tests/cases/test-msync-16k.c

   1 /*
   2  * For some background: this unit test was created for a bug where
   3  * during page-out, we captured the file size without any locks and
   4  * then if a change happened to come in before we took the locks, we
   5  * would lose the remainder of the page.  The following illustrates
   6  * the scenario:
   7  *
   8  *                 <- 1 PG ->
   9  *                 a    b   c
  10  *   +-------------+--------+----
  11  *   |             |XXXX    |
  12  *   +-------------+--------+----
  13  *                     ^
  14  *                     |
  15  *                    EOF
  16  *
  17  * A page-out is requested for the page starting at @a and ending at
  18  * @c.  The end of the file is at @b and is captured before any locks
  19  * are taken.  After that, another thread writes something between @b
  20  * and @c.  The page-out then continues, but it thinks the end of the
  21  * file is at @b, so it will only write up to @b and then it will mark
  22  * the entire page as clean.  That will cause us to lose the data that
  23  * was written between @b and @c.  This would only occur if there is
  24  * an extent boundary at @b (which is the reason for the F_PREALLOCATE
  25  * calls below).  The syncer thread below is simulating what we do in
  26  * page-out: we write 1 MB chunks.
  27  */
  28
  29 #include <fcntl.h>
  30 #include <assert.h>
  31 #include <unistd.h>
  32 #include <string.h>
  33 #include <stdlib.h>
  34 #include <pthread.h>
  35 #include <sys/mman.h>
  36 #include <sys/errno.h>
  37 #include <sys/stat.h>
  38 #include <stdio.h>
  39 #include <sched.h>
  40
  41 #include "hfs-tests.h"
  42 #include "test-utils.h"
  43 #include "disk-image.h"
  44
  45 TEST(msync_16k)
  46
  47 static disk_image_t *di;
  48
  49 volatile off_t size = 0;
  50
  51 static int fd;
  52
  53 void syncer(void)
  54 {
  55         for (;;) {
  56                 off_t sz = size;
  57
  58                 if (sz == -1)
  59                         break;
  60
  61                 sz &= ~0xfffff;
  62
  63                 void *p = mmap(NULL, 0x100000, PROT_READ | PROT_WRITE, MAP_SHARED,
  64                                            fd, sz);
  65
  66                 assert_with_errno(p != MAP_FAILED);
  67
  68                 while ((size & ~0xfffff) == sz) {
  69                         assert_no_err(msync(p, 0x100000, MS_SYNC));
  70                         sched_yield();
  71                 }
  72
  73                 assert_no_err(munmap(p, 0x100000));
  74         }
  75 }
  76
  77 int run_msync_16k(__unused test_ctx_t *ctx)
  78 {
  79         di = disk_image_get();
  80
  81         char *file;
  82         asprintf(&file, "%s/msync-16k.data", di->mount_point);
  83
  84         char *buf = malloc(1024 * 1024);
  85         memset(buf, 0xaf, 1024 * 1024);
  86
  87         unlink(file);
  88
  89         fd = open(file, O_CREAT | O_RDWR, 0666);
  90         assert_with_errno(fd >= 0);
  91
  92         pthread_t thr;
  93         pthread_create(&thr, NULL, (void *(*)(void *))syncer, NULL);
  94
  95         assert_no_err(fcntl(fd, F_NOCACHE, 1));
  96
  97         check_io(write(fd, buf, 8192), 8192);
  98
  99         size = 8192;
 100         while (size < 100 * 1024 * 1024ll) {
 101                 // Force an extent boundary
 102                 struct log2phys l2p = {
 103                         .l2p_contigbytes = 4096,
 104                         .l2p_devoffset = size - 4096,
 105                 };
 106                 assert(!fcntl(fd, F_LOG2PHYS_EXT, &l2p));
 107
 108                 struct fstore fst = {
 109                         .fst_posmode = F_VOLPOSMODE,
 110                         .fst_offset = l2p.l2p_devoffset + 4096,
 111                         .fst_length = size + 16384,
 112                 };
 113                 assert(!fcntl(fd, F_PREALLOCATE, &fst));
 114
 115                 check_io(pwrite(fd, buf, 16384, size), 16384);
 116                 size += 16384;
 117         }
 118
 119         size_t sz = size;
 120         size = -1;
 121
 122         pthread_join(thr, NULL);
 123         assert_no_err(close(fd));
 124
 125         fd = open(file, O_RDWR);
 126
 127         assert_with_errno(fd >= 0);
 128         size_t done = 0;
 129         char *cmp_buf = malloc(1024 * 1024);
 130
 131         while (done < sz) {
 132                 void *p = mmap(NULL, 1024 * 1024, PROT_READ | PROT_WRITE, MAP_SHARED, fd, done);
 133                 assert_with_errno(p != MAP_FAILED);
 134                 assert_no_err(msync(p, 1024 * 1024, MS_INVALIDATE | MS_SYNC));
 135                 assert_no_err(munmap(p, 1024 * 1024));
 136
 137                 bzero(cmp_buf, 1024 * 1024);
 138                 ssize_t amt = read(fd, cmp_buf, 1024 * 1024);
 139                 assert(amt > 0);
 140                 assert(!memcmp(cmp_buf, buf, amt));
 141                 done += amt;
 142         }
 143
 144         assert_no_err(close(fd));
 145
 146         assert_no_err(unlink(file));
 147
 148         free(file);
 149
 150         return 0;
 151 }