Recent changes (master)

[Jens Axboe <axboe@kernel.dk>]

The following changes since commit 6f9cdcfcc7598c7d7b19c4a5120a251a80dab183:

  iolog: don't truncate time values (2023-10-02 14:29:29 +0000)

are available in the Git repository at:

  git://git.kernel.dk/fio.git master

for you to fetch changes up to 16b9f29dab1d105951da663474ec243942fda400:

  Merge branch 'fix-stat-overflow' of https://github.com/stilor/fio (2023-10-06 15:27:23 -0400)

----------------------------------------------------------------
Alexey Neyman (2):
      Change memcpy() calls to assignments
      Handle 32-bit overflows in disk utilization stats

Vincent Fu (1):
      Merge branch 'fix-stat-overflow' of https://github.com/stilor/fio

 diskutil.c | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

---

Diff of recent changes:

diff --git a/diskutil.c b/diskutil.c
index cf4ede85..69b3dd26 100644
--- a/diskutil.c
+++ b/diskutil.c
@@ -77,6 +77,23 @@ static int get_io_ticks(struct disk_util *du, struct disk_util_stat *dus)
 	return ret != 10;
 }
 
+static uint64_t safe_32bit_diff(uint64_t nval, uint64_t oval)
+{
+	/* Linux kernel prints some of the stat fields as 32-bit integers. It is
+	 * possible that the value overflows, but since fio uses unsigned 64-bit
+	 * arithmetic in update_io_tick_disk(), it instead results in a huge
+	 * bogus value being added to the respective accumulating field. Just
+	 * in case Linux starts reporting these metrics as 64-bit values in the
+	 * future, check that overflow actually happens around the 32-bit
+	 * unsigned boundary; assume overflow only happens once between
+	 * successive polls.
+	 */
+	if (oval <= nval || oval >= (1ull << 32))
+		return nval - oval;
+	else
+		return (1ull << 32) + nval - oval;
+}
+
 static void update_io_tick_disk(struct disk_util *du)
 {
 	struct disk_util_stat __dus, *dus, *ldus;
@@ -96,15 +113,16 @@ static void update_io_tick_disk(struct disk_util *du)
 	dus->s.ios[1] += (__dus.s.ios[1] - ldus->s.ios[1]);
 	dus->s.merges[0] += (__dus.s.merges[0] - ldus->s.merges[0]);
 	dus->s.merges[1] += (__dus.s.merges[1] - ldus->s.merges[1]);
-	dus->s.ticks[0] += (__dus.s.ticks[0] - ldus->s.ticks[0]);
-	dus->s.ticks[1] += (__dus.s.ticks[1] - ldus->s.ticks[1]);
-	dus->s.io_ticks += (__dus.s.io_ticks - ldus->s.io_ticks);
-	dus->s.time_in_queue += (__dus.s.time_in_queue - ldus->s.time_in_queue);
+	dus->s.ticks[0] += safe_32bit_diff(__dus.s.ticks[0], ldus->s.ticks[0]);
+	dus->s.ticks[1] += safe_32bit_diff(__dus.s.ticks[1], ldus->s.ticks[1]);
+	dus->s.io_ticks += safe_32bit_diff(__dus.s.io_ticks, ldus->s.io_ticks);
+	dus->s.time_in_queue +=
+			safe_32bit_diff(__dus.s.time_in_queue, ldus->s.time_in_queue);
 
 	fio_gettime(&t, NULL);
 	dus->s.msec += mtime_since(&du->time, &t);
-	memcpy(&du->time, &t, sizeof(t));
-	memcpy(&ldus->s, &__dus.s, sizeof(__dus.s));
+	du->time = t;
+	ldus->s = __dus.s;
 }
 
 int update_io_ticks(void)