[v2] dm-crypt: fix softlockup in dmcrypt_write

Commit Message

yangerkun March 6, 2023, 11:56 a.m. UTC

From: yangerkun <[e-mail]>

We meet a softlockup:

localhost login: [ 3391.153255][   C12] watchdog: BUG: soft lockup - CPU#12 stuck for 23s! [dmcrypt_write/2:2897]
...
[ 3391.258372][   C12] CPU: 12 PID: 2897 Comm: dmcrypt_write/2 Tainted: G             L    5.10.0+ #8
[ 3391.267288][   C12] Hardware name: Huawei TaiShan 2280 V2/BC82AMDDA, BIOS 1.75 04/26/2021
[ 3391.275428][   C12] pstate: 80400009 (Nzcv daif +PAN -UAO -TCO BTYPE=--)
[ 3391.282102][   C12] pc : blk_attempt_bio_merge.part.6+0x38/0x158
[ 3391.288080][   C12] lr : blk_attempt_plug_merge+0xc0/0x1b0
[ 3391.293540][   C12] sp : ffff8000718abc30
[ 3391.297530][   C12] x29: ffff8000718abc30 x28: 0000000000000000
[ 3391.303509][   C12] x27: ffff2020361d9ac0 x26: 0000000000000001
[ 3391.309488][   C12] x25: 0000000000000001 x24: ffff8000718abd08
[ 3391.315467][   C12] x23: ffff0020a10dbb00 x22: 0000000000000001
[ 3391.321445][   C12] x21: ffff8000718abe20 x20: ffff0020a10dbb00
[ 3391.327424][   C12] x19: ffff0020aed7b040 x18: 0000000000000000
[ 3391.333402][   C12] x17: 0000000000000000 x16: fffffdffffe00000
[ 3391.339381][   C12] x15: 0000000000001000 x14: 0000000000000000
[ 3391.345359][   C12] x13: 0000000000002000 x12: ffff2060011f9070
[ 3391.351338][   C12] x11: 0000000000000001 x10: 0000000000000002
[ 3391.357316][   C12] x9 : ffff800010586c38 x8 : ffff202009a7f200
[ 3391.363294][   C12] x7 : ffff8000718abd00 x6 : ffff20200df33750
[ 3391.369274][   C12] x5 : 0000000000000001 x4 : 0000000000000000
[ 3391.375252][   C12] x3 : 0000000000000001 x2 : ffff0020a10dbb00
[ 3391.381230][   C12] x1 : ffff0020aed7b040 x0 : 0000000000001000
[ 3391.387210][   C12] Call trace:
[ 3391.390338][   C12]  blk_attempt_bio_merge.part.6+0x38/0x158
[ 3391.395970][   C12]  blk_attempt_plug_merge+0xc0/0x1b0
[ 3391.401085][   C12]  blk_mq_submit_bio+0x398/0x550
[ 3391.405856][   C12]  submit_bio_noacct+0x308/0x380
[ 3391.410630][   C12]  dmcrypt_write+0x1e4/0x208 [dm_crypt]
[ 3391.416005][   C12]  kthread+0x130/0x138
[ 3391.419911][   C12]  ret_from_fork+0x10/0x18

dmcrypt_write will be wakeup once there is a not empty write_tree, and
before really submit_bio, the old write_tree will be peeled, so there
may not so much bio, but every time we check RB_EMPTY_ROOT, it may be
false since the heavy load write, so the softlockup can trigger.

We can add cond_resched every time before or after kcryptd_io_write, but
dmcrypt_write seems performance sensitive since it will submit all
pending write, so we choose cond_resched after 1s before the 'while'
submit bio.

Fixes: dc2676210c42 ("dm crypt: offload writes to thread")
Signed-off-by: yangerkun <[e-mail]>
---
 drivers/md/dm-crypt.c | 6 ++++++
 1 file changed, 6 insertions(+)

v1->v2:
change schedule() to cond_resched()

Patch

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 40cb1719ae4d..6a675257e00e 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -1894,6 +1894,7 @@  static int dmcrypt_write(void *data)
 {
 	struct crypt_config *cc = data;
 	struct dm_crypt_io *io;
+	unsigned long start_time = jiffies;
 
 	while (1) {
 		struct rb_root write_tree;
@@ -1916,6 +1917,7 @@  static int dmcrypt_write(void *data)
 
 		schedule();
 
+		start_time = jiffies;
 		set_current_state(TASK_RUNNING);
 		spin_lock_irq(&cc->write_thread_lock);
 		goto continue_locked;
@@ -1927,6 +1929,10 @@  static int dmcrypt_write(void *data)
 
 		BUG_ON(rb_parent(write_tree.rb_node));
 
+		if (time_is_before_jiffies(start_time + HZ)) {
+			cond_resched();
+			start_time = jiffies;
+		}
 		/*
 		 * Note: we cannot walk the tree here with rb_next because
 		 * the structures may be freed when kcryptd_io_write is called.