[PATCH 5.16 0118/1017] dm stats: fix too short end duration_ns when using precise_timestamps

Greg Kroah-Hartman
2022-04-05T12:03:55Z

From: Mike Snitzer <snitzer@redhat.com>

commit 0cdb90f0f306384ecbc60dfd6dc48cdbc1f2d0d8 upstream.

dm_stats_account_io()'s STAT_PRECISE_TIMESTAMPS support doesn't handle
the fact that with commit b879f915bc48 ("dm: properly fix redundant
bio-based IO accounting") io->start_time _may_ be in the past (meaning
the start_io_acct() was deferred until later).

Add a new dm_stats_recalc_precise_timestamps() helper that will
set/clear a new 'precise_timestamps' flag in the dm_stats struct based
on whether any configured stats enable STAT_PRECISE_TIMESTAMPS.
And update DM core's alloc_io() to use dm_stats_record_start() to set
stats_aux.duration_ns if stats->precise_timestamps is true.

Also, remove unused 'last_sector' and 'last_rw' members from the
dm_stats struct.

Fixes: b879f915bc48 ("dm: properly fix redundant bio-based IO accounting")
Cc: stable@vger.kernel.org
Co-developed-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/md/dm-stats.c | 28 +++++++++++++++++++++++++---
drivers/md/dm-stats.h | 9 +++++++--
drivers/md/dm.c | 2 ++
3 files changed, 34 insertions(+), 5 deletions(-)

--- a/drivers/md/dm-stats.c
+++ b/drivers/md/dm-stats.c
@@ -195,6 +195,7 @@ void dm_stats_init(struct dm_stats *stat

mutex_init(&stats->mutex);
INIT_LIST_HEAD(&stats->list);
+ stats->precise_timestamps = false;
stats->last = alloc_percpu(struct dm_stats_last_position);
for_each_possible_cpu(cpu) {
last = per_cpu_ptr(stats->last, cpu);
@@ -231,6 +232,22 @@ void dm_stats_cleanup(struct dm_stats *s
mutex_destroy(&stats->mutex);
}

+static void dm_stats_recalc_precise_timestamps(struct dm_stats *stats)
+{
+ struct list_head *l;
+ struct dm_stat *tmp_s;
+ bool precise_timestamps = false;
+
+ list_for_each(l, &stats->list) {
+ tmp_s = container_of(l, struct dm_stat, list_entry);
+ if (tmp_s->stat_flags & STAT_PRECISE_TIMESTAMPS) {
+ precise_timestamps = true;
+ break;
+ }
+ }
+ stats->precise_timestamps = precise_timestamps;
+}
+
static int dm_stats_create(struct dm_stats *stats, sector_t start, sector_t end,
sector_t step, unsigned stat_flags,
unsigned n_histogram_entries,
@@ -376,6 +393,9 @@ static int dm_stats_create(struct dm_sta
}
ret_id = s->id;
list_add_tail_rcu(&s->list_entry, l);
+
+ dm_stats_recalc_precise_timestamps(stats);
+
mutex_unlock(&stats->mutex);

resume_callback(md);
@@ -418,6 +438,9 @@ static int dm_stats_delete(struct dm_sta
}

list_del_rcu(&s->list_entry);
+
+ dm_stats_recalc_precise_timestamps(stats);
+
mutex_unlock(&stats->mutex);

/*
@@ -654,9 +677,8 @@ void dm_stats_account_io(struct dm_stats
got_precise_time = false;
list_for_each_entry_rcu(s, &stats->list, list_entry) {
if (s->stat_flags & STAT_PRECISE_TIMESTAMPS && !got_precise_time) {
- if (!end)
- stats_aux->duration_ns = ktime_to_ns(ktime_get());
- else
+ /* start (!end) duration_ns is set by DM core's alloc_io() */
+ if (end)
stats_aux->duration_ns = ktime_to_ns(ktime_get()) - stats_aux->duration_ns;
got_precise_time = true;
}
--- a/drivers/md/dm-stats.h
+++ b/drivers/md/dm-stats.h
@@ -13,8 +13,7 @@ struct dm_stats {
struct mutex mutex;
struct list_head list; /* list of struct dm_stat */
struct dm_stats_last_position __percpu *last;
- sector_t last_sector;
- unsigned last_rw;
+ bool precise_timestamps;
};

struct dm_stats_aux {
@@ -40,4 +39,10 @@ static inline bool dm_stats_used(struct
return !list_empty(&st->list);
}

+static inline void dm_stats_record_start(struct dm_stats *stats, struct dm_stats_aux *aux)
+{
+ if (unlikely(stats->precise_timestamps))
+ aux->duration_ns = ktime_to_ns(ktime_get());
+}
+
#endif
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -537,6 +537,8 @@ static struct dm_io *alloc_io(struct map

io->start_time = jiffies;

+ dm_stats_record_start(&md->stats, &io->stats_aux);
+
return io;
}