From: Guoqing Jiang gqjiang@suse.com
[ Upstream commit e820d55cb99dd93ac2dc949cf486bb187e5cd70d ]
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: SiniĊĦa Bandin sinisa@4net.rs Signed-off-by: Guoqing Jiang gqjiang@suse.com Signed-off-by: Shaohua Li shli@fb.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 @@ retry_write: 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; }