From: Suren Baghdasaryan Date: Sat, 19 Jul 2025 18:28:49 +0000 (-0700) Subject: selftests/proc: add /proc/pid/maps tearing from vma split test X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=beb69e81724634063b9dbae4bc79e2e011fdeeb1;p=thirdparty%2Fkernel%2Flinux.git selftests/proc: add /proc/pid/maps tearing from vma split test Patch series "use per-vma locks for /proc/pid/maps reads", v8. Reading /proc/pid/maps requires read-locking mmap_lock which prevents any other task from concurrently modifying the address space. This guarantees coherent reporting of virtual address ranges, however it can block important updates from happening. Oftentimes /proc/pid/maps readers are low priority monitoring tasks and them blocking high priority tasks results in priority inversion. Locking the entire address space is required to present fully coherent picture of the address space, however even current implementation does not strictly guarantee that by outputting vmas in page-size chunks and dropping mmap_lock in between each chunk. Address space modifications are possible while mmap_lock is dropped and userspace reading the content is expected to deal with possible concurrent address space modifications. Considering these relaxed rules, holding mmap_lock is not strictly needed as long as we can guarantee that a concurrently modified vma is reported either in its original form or after it was modified. This patchset switches from holding mmap_lock while reading /proc/pid/maps to taking per-vma locks as we walk the vma tree. This reduces the contention with tasks modifying the address space because they would have to contend for the same vma as opposed to the entire address space. Previous version of this patchset [1] tried to perform /proc/pid/maps reading under RCU, however its implementation is quite complex and the results are worse than the new version because it still relied on mmap_lock speculation which retries if any part of the address space gets modified. New implementaion is both simpler and results in less contention. Note that similar approach would not work for /proc/pid/smaps reading as it also walks the page table and that's not RCU-safe. Paul McKenney's designed a test [2] to measure mmap/munmap latencies while concurrently reading /proc/pid/maps. The test has a pair of processes scanning /proc/PID/maps, and another process unmapping and remapping 4K pages from a 128MB range of anonymous memory. At the end of each 10 second run, the latency of each mmap() or munmap() operation is measured, and for each run the maximum and mean latency is printed. The map/unmap process is started first, its PID is passed to the scanners, and then the map/unmap process waits until both scanners are running before starting its timed test. The scanners keep scanning until the specified /proc/PID/maps file disappears. The latest results from Paul: Stock mm-unstable, all of the runs had maximum latencies in excess of 0.5 milliseconds, and with 80% of the runs' latencies exceeding a full millisecond, and ranging up beyond 4 full milliseconds. In contrast, 99% of the runs with this patch series applied had maximum latencies of less than 0.5 milliseconds, with the single outlier at only 0.608 milliseconds. From a median-performance (as opposed to maximum-latency) viewpoint, this patch series also looks good, with stock mm weighing in at 11 microseconds and patch series at 6 microseconds, better than a 2x improvement. Before the change: ./run-proc-vs-map.sh --nsamples 100 --rawdata -- --busyduration 2 0.011 0.008 0.521 0.011 0.008 0.552 0.011 0.008 0.590 0.011 0.008 0.660 ... 0.011 0.015 2.987 0.011 0.015 3.038 0.011 0.016 3.431 0.011 0.016 4.707 After the change: ./run-proc-vs-map.sh --nsamples 100 --rawdata -- --busyduration 2 0.006 0.005 0.026 0.006 0.005 0.029 0.006 0.005 0.034 0.006 0.005 0.035 ... 0.006 0.006 0.421 0.006 0.006 0.423 0.006 0.006 0.439 0.006 0.006 0.608 The patchset also adds a number of tests to check for /proc/pid/maps data coherency. They are designed to detect any unexpected data tearing while performing some common address space modifications (vma split, resize and remap). Even before these changes, reading /proc/pid/maps might have inconsistent data because the file is read page-by-page with mmap_lock being dropped between the pages. An example of user-visible inconsistency can be that the same vma is printed twice: once before it was modified and then after the modifications. For example if vma was extended, it might be found and reported twice. What is not expected is to see a gap where there should have been a vma both before and after modification. This patchset increases the chances of such tearing, therefore it's even more important now to test for unexpected inconsistencies. In [3] Lorenzo identified the following possible vma merging/splitting scenarios: Merges with changes to existing vmas: 1 Merge both - mapping a vma over another one and between two vmas which can be merged after this replacement; 2. Merge left full - mapping a vma at the end of an existing one and completely over its right neighbor; 3. Merge left partial - mapping a vma at the end of an existing one and partially over its right neighbor; 4. Merge right full - mapping a vma before the start of an existing one and completely over its left neighbor; 5. Merge right partial - mapping a vma before the start of an existing one and partially over its left neighbor; Merges without changes to existing vmas: 6. Merge both - mapping a vma into a gap between two vmas which can be merged after the insertion; 7. Merge left - mapping a vma at the end of an existing one; 8. Merge right - mapping a vma before the start end of an existing one; Splits 9. Split with new vma at the lower address; 10. Split with new vma at the higher address; If such merges or splits happen concurrently with the /proc/maps reading we might report a vma twice, once before the modification and once after it is modified: Case 1 might report overwritten and previous vma along with the final merged vma; Case 2 might report previous and the final merged vma; Case 3 might cause us to retry once we detect the temporary gap caused by shrinking of the right neighbor; Case 4 might report overritten and the final merged vma; Case 5 might cause us to retry once we detect the temporary gap caused by shrinking of the left neighbor; Case 6 might report previous vma and the gap along with the final marged vma; Case 7 might report previous and the final merged vma; Case 8 might report the original gap and the final merged vma covering the gap; Case 9 might cause us to retry once we detect the temporary gap caused by shrinking of the original vma at the vma start; Case 10 might cause us to retry once we detect the temporary gap caused by shrinking of the original vma at the vma end; In all these cases the retry mechanism prevents us from reporting possible temporary gaps. [1] https://lore.kernel.org/all/20250418174959.1431962-1-surenb@google.com/ [2] https://github.com/paulmckrcu/proc-mmap_sem-test [3] https://lore.kernel.org/all/e1863f40-39ab-4e5b-984a-c48765ffde1c@lucifer.local/ The /proc/pid/maps file is generated page by page, with the mmap_lock released between pages. This can lead to inconsistent reads if the underlying vmas are concurrently modified. For instance, if a vma split or merge occurs at a page boundary while /proc/pid/maps is being read, the same vma might be seen twice: once before and once after the change. This duplication is considered acceptable for userspace handling. However, observing a "hole" where a vma should be (e.g., due to a vma being replaced and the space temporarily being empty) is unacceptable. Implement a test that: 1. Forks a child process which continuously modifies its address space, specifically targeting a vma at the boundary between two pages. 2. The parent process repeatedly reads the child's /proc/pid/maps. 3. The parent process checks the last vma of the first page and the first vma of the second page for consistency, looking for the effects of vma splits or merges. The test duration is configurable via DURATION environment variable expressed in seconds. The default test duration is 5 seconds. Example Command: DURATION=10 ./proc-maps-race Link: https://lore.kernel.org/all/20250418174959.1431962-1-surenb@google.com/ [1] Link: https://github.com/paulmckrcu/proc-mmap_sem-test [2] Link: https://lore.kernel.org/all/e1863f40-39ab-4e5b-984a-c48765ffde1c@lucifer.local/ [3] Link: https://lkml.kernel.org/r/20250719182854.3166724-1-surenb@google.com Link: https://lkml.kernel.org/r/20250719182854.3166724-2-surenb@google.com Signed-off-by: Suren Baghdasaryan Cc: Alexey Dobriyan Cc: Andrii Nakryiko Cc: Christian Brauner Cc: Christophe Leroy Cc: David Hildenbrand Cc: Jann Horn Cc: Jeongjun Park Cc: Johannes Weiner Cc: Josef Bacik Cc: Kalesh Singh Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Oscar Salvador Cc: "Paul E . McKenney" Cc: Peter Xu Cc: Ryan Roberts Cc: Shuah Khan Cc: Thomas Weißschuh Cc: T.J. Mercier Cc: Vlastimil Babka Cc: Ye Bin Signed-off-by: Andrew Morton --- diff --git a/tools/testing/selftests/proc/.gitignore b/tools/testing/selftests/proc/.gitignore index 973968f45bba0..19bb333e2485f 100644 --- a/tools/testing/selftests/proc/.gitignore +++ b/tools/testing/selftests/proc/.gitignore @@ -5,6 +5,7 @@ /proc-2-is-kthread /proc-fsconfig-hidepid /proc-loadavg-001 +/proc-maps-race /proc-multiple-procfs /proc-empty-vm /proc-pid-vm diff --git a/tools/testing/selftests/proc/Makefile b/tools/testing/selftests/proc/Makefile index b12921b9794b0..50aba102201a9 100644 --- a/tools/testing/selftests/proc/Makefile +++ b/tools/testing/selftests/proc/Makefile @@ -9,6 +9,7 @@ TEST_GEN_PROGS += fd-002-posix-eq TEST_GEN_PROGS += fd-003-kthread TEST_GEN_PROGS += proc-2-is-kthread TEST_GEN_PROGS += proc-loadavg-001 +TEST_GEN_PROGS += proc-maps-race TEST_GEN_PROGS += proc-empty-vm TEST_GEN_PROGS += proc-pid-vm TEST_GEN_PROGS += proc-self-map-files-001 diff --git a/tools/testing/selftests/proc/proc-maps-race.c b/tools/testing/selftests/proc/proc-maps-race.c new file mode 100644 index 0000000000000..5b28dda08b7da --- /dev/null +++ b/tools/testing/selftests/proc/proc-maps-race.c @@ -0,0 +1,447 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright 2022 Google LLC. + * Author: Suren Baghdasaryan + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ +/* + * Fork a child that concurrently modifies address space while the main + * process is reading /proc/$PID/maps and verifying the results. Address + * space modifications include: + * VMA splitting and merging + * + */ +#define _GNU_SOURCE +#include "../kselftest_harness.h" +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* /proc/pid/maps parsing routines */ +struct page_content { + char *data; + ssize_t size; +}; + +#define LINE_MAX_SIZE 256 + +struct line_content { + char text[LINE_MAX_SIZE]; + unsigned long start_addr; + unsigned long end_addr; +}; + +enum test_state { + INIT, + CHILD_READY, + PARENT_READY, + SETUP_READY, + SETUP_MODIFY_MAPS, + SETUP_MAPS_MODIFIED, + SETUP_RESTORE_MAPS, + SETUP_MAPS_RESTORED, + TEST_READY, + TEST_DONE, +}; + +struct vma_modifier_info; + +FIXTURE(proc_maps_race) +{ + struct vma_modifier_info *mod_info; + struct page_content page1; + struct page_content page2; + struct line_content last_line; + struct line_content first_line; + unsigned long duration_sec; + int shared_mem_size; + int page_size; + int vma_count; + int maps_fd; + pid_t pid; +}; + +typedef bool (*vma_modifier_op)(FIXTURE_DATA(proc_maps_race) *self); +typedef bool (*vma_mod_result_check_op)(struct line_content *mod_last_line, + struct line_content *mod_first_line, + struct line_content *restored_last_line, + struct line_content *restored_first_line); + +struct vma_modifier_info { + int vma_count; + void *addr; + int prot; + void *next_addr; + vma_modifier_op vma_modify; + vma_modifier_op vma_restore; + vma_mod_result_check_op vma_mod_check; + pthread_mutex_t sync_lock; + pthread_cond_t sync_cond; + enum test_state curr_state; + bool exit; + void *child_mapped_addr[]; +}; + + +static bool read_two_pages(FIXTURE_DATA(proc_maps_race) *self) +{ + ssize_t bytes_read; + + if (lseek(self->maps_fd, 0, SEEK_SET) < 0) + return false; + + bytes_read = read(self->maps_fd, self->page1.data, self->page_size); + if (bytes_read <= 0) + return false; + + self->page1.size = bytes_read; + + bytes_read = read(self->maps_fd, self->page2.data, self->page_size); + if (bytes_read <= 0) + return false; + + self->page2.size = bytes_read; + + return true; +} + +static void copy_first_line(struct page_content *page, char *first_line) +{ + char *pos = strchr(page->data, '\n'); + + strncpy(first_line, page->data, pos - page->data); + first_line[pos - page->data] = '\0'; +} + +static void copy_last_line(struct page_content *page, char *last_line) +{ + /* Get the last line in the first page */ + const char *end = page->data + page->size - 1; + /* skip last newline */ + const char *pos = end - 1; + + /* search previous newline */ + while (pos[-1] != '\n') + pos--; + strncpy(last_line, pos, end - pos); + last_line[end - pos] = '\0'; +} + +/* Read the last line of the first page and the first line of the second page */ +static bool read_boundary_lines(FIXTURE_DATA(proc_maps_race) *self, + struct line_content *last_line, + struct line_content *first_line) +{ + if (!read_two_pages(self)) + return false; + + copy_last_line(&self->page1, last_line->text); + copy_first_line(&self->page2, first_line->text); + + return sscanf(last_line->text, "%lx-%lx", &last_line->start_addr, + &last_line->end_addr) == 2 && + sscanf(first_line->text, "%lx-%lx", &first_line->start_addr, + &first_line->end_addr) == 2; +} + +/* Thread synchronization routines */ +static void wait_for_state(struct vma_modifier_info *mod_info, enum test_state state) +{ + pthread_mutex_lock(&mod_info->sync_lock); + while (mod_info->curr_state != state) + pthread_cond_wait(&mod_info->sync_cond, &mod_info->sync_lock); + pthread_mutex_unlock(&mod_info->sync_lock); +} + +static void signal_state(struct vma_modifier_info *mod_info, enum test_state state) +{ + pthread_mutex_lock(&mod_info->sync_lock); + mod_info->curr_state = state; + pthread_cond_signal(&mod_info->sync_cond); + pthread_mutex_unlock(&mod_info->sync_lock); +} + +static void stop_vma_modifier(struct vma_modifier_info *mod_info) +{ + wait_for_state(mod_info, SETUP_READY); + mod_info->exit = true; + signal_state(mod_info, SETUP_MODIFY_MAPS); +} + +static bool capture_mod_pattern(FIXTURE_DATA(proc_maps_race) *self, + struct line_content *mod_last_line, + struct line_content *mod_first_line, + struct line_content *restored_last_line, + struct line_content *restored_first_line) +{ + signal_state(self->mod_info, SETUP_MODIFY_MAPS); + wait_for_state(self->mod_info, SETUP_MAPS_MODIFIED); + + /* Copy last line of the first page and first line of the last page */ + if (!read_boundary_lines(self, mod_last_line, mod_first_line)) + return false; + + signal_state(self->mod_info, SETUP_RESTORE_MAPS); + wait_for_state(self->mod_info, SETUP_MAPS_RESTORED); + + /* Copy last line of the first page and first line of the last page */ + if (!read_boundary_lines(self, restored_last_line, restored_first_line)) + return false; + + if (!self->mod_info->vma_mod_check(mod_last_line, mod_first_line, + restored_last_line, restored_first_line)) + return false; + + /* + * The content of these lines after modify+resore should be the same + * as the original. + */ + return strcmp(restored_last_line->text, self->last_line.text) == 0 && + strcmp(restored_first_line->text, self->first_line.text) == 0; +} + +static inline bool split_vma(FIXTURE_DATA(proc_maps_race) *self) +{ + return mmap(self->mod_info->addr, self->page_size, self->mod_info->prot | PROT_EXEC, + MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0) != MAP_FAILED; +} + +static inline bool merge_vma(FIXTURE_DATA(proc_maps_race) *self) +{ + return mmap(self->mod_info->addr, self->page_size, self->mod_info->prot, + MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0) != MAP_FAILED; +} + +static inline bool check_split_result(struct line_content *mod_last_line, + struct line_content *mod_first_line, + struct line_content *restored_last_line, + struct line_content *restored_first_line) +{ + /* Make sure vmas at the boundaries are changing */ + return strcmp(mod_last_line->text, restored_last_line->text) != 0 && + strcmp(mod_first_line->text, restored_first_line->text) != 0; +} + +FIXTURE_SETUP(proc_maps_race) +{ + const char *duration = getenv("DURATION"); + struct vma_modifier_info *mod_info; + pthread_mutexattr_t mutex_attr; + pthread_condattr_t cond_attr; + unsigned long duration_sec; + char fname[32]; + + self->page_size = (unsigned long)sysconf(_SC_PAGESIZE); + duration_sec = duration ? atol(duration) : 0; + self->duration_sec = duration_sec ? duration_sec : 5UL; + + /* + * Have to map enough vmas for /proc/pid/maps to contain more than one + * page worth of vmas. Assume at least 32 bytes per line in maps output + */ + self->vma_count = self->page_size / 32 + 1; + self->shared_mem_size = sizeof(struct vma_modifier_info) + self->vma_count * sizeof(void *); + + /* map shared memory for communication with the child process */ + self->mod_info = (struct vma_modifier_info *)mmap(NULL, self->shared_mem_size, + PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0); + ASSERT_NE(self->mod_info, MAP_FAILED); + mod_info = self->mod_info; + + /* Initialize shared members */ + pthread_mutexattr_init(&mutex_attr); + pthread_mutexattr_setpshared(&mutex_attr, PTHREAD_PROCESS_SHARED); + ASSERT_EQ(pthread_mutex_init(&mod_info->sync_lock, &mutex_attr), 0); + pthread_condattr_init(&cond_attr); + pthread_condattr_setpshared(&cond_attr, PTHREAD_PROCESS_SHARED); + ASSERT_EQ(pthread_cond_init(&mod_info->sync_cond, &cond_attr), 0); + mod_info->vma_count = self->vma_count; + mod_info->curr_state = INIT; + mod_info->exit = false; + + self->pid = fork(); + if (!self->pid) { + /* Child process modifying the address space */ + int prot = PROT_READ | PROT_WRITE; + int i; + + for (i = 0; i < mod_info->vma_count; i++) { + mod_info->child_mapped_addr[i] = mmap(NULL, self->page_size * 3, prot, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + ASSERT_NE(mod_info->child_mapped_addr[i], MAP_FAILED); + /* change protection in adjacent maps to prevent merging */ + prot ^= PROT_WRITE; + } + signal_state(mod_info, CHILD_READY); + wait_for_state(mod_info, PARENT_READY); + while (true) { + signal_state(mod_info, SETUP_READY); + wait_for_state(mod_info, SETUP_MODIFY_MAPS); + if (mod_info->exit) + break; + + ASSERT_TRUE(mod_info->vma_modify(self)); + signal_state(mod_info, SETUP_MAPS_MODIFIED); + wait_for_state(mod_info, SETUP_RESTORE_MAPS); + ASSERT_TRUE(mod_info->vma_restore(self)); + signal_state(mod_info, SETUP_MAPS_RESTORED); + + wait_for_state(mod_info, TEST_READY); + while (mod_info->curr_state != TEST_DONE) { + ASSERT_TRUE(mod_info->vma_modify(self)); + ASSERT_TRUE(mod_info->vma_restore(self)); + } + } + for (i = 0; i < mod_info->vma_count; i++) + munmap(mod_info->child_mapped_addr[i], self->page_size * 3); + + exit(0); + } + + sprintf(fname, "/proc/%d/maps", self->pid); + self->maps_fd = open(fname, O_RDONLY); + ASSERT_NE(self->maps_fd, -1); + + /* Wait for the child to map the VMAs */ + wait_for_state(mod_info, CHILD_READY); + + /* Read first two pages */ + self->page1.data = malloc(self->page_size); + ASSERT_NE(self->page1.data, NULL); + self->page2.data = malloc(self->page_size); + ASSERT_NE(self->page2.data, NULL); + + ASSERT_TRUE(read_boundary_lines(self, &self->last_line, &self->first_line)); + + /* + * Find the addresses corresponding to the last line in the first page + * and the first line in the last page. + */ + mod_info->addr = NULL; + mod_info->next_addr = NULL; + for (int i = 0; i < mod_info->vma_count; i++) { + if (mod_info->child_mapped_addr[i] == (void *)self->last_line.start_addr) { + mod_info->addr = mod_info->child_mapped_addr[i]; + mod_info->prot = PROT_READ; + /* Even VMAs have write permission */ + if ((i % 2) == 0) + mod_info->prot |= PROT_WRITE; + } else if (mod_info->child_mapped_addr[i] == (void *)self->first_line.start_addr) { + mod_info->next_addr = mod_info->child_mapped_addr[i]; + } + + if (mod_info->addr && mod_info->next_addr) + break; + } + ASSERT_TRUE(mod_info->addr && mod_info->next_addr); + + signal_state(mod_info, PARENT_READY); + +} + +FIXTURE_TEARDOWN(proc_maps_race) +{ + int status; + + stop_vma_modifier(self->mod_info); + + free(self->page2.data); + free(self->page1.data); + + for (int i = 0; i < self->vma_count; i++) + munmap(self->mod_info->child_mapped_addr[i], self->page_size); + close(self->maps_fd); + waitpid(self->pid, &status, 0); + munmap(self->mod_info, self->shared_mem_size); +} + +TEST_F(proc_maps_race, test_maps_tearing_from_split) +{ + struct vma_modifier_info *mod_info = self->mod_info; + + struct line_content split_last_line; + struct line_content split_first_line; + struct line_content restored_last_line; + struct line_content restored_first_line; + + wait_for_state(mod_info, SETUP_READY); + + /* re-read the file to avoid using stale data from previous test */ + ASSERT_TRUE(read_boundary_lines(self, &self->last_line, &self->first_line)); + + mod_info->vma_modify = split_vma; + mod_info->vma_restore = merge_vma; + mod_info->vma_mod_check = check_split_result; + + ASSERT_TRUE(capture_mod_pattern(self, &split_last_line, &split_first_line, + &restored_last_line, &restored_first_line)); + + /* Now start concurrent modifications for self->duration_sec */ + signal_state(mod_info, TEST_READY); + + struct line_content new_last_line; + struct line_content new_first_line; + struct timespec start_ts, end_ts; + + clock_gettime(CLOCK_MONOTONIC_COARSE, &start_ts); + do { + bool last_line_changed; + bool first_line_changed; + + ASSERT_TRUE(read_boundary_lines(self, &new_last_line, &new_first_line)); + + /* Check if we read vmas after split */ + if (!strcmp(new_last_line.text, split_last_line.text)) { + /* + * The vmas should be consistent with split results, + * however if vma was concurrently restored after a + * split, it can be reported twice (first the original + * split one, then the same vma but extended after the + * merge) because we found it as the next vma again. + * In that case new first line will be the same as the + * last restored line. + */ + ASSERT_FALSE(strcmp(new_first_line.text, split_first_line.text) && + strcmp(new_first_line.text, restored_last_line.text)); + } else { + /* The vmas should be consistent with merge results */ + ASSERT_FALSE(strcmp(new_last_line.text, restored_last_line.text)); + ASSERT_FALSE(strcmp(new_first_line.text, restored_first_line.text)); + } + /* + * First and last lines should change in unison. If the last + * line changed then the first line should change as well and + * vice versa. + */ + last_line_changed = strcmp(new_last_line.text, self->last_line.text) != 0; + first_line_changed = strcmp(new_first_line.text, self->first_line.text) != 0; + ASSERT_EQ(last_line_changed, first_line_changed); + + clock_gettime(CLOCK_MONOTONIC_COARSE, &end_ts); + } while (end_ts.tv_sec - start_ts.tv_sec < self->duration_sec); + + /* Signal the modifyer thread to stop and wait until it exits */ + signal_state(mod_info, TEST_DONE); +} + +TEST_HARNESS_MAIN