lkml.org 
[lkml]   [2023]   [Mar]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
SubjectRe: [PATCH -next 1/6] Revert "md: unlock mddev before reap sync_thread in action_store"
From
Date
Hi,

在 2023/03/22 15:19, Guoqing Jiang 写道:
>
>
> On 3/22/23 14:41, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> This reverts commit 9dfbdafda3b34e262e43e786077bab8e476a89d1.
>>
>> Because it will introduce a defect that sync_thread can be running while
>> MD_RECOVERY_RUNNING is cleared, which will cause some unexpected
>> problems,
>> for example:
>>
>> list_add corruption. prev->next should be next (ffff0001ac1daba0), but
>> was ffff0000ce1a02a0. (prev=ffff0000ce1a02a0).
>> Call trace:
>>   __list_add_valid+0xfc/0x140
>>   insert_work+0x78/0x1a0
>>   __queue_work+0x500/0xcf4
>>   queue_work_on+0xe8/0x12c
>>   md_check_recovery+0xa34/0xf30
>>   raid10d+0xb8/0x900 [raid10]
>>   md_thread+0x16c/0x2cc
>>   kthread+0x1a4/0x1ec
>>   ret_from_fork+0x10/0x18
>>
>> This is because work is requeued while it's still inside workqueue:
>
> If the workqueue subsystem can have such problem because of md flag,
> then I have to think workqueue is fragile.
>
>> t1:            t2:
>> action_store
>>   mddev_lock
>>    if (mddev->sync_thread)
>>     mddev_unlock
>>     md_unregister_thread
>>     // first sync_thread is done
>>             md_check_recovery
>>              mddev_try_lock
>>              /*
>>               * once MD_RECOVERY_DONE is set, new sync_thread
>>               * can start.
>>               */
>>              set_bit(MD_RECOVERY_RUNNING, &mddev->recovery)
>>              INIT_WORK(&mddev->del_work, md_start_sync)
>>              queue_work(md_misc_wq, &mddev->del_work)
>>               test_and_set_bit(WORK_STRUCT_PENDING_BIT, ...)
>
> Assume you mean below,
>
> 1551 if(!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
> 1552                 __queue_work(cpu, wq, work);
> 1553                 ret = true;
> 1554         }
>
> Could you explain how the same work can be re-queued? Isn't the PENDING_BIT
> is already set in t3? I believe queue_work shouldn't do that per the
> comment
> but I am not expert ...

This is not related to workqueue, it is just because raid10
reinitialize the work that is already queued, like I discribed later
in t3:

t2:
md_check_recovery:
INIT_WORK -> clear pending
queue_work -> set pending
list_add_tail
...

t3: -> work is still pending
md_check_recovery:
INIT_WORK -> clear pending
queue_work -> set pending
list_add_tail -> list is corrupted

>
> Returns %false if @work was already on a queue, %true otherwise.
>
>>               // set pending bit
>>               insert_work
>>                list_add_tail
>>              mddev_unlock
>>     mddev_lock_nointr
>>     md_reap_sync_thread
>>     // MD_RECOVERY_RUNNING is cleared
>>   mddev_unlock
>>
>> t3:
>>
>> // before queued work started from t2
>> md_check_recovery
>>   // MD_RECOVERY_RUNNING is not set, a new sync_thread can be started
>>   INIT_WORK(&mddev->del_work, md_start_sync)
>>    work->data = 0
>>    // work pending bit is cleared
>>   queue_work(md_misc_wq, &mddev->del_work)
>>    insert_work
>>     list_add_tail
>>     // list is corrupted
>>
>> This patch revert the commit to fix the problem, the deadlock this
>> commit tries to fix will be fixed in following patches.
>
> Pls cc the previous users who had encounter the problem to test the
> second patch.

Ok, cc Marc. Can you try if this patchset fix the problem you reproted
in the following thread?

md_raid: mdX_raid6 looping after sync_action "check" to "idle"
transition
>
> And can you share your test which can trigger the re-queued issue?
> I'd like to try with latest mainline such as 6.3-rc3, and your test is
> not only run against 5.10 kernel as you described before, right?
>

Of course, our 5.10 and mainline are the same,

there are some tests:

First the deadlock can be reporduced reliably, test script is simple:

mdadm -Cv /dev/md0 -n 4 -l10 /dev/sd[abcd]

fio -filename=/dev/md0 -rw=randwrite -direct=1 -name=a -bs=4k
-numjobs=16 -iodepth=16 &

echo -1 > /sys/kernel/debug/fail_make_request/times
echo 1 > /sys/kernel/debug/fail_make_request/probability
echo 1 > /sys/block/sda/make-it-fail

{
while true; do
mdadm -f /dev/md0 /dev/sda
mdadm -r /dev/md0 /dev/sda
mdadm --zero-superblock /dev/sda
mdadm -a /dev/md0 /dev/sda
sleep 2
done
} &

{
while true; do
mdadm -f /dev/md0 /dev/sdd
mdadm -r /dev/md0 /dev/sdd
mdadm --zero-superblock /dev/sdd
mdadm -a /dev/md0 /dev/sdd
sleep 10
done
} &

{
while true; do
echo frozen > /sys/block/md0/md/sync_action
echo idle > /sys/block/md0/md/sync_action
sleep 0.1
done
} &

Then, the problem MD_RECOVERY_RUNNING can be cleared can't be reporduced
reliably, usually it takes 2+ days to triggered a problem, and each time
problem phenomenon can be different, I'm hacking the kernel and add
some BUG_ON to test MD_RECOVERY_RUNNING in attached patch, following
test can trigger the BUG_ON:

mdadm -Cv /dev/md0 -e1.0 -n 4 -l 10 /dev/sd{a..d} --run
sleep 5
echo 1 > /sys/module/md_mod/parameters/set_delay
echo idle > /sys/block/md0/md/sync_action &
sleep 5
echo "want_replacement" > /sys/block/md0/md/dev-sdd/state

test result:

[ 228.390237] md_check_recovery: running is set
[ 228.391376] md_check_recovery: queue new sync thread
[ 233.671041] action_store unregister success! delay 10s
[ 233.689276] md_check_recovery: running is set
[ 238.722448] md_check_recovery: running is set
[ 238.723328] md_check_recovery: queue new sync thread
[ 238.724851] md_do_sync: before new wor, sleep 10s
[ 239.725818] md_do_sync: delay done
[ 243.674828] action_store delay done
[ 243.700102] md_reap_sync_thread: running is cleared!
[ 243.748703] ------------[ cut here ]------------
[ 243.749656] kernel BUG at drivers/md/md.c:9084!
[ 243.750548] invalid opcode: 0000 [#1] PREEMPT SMP
[ 243.752028] CPU: 6 PID: 1495 Comm: md0_resync Not tainted
6.3.0-rc1-next-20230310-00001-g4b3965bcb967-dirty #47
[ 243.755030] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31
04/01/2014
[ 243.758516] RIP: 0010:md_do_sync+0x16a9/0x1b00
[ 243.759583] Code: ff 48 83 05 60 ce a7 0c 01 e9 8d f9 ff ff 48 83 05
13 ce a7 0c 01 48 c7 c6 e9 e0 29 83 e9 3b f9 ff ff 48 83 05 5f d0 a7 0c
01 <0f> 0b 48 83 05 5d d0 a7 0c 01 e8 f8 d5 0b0
[ 243.763661] RSP: 0018:ffffc90003847d50 EFLAGS: 00010202
[ 243.764212] RAX: 0000000000000028 RBX: ffff88817b529000 RCX:
0000000000000000
[ 243.764936] RDX: 0000000000000000 RSI: 0000000000000206 RDI:
ffff888100040740
[ 243.765648] RBP: 00000000002d6780 R08: 0101010101010101 R09:
ffff888165671d80
[ 243.766352] R10: ffffffff8ad6096c R11: ffff88816fcfa9f0 R12:
0000000000000001
[ 243.767066] R13: ffff888173920040 R14: ffff88817b529000 R15:
0000000000187100
[ 243.767781] FS: 0000000000000000(0000) GS:ffff888ffef80000(0000)
knlGS:0000000000000000
[ 243.768588] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 243.769172] CR2: 00005599effa8451 CR3: 00000001663e6000 CR4:
00000000000006e0
[ 243.769888] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[ 243.770598] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400
[ 243.771300] Call Trace:
[ 243.771555] <TASK>
[ 243.771779] ? kvm_clock_read+0x14/0x30
[ 243.772169] ? kvm_sched_clock_read+0x9/0x20
[ 243.772611] ? sched_clock_cpu+0x21/0x330
[ 243.773023] md_thread+0x2ec/0x300
[ 243.773373] ? md_write_start+0x420/0x420
[ 243.773845] kthread+0x13e/0x1a0
[ 243.774210] ? kthread_exit+0x50/0x50
[ 243.774591] ret_from_fork+0x1f/0x30

> Thanks,
> Guoqing
>
> .
>
From 0f82a9298db4b3711863022dc0805c908db3bb98 Mon Sep 17 00:00:00 2001
From: Li Nan <linan122@huawei.com>
Date: Mon, 20 Mar 2023 16:53:08 +0800
Subject: [PATCH] echo idle

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
drivers/md/md.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 546b1b81eb28..196810067f29 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -4753,6 +4753,7 @@ action_show(struct mddev *mddev, char *page)
return sprintf(page, "%s\n", type);
}

+static bool set_delay = false;
static ssize_t
action_store(struct mddev *mddev, const char *page, size_t len)
{
@@ -4775,6 +4776,11 @@ action_store(struct mddev *mddev, const char *page, size_t len)
mddev_unlock(mddev);
set_bit(MD_RECOVERY_INTR, &mddev->recovery);
md_unregister_thread(&mddev->sync_thread);
+ if (set_delay) {
+ printk("%s unregister success! delay 10s\n", __func__);
+ mdelay(10000);
+ printk("%s delay done\n", __func__);
+ }
mddev_lock_nointr(mddev);
/*
* set RECOVERY_INTR again and restore reshape
@@ -8700,6 +8706,13 @@ void md_do_sync(struct md_thread *thread)
struct blk_plug plug;
int ret;

+ if (set_delay) {
+ printk("%s: before new wor, sleep 10s\n", __func__);
+ mdelay(1000);
+ printk("%s: delay done\n", __func__);
+ }
+ BUG_ON(!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery));
+
/* just incase thread restarts... */
if (test_bit(MD_RECOVERY_DONE, &mddev->recovery) ||
test_bit(MD_RECOVERY_WAIT, &mddev->recovery))
@@ -8899,6 +8912,7 @@ void md_do_sync(struct md_thread *thread)

skipped = 0;

+ BUG_ON(!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery));
if (!test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
((mddev->curr_resync > mddev->curr_resync_completed &&
(mddev->curr_resync - mddev->curr_resync_completed)
@@ -9067,6 +9081,7 @@ void md_do_sync(struct md_thread *thread)
/* set CHANGE_PENDING here since maybe another update is needed,
* so other nodes are informed. It should be harmless for normal
* raid */
+ BUG_ON(!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery));
set_mask_bits(&mddev->sb_flags, 0,
BIT(MD_SB_CHANGE_PENDING) | BIT(MD_SB_CHANGE_DEVS));

@@ -9361,6 +9376,7 @@ void md_check_recovery(struct mddev *mddev)
mddev->curr_resync_completed = 0;
spin_lock(&mddev->lock);
set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
+ printk("%s: running is set\n", __func__);
spin_unlock(&mddev->lock);
/* Clear some bits that don't mean anything, but
* might be left set
@@ -9405,6 +9421,9 @@ void md_check_recovery(struct mddev *mddev)
*/
md_bitmap_write_all(mddev->bitmap);
}
+
+ printk("%s: queue new sync thread\n", __func__);
+ BUG_ON(!test_bit(MD_RECOVERY_RUNNING, &mddev->recovery));
INIT_WORK(&mddev->del_work, md_start_sync);
queue_work(md_misc_wq, &mddev->del_work);
goto unlock;
@@ -9463,6 +9482,7 @@ void md_reap_sync_thread(struct mddev *mddev)
if (test_and_clear_bit(MD_CLUSTER_RESYNC_LOCKED, &mddev->flags))
md_cluster_ops->resync_finish(mddev);
clear_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
+ printk("%s: running is cleared!\n", __func__);
clear_bit(MD_RECOVERY_DONE, &mddev->recovery);
clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
clear_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
@@ -9956,6 +9976,7 @@ module_param_call(start_ro, set_ro, get_ro, NULL, S_IRUSR|S_IWUSR);
module_param(start_dirty_degraded, int, S_IRUGO|S_IWUSR);
module_param_call(new_array, add_named_array, NULL, NULL, S_IWUSR);
module_param(create_on_open, bool, S_IRUSR|S_IWUSR);
+module_param(set_delay, bool, S_IRUSR|S_IWUSR);

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("MD RAID framework");
--
2.31.1
\
 
 \ /
  Last update: 2023-03-27 01:12    [W:0.826 / U:0.012 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site