statistics for a variable */ +struct tst_fzsync_stat { + float avg; + float avg_dev; + float dev_ratio; +}; + +/** + * The state of a two way synchronisation or race. + * + * This contains all the necessary state for approximately synchronising two + * sections of code in different threads. + * + * Some of the fields can be configured before calling + * tst_fzsync_pair_reset(), however this is mainly for debugging purposes. If + * a test requires one of the parameters to be modified, we should consider + * finding a way of automatically selecting an appropriate value at runtime. + * + * Internal fields should only be accessed by library functions. + */ +struct tst_fzsync_pair { + /** + * The rate at which old diff samples are forgotten + * + * Defaults to 0.25. + */ + float avg_alpha; + /** Internal; Thread A start time */ + struct timespec a_start; + /** Internal; Thread B start time */ + struct timespec b_start; + /** Internal; Thread A end time */ + struct timespec a_end; + /** Internal; Thread B end time */ + struct timespec b_end; + /** Internal; Avg. difference between a_start and b_start */ + struct tst_fzsync_stat diff_ss; + /** Internal; Avg. difference between a_start and a_end */ + struct tst_fzsync_stat diff_sa; + /** Internal; Avg. difference between b_start and b_end */ + struct tst_fzsync_stat diff_sb; + /** Internal; Avg. difference between a_end and b_end */ + struct tst_fzsync_stat diff_ab; + /** Internal; Number of spins while waiting for the slower thread */ + int spins; + struct tst_fzsync_stat spins_avg; + /** + * Internal; Number of spins to use in the delay. + * + * A negative value delays thread A and a positive delays thread B. + */ + int delay; + int delay_bias; + /** + * Internal; The number of samples left or the sampling state. + * + * A positive value is the number of remaining mandatory + * samples. Zero or a negative indicate some other state. + */ + int sampling; + /** + * The Minimum number of statistical samples which must be collected. + * + * The minimum number of iterations which must be performed before a + * random delay can be calculated. Defaults to 1024. + */ + int min_samples; + /** + * The maximum allowed proportional average deviation. + * + * A value in the range (0, 1) which gives the maximum average + * deviation which must be attained before random delays can be + * calculated. + * + * It is a ratio of (average_deviation / total_time). The default is + * 0.1, so this allows an average deviation of at most 10%. + */ + float max_dev_ratio; + + /** Internal; Atomic counter used by fzsync_pair_wait() */ + int a_cntr; + /** Internal; Atomic counter used by fzsync_pair_wait() */ + int b_cntr; + /** Internal; Used by tst_fzsync_pair_exit() and fzsync_pair_wait() */ + int exit; + /** + * The maximum desired execution time as a proportion of the timeout + * + * A value x so that 0 < x < 1 which decides how long the test should + * be run for (assuming the loop limit is not exceeded first). + * + * Defaults to 0.5 (~150 seconds with default timeout). + */ + float exec_time_p; + /** Internal; The test time remaining on tst_fzsync_pair_reset() */ + float exec_time_start; + /** + * The maximum number of iterations to execute during the test + * + * Defaults to a large number, but not too large. + */ + int exec_loops; + /** Internal; The current loop index */ + int exec_loop; + /** Internal; The second thread or 0 */ + pthread_t thread_b; +}; + +#define CHK(param, low, hi, def) do { \ + pair->param = (pair->param ? pair->param : def); \ + if (pair->param < low) \ + tst_brk(TBROK, #param " is less than the lower bound " #low); \ + if (pair->param > hi) \ + tst_brk(TBROK, #param " is more than the upper bound " #hi); \ + } while (0) +/** + * Ensures that any Fuzzy Sync parameters are properly set + * + * @relates tst_fzsync_pair + * + * Usually called from the setup function, it sets default parameter values or + * validates any existing non-defaults. + * + * @sa tst_fzsync_pair_reset() + */ +static void tst_fzsync_pair_init(struct tst_fzsync_pair *pair) +{ + CHK(avg_alpha, 0, 1, 0.25); + CHK(min_samples, 20, INT_MAX, 1024); + CHK(max_dev_ratio, 0, 1, 0.1); + CHK(exec_time_p, 0, 1, 0.5); + CHK(exec_loops, 20, INT_MAX, 3000000); +} +#undef CHK + +/** + * Exit and join thread B if necessary. + * + * @relates tst_fzsync_pair + * + * Call this from your cleanup function. + */ +static void tst_fzsync_pair_cleanup(struct tst_fzsync_pair *pair) +{ + if (pair->thread_b) { + /* Revoke thread B if parent hits accidental break */ + if (!pair->exit) { + tst_atomic_store(1, &pair->exit); + usleep(100000); + pthread_cancel(pair->thread_b); + } + SAFE_PTHREAD_JOIN(pair->thread_b, NULL); + pair->thread_b = 0; + } +} + +/** To store the run_b pointer and pass to tst_fzsync_thread_wrapper */ +struct tst_fzsync_run_thread { + void *(*func)(void *); + void *arg; +}; + +/** + * Wrap run_b for tst_fzsync_pair_reset to enable pthread cancel + * at the start of the thread B. + */ +static void *tst_fzsync_thread_wrapper(void *run_thread) +{ + struct tst_fzsync_run_thread t = *(struct tst_fzsync_run_thread *)run_thread; + + pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL); + pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL); + return t.func(t.arg); +} + +/** + * Zero some stat fields + * + * @relates tst_fzsync_stat + */ +static void tst_init_stat(struct tst_fzsync_stat *s) +{ + s->avg = 0; + s->avg_dev = 0; +} + +/** + * Reset or initialise fzsync. + * + * @relates tst_fzsync_pair + * @param pair The state structure initialised with TST_FZSYNC_PAIR_INIT. + * @param run_b The function defining thread B or NULL. + * + * Call this from your main test function (thread A), just before entering the + * main loop. It will (re)set any variables needed by fzsync and (re)start + * thread B using the function provided. + * + * If you need to use fork or clone to start the second thread/process then + * you can pass NULL to run_b and handle starting and stopping thread B + * yourself. You may need to place tst_fzsync_pair in some shared memory as + * well. + * + * @sa tst_fzsync_pair_init() + */ +static void tst_fzsync_pair_reset(struct tst_fzsync_pair *pair, + void *(*run_b)(void *)) +{ + tst_fzsync_pair_cleanup(pair); + + tst_init_stat(&pair->diff_ss); + tst_init_stat(&pair->diff_sa); + tst_init_stat(&pair->diff_sb); + tst_init_stat(&pair->diff_ab); + tst_init_stat(&pair->spins_avg); + pair->delay = 0; + pair->sampling = pair->min_samples; + + pair->exec_loop = 0; + + pair->a_cntr = 0; + pair->b_cntr = 0; + pair->exit = 0; + if (run_b) { + static struct tst_fzsync_run_thread wrap_run_b; + + wrap_run_b.func = run_b; + wrap_run_b.arg = NULL; + SAFE_PTHREAD_CREATE(&pair->thread_b, 0, tst_fzsync_thread_wrapper, &wrap_run_b); + } + + pair->exec_time_start = (float)tst_timeout_remaining(); +} + +/** + * Print stat + * + * @relates tst_fzsync_stat + */ +static inline void tst_fzsync_stat_info(struct tst_fzsync_stat stat, + char *unit, char *name) +{ + tst_res(TINFO, + "%1$-17s: { avg = %3$5.0f%2$s, avg_dev = %4$5.0f%2$s, dev_ratio = %5$.2f }", + name, unit, stat.avg, stat.avg_dev, stat.dev_ratio); +} + +/** + * Print some synchronisation statistics + * + * @relates tst_fzsync_pair + */ +static void tst_fzsync_pair_info(struct tst_fzsync_pair *pair) +{ + tst_res(TINFO, "loop = %d, delay_bias = %d", + pair->exec_loop, pair->delay_bias); + tst_fzsync_stat_info(pair->diff_ss, "ns", "start_a - start_b"); + tst_fzsync_stat_info(pair->diff_sa, "ns", "end_a - start_a"); + tst_fzsync_stat_info(pair->diff_sb, "ns", "end_b - start_b"); + tst_fzsync_stat_info(pair->diff_ab, "ns", "end_a - end_b"); + tst_fzsync_stat_info(pair->spins_avg, " ", "spins"); +} + +/** Wraps clock_gettime */ +static inline void tst_fzsync_time(struct timespec *t) +{ +#ifdef CLOCK_MONOTONIC_RAW + clock_gettime(CLOCK_MONOTONIC_RAW, t); +#else + clock_gettime(CLOCK_MONOTONIC, t); +#endif +} + +/** + * Exponential moving average + * + * @param alpha The preference for recent samples over old ones. + * @param sample The current sample + * @param prev_avg The average of the all the previous samples + * + * @return The average including the current sample. + */ +static inline float tst_exp_moving_avg(float alpha, + float sample, + float prev_avg) +{ + return alpha * sample + (1.0 - alpha) * prev_avg; +} + +/** + * Update a stat with a new sample + * + * @relates tst_fzsync_stat + */ +static inline void tst_upd_stat(struct tst_fzsync_stat *s, + float alpha, + float sample) +{ + s->avg = tst_exp_moving_avg(alpha, sample, s->avg); + s->avg_dev = tst_exp_moving_avg(alpha, + fabs(s->avg - sample), s->avg_dev); + s->dev_ratio = fabs(s->avg ? s->avg_dev / s->avg : 0); +} + +/** + * Update a stat with a new diff sample + * + * @relates tst_fzsync_stat + */ +static inline void tst_upd_diff_stat(struct tst_fzsync_stat *s, + float alpha, + struct timespec t1, + struct timespec t2) +{ + tst_upd_stat(s, alpha, tst_timespec_diff_ns(t1, t2)); +} + +/** + * Calculate various statistics and the delay + * + * This function helps create the fuzz in fuzzy sync. Imagine we have the + * following timelines in threads A and B: + * + * start_race_a + * ^ end_race_a (a) + * | ^ + * | | + * - --+------------------------+-- - - + * | Syscall A | Thread A + * - --+------------------------+-- - - + * - --+----------------+-------+-- - - + * | Syscall B | spin | Thread B + * - --+----------------+-------+-- - - + * | | + * ^ ^ + * start_race_b end_race_b + * + * Here we have synchronised the calls to syscall A and B with start_race_{a, + * b} so that they happen at approximately the same time in threads A and + * B. If the race condition occurs during the entry code for these two + * functions then we will quickly hit it. If it occurs during the exit code of + * B and mid way through A, then we will quickly hit it. + * + * However if the exit paths of A and B need to be aligned and (end_race_a - + * end_race_b) is large relative to the variation in call times, the + * probability of hitting the race condition is close to zero. To solve this + * scenario (and others) a randomised delay is introduced before the syscalls + * in A and B. Given enough time the following should happen where the exit + * paths are now synchronised: + * + * start_race_a + * ^ end_race_a (a) + * | ^ + * | | + * - --+------------------------+-- - - + * | Syscall A | Thread A + * - --+------------------------+-- - - + * - --+-------+----------------+-- - - + * | delay | Syscall B | Thread B + * - --+-------+----------------+-- - - + * | | + * ^ ^ + * start_race_b end_race_b + * + * The delay is not introduced immediately and the delay range is only + * calculated once the average relative deviation has dropped below some + * percentage of the total time. + * + * The delay range is chosen so that any point in Syscall A could be + * synchronised with any point in Syscall B using a value from the + * range. Because the delay range may be too large for a linear search, we use + * an evenly distributed random function to pick a value from it. + * + * The delay range goes from positive to negative. A negative delay will delay + * thread A and a positive one will delay thread B. The range is bounded by + * the point where the entry code to Syscall A is synchronised with the exit + * to Syscall B and the entry code to Syscall B is synchronised with the exit + * of A. + * + * In order to calculate the lower bound (the max delay of A) we can simply + * negate the execution time of Syscall B and convert it to a spin count. For + * the upper bound (the max delay of B), we just take the execution time of A + * and convert it to a spin count. + * + * In order to calculate spin count we need to know approximately how long a + * spin takes and divide the delay time with it. We find this by first + * counting how many spins one thread spends waiting for the other during + * end_race[1]. We also know when each syscall exits so we can take the + * difference between the exit times and divide it with the number of spins + * spent waiting. + * + * All the times and counts we use in the calculation are averaged over a + * variable number of iterations. There is an initial sampling period where we + * simply collect time and count samples then calculate their averages. When a + * minimum number of samples have been collected, and if the average deviation + * is below some proportion of the average sample magnitude, then the sampling + * period is ended. On all further iterations a random delay is calculated and + * applied, but the averages are not updated. + * + * [1] This assumes there is always a significant difference. The algorithm + * may fail to introduce a delay (when one is needed) in situations where + * Syscall A and B finish at approximately the same time. + * + * @relates tst_fzsync_pair + */ +static void tst_fzsync_pair_update(struct tst_fzsync_pair *pair) +{ + float alpha = pair->avg_alpha; + float per_spin_time, time_delay; + float max_dev = pair->max_dev_ratio; + int over_max_dev; + + pair->delay = pair->delay_bias; + + over_max_dev = pair->diff_ss.dev_ratio > max_dev + || pair->diff_sa.dev_ratio > max_dev + || pair->diff_sb.dev_ratio > max_dev + || pair->diff_ab.dev_ratio > max_dev + || pair->spins_avg.dev_ratio > max_dev; + + if (pair->sampling > 0 || over_max_dev) { + tst_upd_diff_stat(&pair->diff_ss, alpha, + pair->a_start, pair->b_start); + tst_upd_diff_stat(&pair->diff_sa, alpha, + pair->a_end, pair->a_start); + tst_upd_diff_stat(&pair->diff_sb, alpha, + pair->b_end, pair->b_start); + tst_upd_diff_stat(&pair->diff_ab, alpha, + pair->a_end, pair->b_end); + tst_upd_stat(&pair->spins_avg, alpha, pair->spins); + if (pair->sampling > 0 && --pair->sampling == 0) { + tst_res(TINFO, "Minimum sampling period ended"); + tst_fzsync_pair_info(pair); + } + } else if (fabsf(pair->diff_ab.avg) >= 1) { + per_spin_time = fabsf(pair->diff_ab.avg) / MAX(pair->spins_avg.avg, 1.0f); + time_delay = drand48() * (pair->diff_sa.avg + pair->diff_sb.avg) + - pair->diff_sb.avg; + pair->delay += (int)(1.1 * time_delay / per_spin_time); + + if (!pair->sampling) { + tst_res(TINFO, + "Reached deviation ratios < %.2f, introducing randomness", + pair->max_dev_ratio); + tst_res(TINFO, "Delay range is [-%d, %d]", + (int)(pair->diff_sb.avg / per_spin_time) + pair->delay_bias, + (int)(pair->diff_sa.avg / per_spin_time) - pair->delay_bias); + tst_fzsync_pair_info(pair); + pair->sampling = -1; + } + } else if (!pair->sampling) { + tst_res(TWARN, "Can't calculate random delay"); + tst_fzsync_pair_info(pair); + pair->sampling = -1; + } + + pair->spins = 0; +} + +/** + * Wait for the other thread + * + * @relates tst_fzsync_pair + * @param our_cntr The counter for the thread we are on + * @param other_cntr The counter for the thread we are synchronising with + * @param spins A pointer to the spin counter or NULL + * + * Used by tst_fzsync_pair_wait_a(), tst_fzsync_pair_wait_b(), + * tst_fzsync_start_race_a(), etc. If the calling thread is ahead of the other + * thread, then it will spin wait. Unlike pthread_barrier_wait it will never + * use futex and can count the number of spins spent waiting. + * + * @return A non-zero value if the thread should continue otherwise the + * calling thread should exit. + */ +static inline void tst_fzsync_pair_wait(int *our_cntr, + int *other_cntr, + int *spins) +{ + if (tst_atomic_inc(other_cntr) == INT_MAX) { + /* + * We are about to break the invariant that the thread with + * the lowest count is in front of the other. So we must wait + * here to ensure the other thread has at least reached the + * line above before doing that. If we are in rear position + * then our counter may already have been set to zero. + */ + while (tst_atomic_load(our_cntr) > 0 + && tst_atomic_load(our_cntr) < INT_MAX) { + if (spins) + (*spins)++; + } + + tst_atomic_store(0, other_cntr); + /* + * Once both counters have been set to zero the invariant + * is restored and we can continue. + */ + while (tst_atomic_load(our_cntr) > 1) + ; + } else { + /* + * If our counter is less than the other thread's we are ahead + * of it and need to wait. + */ + while (tst_atomic_load(our_cntr) < tst_atomic_load(other_cntr)) { + if (spins) + (*spins)++; + } + } +} + +/** + * Wait in thread A + * + * @relates tst_fzsync_pair + * @sa tst_fzsync_pair_wait + */ +static inline void tst_fzsync_wait_a(struct tst_fzsync_pair *pair) +{ + tst_fzsync_pair_wait(&pair->a_cntr, &pair->b_cntr, NULL); +} + +/** + * Wait in thread B + * + * @relates tst_fzsync_pair + * @sa tst_fzsync_pair_wait + */ +static inline void tst_fzsync_wait_b(struct tst_fzsync_pair *pair) +{ + tst_fzsync_pair_wait(&pair->b_cntr, &pair->a_cntr, NULL); +} + +/** + * Decide whether to continue running thread A + * + * @relates tst_fzsync_pair + * + * Checks some values and decides whether it is time to break the loop of + * thread A. + * + * @return True to continue and false to break. + * @sa tst_fzsync_run_a + */ +static inline int tst_fzsync_run_a(struct tst_fzsync_pair *pair) +{ + int exit = 0; + float rem_p = 1 - tst_timeout_remaining() / pair->exec_time_start; + + if ((pair->exec_time_p * SAMPLING_SLICE < rem_p) + && (pair->sampling > 0)) { + tst_res(TINFO, "Stopped sampling at %d (out of %d) samples, " + "sampling time reached 50%% of the total time limit", + pair->exec_loop, pair->min_samples); + pair->sampling = 0; + tst_fzsync_pair_info(pair); + } + + if (pair->exec_time_p < rem_p) { + tst_res(TINFO, + "Exceeded execution time, requesting exit"); + exit = 1; + } + + if (++pair->exec_loop > pair->exec_loops) { + tst_res(TINFO, + "Exceeded execution loops, requesting exit"); + exit = 1; + } + + tst_atomic_store(exit, &pair->exit); + tst_fzsync_wait_a(pair); + + if (exit) { + tst_fzsync_pair_cleanup(pair); + return 0; + } + + return 1; +} + +/** + * Decide whether to continue running thread B + * + * @relates tst_fzsync_pair + * @sa tst_fzsync_run_a + */ +static inline int tst_fzsync_run_b(struct tst_fzsync_pair *pair) +{ + tst_fzsync_wait_b(pair); + return !tst_atomic_load(&pair->exit); +} + +/** + * Marks the start of a race region in thread A + * + * @relates tst_fzsync_pair + * + * This should be placed just before performing whatever action can cause a + * race condition. Usually it is placed just before a syscall and + * tst_fzsync_end_race_a() is placed just afterwards. + * + * A corresponding call to tst_fzsync_start_race_b() should be made in thread + * B. + * + * @return A non-zero value if the calling thread should continue to loop. If + * it returns zero then tst_fzsync_exit() has been called and you must exit + * the thread. + * + * @sa tst_fzsync_pair_update + */ +static inline void tst_fzsync_start_race_a(struct tst_fzsync_pair *pair) +{ + volatile int delay; + + tst_fzsync_pair_update(pair); + + tst_fzsync_wait_a(pair); + + delay = pair->delay; + while (delay < 0) + delay++; + + tst_fzsync_time(&pair->a_start); +} + +/** + * Marks the end of a race region in thread A + * + * @relates tst_fzsync_pair + * @sa tst_fzsync_start_race_a + */ +static inline void tst_fzsync_end_race_a(struct tst_fzsync_pair *pair) +{ + tst_fzsync_time(&pair->a_end); + tst_fzsync_pair_wait(&pair->a_cntr, &pair->b_cntr, &pair->spins); +} + +/** + * Marks the start of a race region in thread B + * + * @relates tst_fzsync_pair + * @sa tst_fzsync_start_race_a + */ +static inline void tst_fzsync_start_race_b(struct tst_fzsync_pair *pair) +{ + volatile int delay; + + tst_fzsync_wait_b(pair); + + delay = pair->delay; + while (delay > 0) + delay--; + + tst_fzsync_time(&pair->b_start); +} + +/** + * Marks the end of a race region in thread B + * + * @relates tst_fzsync_pair + * @sa tst_fzsync_start_race_a + */ +static inline void tst_fzsync_end_race_b(struct tst_fzsync_pair *pair) +{ + tst_fzsync_time(&pair->b_end); + tst_fzsync_pair_wait(&pair->b_cntr, &pair->a_cntr, &pair->spins); +} + +/** + * Add some amount to the delay bias + * + * @relates tst_fzsync_pair + * @param change The amount to add, can be negative + * + * A positive change delays thread B and a negative one delays thread + * A. + * + * It is intended to be used in tests where the time taken by syscall A and/or + * B are significantly affected by their chronological order. To the extent + * that the delay range will not include the correct values if too many of the + * initial samples are taken when the syscalls (or operations within the + * syscalls) happen in the wrong order. + * + * An example of this is cve/cve-2016-7117.c where a call to close() is racing + * with a call to recvmmsg(). If close() happens before recvmmsg() has chance + * to check if the file descriptor is open then recvmmsg() completes very + * quickly. If the call to close() happens once recvmmsg() has already checked + * the descriptor it takes much longer. The sample where recvmmsg() completes + * quickly is essentially invalid for our purposes. The test uses the simple + * heuristic of whether recvmmsg() returns EBADF, to decide if it should call + * tst_fzsync_pair_add_bias() to further delay syscall B. + */ +static inline void tst_fzsync_pair_add_bias(struct tst_fzsync_pair *pair, int change) +{ + if (pair->sampling > 0) + pair->delay_bias += change; +} + +#endif /* TST_FUZZY_SYNC_H__ */ |