selftests/proc: extend /proc/pid/maps tearing test to include vma remapping

Test that /proc/pid/maps does not report unexpected holes in the address
space when we concurrently remap a part of a vma into the middle of
another vma.  This remapping results in the destination vma being split
into three parts and the part in the middle being patched back from, all
done concurrently from under the reader.  We should always see either
original vma or the split one with no holes.

Link: https://lkml.kernel.org/r/20250719182854.3166724-4-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jeongjun Park <aha310510@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Cc: T.J. Mercier <tjmercier@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Ye Bin <yebin10@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/proc/proc-maps-race.c b/tools/testing/selftests/proc/proc-maps-race.c
index 19028bd3b85c69f5a2e5cf60517d971f342b82f9..bc614a2d944aa6616a5fb05dd243a7db19742e88 100644 (file)
--- a/tools/testing/selftests/proc/proc-maps-race.c
+++ b/tools/testing/selftests/proc/proc-maps-race.c
@@ -264,6 +264,35 @@ static inline bool check_shrink_result(struct line_content *mod_last_line,
               strcmp(mod_first_line->text, restored_first_line->text) == 0;
 }
 
+static inline bool remap_vma(FIXTURE_DATA(proc_maps_race) *self)
+{
+       /*
+        * Remap the last page of the next vma into the middle of the vma.
+        * This splits the current vma and the first and middle parts (the
+        * parts at lower addresses) become the last vma objserved in the
+        * first page and the first vma observed in the last page.
+        */
+       return mremap(self->mod_info->next_addr + self->page_size * 2, self->page_size,
+                     self->page_size, MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP,
+                     self->mod_info->addr + self->page_size) != MAP_FAILED;
+}
+
+static inline bool patch_vma(FIXTURE_DATA(proc_maps_race) *self)
+{
+       return mprotect(self->mod_info->addr + self->page_size, self->page_size,
+                       self->mod_info->prot) == 0;
+}
+
+static inline bool check_remap_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");
@@ -523,4 +552,61 @@ TEST_F(proc_maps_race, test_maps_tearing_from_resize)
        signal_state(mod_info, TEST_DONE);
 }
 
+TEST_F(proc_maps_race, test_maps_tearing_from_remap)
+{
+       struct vma_modifier_info *mod_info = self->mod_info;
+
+       struct line_content remapped_last_line;
+       struct line_content remapped_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 = remap_vma;
+       mod_info->vma_restore = patch_vma;
+       mod_info->vma_mod_check = check_remap_result;
+
+       ASSERT_TRUE(capture_mod_pattern(self, &remapped_last_line, &remapped_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 {
+               ASSERT_TRUE(read_boundary_lines(self, &new_last_line, &new_first_line));
+
+               /* Check if we read vmas after remapping it */
+               if (!strcmp(new_last_line.text, remapped_last_line.text)) {
+                       /*
+                        * The vmas should be consistent with remap results,
+                        * however if the vma was concurrently restored, it
+                        * can be reported twice (first as split one, then
+                        * as restored one) 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, remapped_first_line.text) &&
+                                    strcmp(new_first_line.text, restored_last_line.text));
+               } else {
+                       /* The vmas should be consistent with the original/resored state */
+                       ASSERT_FALSE(strcmp(new_last_line.text, restored_last_line.text));
+                       ASSERT_FALSE(strcmp(new_first_line.text, restored_first_line.text));
+               }
+
+               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