When both regular IO and resync IO happen at the same time,
and if we also need to split regular. Then we can see tasks
hang due to barrier.
1. resync thread
[ 1463.757205] INFO: task md1_resync:5215 blocked for more than 480 seconds.
[ 1463.757207] Not tainted 4.19.5-1-default #1
[ 1463.757209] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1463.757212] md1_resync D 0 5215 2 0x80000000
[ 1463.757216] Call Trace:
[ 1463.757223] ? __schedule+0x29a/0x880
[ 1463.757231] ? raise_barrier+0x8d/0x140 [raid10]
[ 1463.757236] schedule+0x78/0x110
[ 1463.757243] raise_barrier+0x8d/0x140 [raid10]
[ 1463.757248] ? wait_woken+0x80/0x80
[ 1463.757257] raid10_sync_request+0x1f6/0x1e30 [raid10]
[ 1463.757265] ? _raw_spin_unlock_irq+0x22/0x40
[ 1463.757284] ? is_mddev_idle+0x125/0x137 [md_mod]
[ 1463.757302] md_do_sync.cold.78+0x404/0x969 [md_mod]
[ 1463.757311] ? wait_woken+0x80/0x80
[ 1463.757336] ? md_rdev_init+0xb0/0xb0 [md_mod]
[ 1463.757351] md_thread+0xe9/0x140 [md_mod]
[ 1463.757358] ? _raw_spin_unlock_irqrestore+0x2e/0x60
[ 1463.757364] ? __kthread_parkme+0x4c/0x70
[ 1463.757369] kthread+0x112/0x130
[ 1463.757374] ? kthread_create_worker_on_cpu+0x40/0x40
[ 1463.757380] ret_from_fork+0x3a/0x50
2. regular IO
[ 1463.760679] INFO: task kworker/0:8:5367 blocked for more than 480 seconds.
[ 1463.760683] Not tainted 4.19.5-1-default #1
[ 1463.760684] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1463.760687] kworker/0:8 D 0 5367 2 0x80000000
[ 1463.760718] Workqueue: md submit_flushes [md_mod]
[ 1463.760721] Call Trace:
[ 1463.760731] ? __schedule+0x29a/0x880
[ 1463.760741] ? wait_barrier+0xdd/0x170 [raid10]
[ 1463.760746] schedule+0x78/0x110
[ 1463.760753] wait_barrier+0xdd/0x170 [raid10]
[ 1463.760761] ? wait_woken+0x80/0x80
[ 1463.760768] raid10_write_request+0xf2/0x900 [raid10]
[ 1463.760774] ? wait_woken+0x80/0x80
[ 1463.760778] ? mempool_alloc+0x55/0x160
[ 1463.760795] ? md_write_start+0xa9/0x270 [md_mod]
[ 1463.760801] ? try_to_wake_up+0x44/0x470
[ 1463.760810] raid10_make_request+0xc1/0x120 [raid10]
[ 1463.760816] ? wait_woken+0x80/0x80
[ 1463.760831] md_handle_request+0x121/0x190 [md_mod]
[ 1463.760851] md_make_request+0x78/0x190 [md_mod]
[ 1463.760860] generic_make_request+0x1c6/0x470
[ 1463.760870] raid10_write_request+0x77a/0x900 [raid10]
[ 1463.760875] ? wait_woken+0x80/0x80
[ 1463.760879] ? mempool_alloc+0x55/0x160
[ 1463.760895] ? md_write_start+0xa9/0x270 [md_mod]
[ 1463.760904] raid10_make_request+0xc1/0x120 [raid10]
[ 1463.760910] ? wait_woken+0x80/0x80
[ 1463.760926] md_handle_request+0x121/0x190 [md_mod]
[ 1463.760931] ? _raw_spin_unlock_irq+0x22/0x40
[ 1463.760936] ? finish_task_switch+0x74/0x260
[ 1463.760954] submit_flushes+0x21/0x40 [md_mod]
So resync io is waiting for regular write io to complete to
decrease nr_pending (conf->barrier++ is called before waiting).
The regular write io splits another bio after call wait_barrier
which call nr_pending++, then the splitted bio would continue
with raid10_write_request -> wait_barrier, so the splitted bio
has to wait for barrier to be zero, then deadlock happens as
follows.
resync io regular io
raise_barrier
wait_barrier
generic_make_request
wait_barrier
To resolve the issue, we need to call allow_barrier to decrease
nr_pending before generic_make_request since regular IO is not
issued to underlying devices, and wait_barrier is called again
to ensure no internal IO happening.
Fixes: fc9977dd069e ("md/raid10: simplify the splitting of requests.")
Reported-and-tested-by: Siniša Bandin <sinisa@xxxxxxx>
Signed-off-by: Guoqing Jiang <gqjiang@xxxxxxxx>
---
drivers/md/raid10.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index b98e746e7fc4..12cf8a04e839 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1209,7 +1209,9 @@ static void raid10_read_request(struct mddev *mddev, struct bio *bio,
struct bio *split = bio_split(bio, max_sectors,
gfp, &conf->bio_split);
bio_chain(split, bio);
+ allow_barrier(conf);
generic_make_request(bio);
+ wait_barrier(conf);
bio = split;
r10_bio->master_bio = bio;
r10_bio->sectors = max_sectors;
@@ -1514,7 +1516,9 @@ static void raid10_write_request(struct mddev *mddev, struct bio *bio,
struct bio *split = bio_split(bio, r10_bio->sectors,
GFP_NOIO, &conf->bio_split);
bio_chain(split, bio);
+ allow_barrier(conf);
generic_make_request(bio);
+ wait_barrier(conf);
bio = split;
r10_bio->master_bio = bio;
}
--
2.13.7
