[PATCH v2] blk-cgroup: Replace u64_sync with blkg_stat_lock for stats update

boy.wu
2024-07-10T06:13:43Z

From: Boy Wu <boy.wu@mediatek.com>

In 32bit SMP systems, if multiple CPUs call blkcg_print_stat,
which may cause blkcg_fill_root_iostats to have a concurrent problem
on the seqlock in u64_stats_update, which will cause a deadlock
on u64_stats_fetch_begin in blkcg_print_one_stat.

Thus use blkg_stat_lock to replace u64_sync.

Fixes: ef45fe470e1e ("blk-cgroup: show global disk stats in root cgroup io.stat")
Signed-off-by: Boy Wu <boy.wu@mediatek.com>
---
Change in v2:
- update commit message
- Remove u64_sync
- Replace spin_lock_irq with guard statement
- Replace blkg->q->queue_lock with blkg_stat_lock
---
block/blk-cgroup.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 85b3b9051455..18b47ee1a640 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -952,7 +952,6 @@ static void blkcg_fill_root_iostats(void)
struct blkcg_gq *blkg = bdev->bd_disk->queue->root_blkg;
struct blkg_iostat tmp;
int cpu;
- unsigned long flags;

memset(&tmp, 0, sizeof(tmp));
for_each_possible_cpu(cpu) {
@@ -974,9 +973,10 @@ static void blkcg_fill_root_iostats(void)
cpu_dkstats->sectors[STAT_DISCARD] << 9;
}

- flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
+#if BITS_PER_LONG == 32
+ guard(raw_spinlock_irqsave)(&blkg_stat_lock);
+#endif
blkg_iostat_set(&blkg->iostat.cur, &tmp);
- u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);
}
}

--
2.18.0