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Date: Fri, 2 Sep 2022 09:21:33 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Logan Gunthorpe <logang@...tatee.com>,
Yu Kuai <yukuai1@...weicloud.com>, song@...nel.org
Cc: linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
yi.zhang@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next 2/3] md/raid10: convert resync_lock to use seqlock
Hi,
在 2022/09/02 2:41, Logan Gunthorpe 写道:
> Hi,
>
> On 2022-08-29 07:15, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@...wei.com>
>>
>> Currently, wait_barrier() will hold 'resync_lock' to read 'conf->barrier',
>> and io can't be dispatched until 'barrier' is dropped.
>>
>> Since holding the 'barrier' is not common, convert 'resync_lock' to use
>> seqlock so that holding lock can be avoided in fast path.
>>
>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
>
> I've found some lockdep issues starting with this patch in md-next while
> running mdadm tests (specifically 00raid10 when run about 10 times in a
> row).
>
> I've seen a couple different lock dep errors. The first seems to be
> reproducible on this patch, then it possibly changes to the second on
> subsequent patches. Not sure exactly.
>
Thanks for the test,
I think this is false positive because of the special usage here,
for example, in raise_barrier():
write_seqlock_irq
spin_lock_irq();
lock_acquire
do_write_seqcount_begin
seqcount_acquire
wait_event_lock_irq_cmd
spin_unlock_irq -> lock is released while seqcount is still hold
if other context hold the lock again, lockdep
will trigger warning.
...
spin_lock_irq
write_sequnlock_irq
Functionality should be ok, I'll try to find a way to prevent such
warning.
Thanks,
Kuai
> I haven't dug into it too deeply, but hopefully it can be fixed easily.
>
> Logan
>
> --
>
>
> ================================
> WARNING: inconsistent lock state
> 6.0.0-rc2-eid-vmlocalyes-dbg-00023-gfd68041d2fd2 #2604 Not tainted
> --------------------------------
> inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage.
> fsck.ext3/1695 [HC0[0]:SC0[0]:HE0:SE1] takes:
> ffff8881049b0120 (&____s->seqcount#10){+.?.}-{0:0}, at:
> raid10_read_request+0x21f/0x760
> (raid10.c:1134)
>
> {IN-SOFTIRQ-W} state was registered at:
> lock_acquire+0x183/0x440
> lower_barrier+0x5e/0xd0
> end_sync_request+0x178/0x180
> end_sync_write+0x193/0x380
> bio_endio+0x346/0x3a0
> blk_update_request+0x1eb/0x7c0
> blk_mq_end_request+0x30/0x50
> lo_complete_rq+0xb7/0x100
> blk_complete_reqs+0x77/0x90
> blk_done_softirq+0x38/0x40
> __do_softirq+0x10c/0x650
> run_ksoftirqd+0x48/0x80
> smpboot_thread_fn+0x302/0x400
> kthread+0x18c/0x1c0
> ret_from_fork+0x1f/0x30
>
> irq event stamp: 8930
> hardirqs last enabled at (8929): [<ffffffff96df8351>]
> _raw_spin_unlock_irqrestore+0x31/0x60
> hardirqs last disabled at (8930): [<ffffffff96df7fc5>]
> _raw_spin_lock_irq+0x75/0x90
> softirqs last enabled at (6768): [<ffffffff9554970e>]
> __irq_exit_rcu+0xfe/0x150
> softirqs last disabled at (6757): [<ffffffff9554970e>]
> __irq_exit_rcu+0xfe/0x150
>
> other info that might help us debug this:
> Possible unsafe locking scenario:
>
> CPU0
> ----
> lock(&____s->seqcount#10);
> <Interrupt>
> lock(&____s->seqcount#10);
>
> *** DEADLOCK ***
>
> 2 locks held by fsck.ext3/1695:
> #0: ffff8881007d0930 (mapping.invalidate_lock#2){++++}-{3:3}, at:
> page_cache_ra_unbounded+0xaf/0x250
> #1: ffff8881049b0120 (&____s->seqcount#10){+.?.}-{0:0}, at:
> raid10_read_request+0x21f/0x760
>
> stack backtrace:
> CPU: 0 PID: 1695 Comm: fsck.ext3 Not tainted
> 6.0.0-rc2-eid-vmlocalyes-dbg-00023-gfd68041d2fd2 #2604
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2
> 04/01/2014
> Call Trace:
> <TASK>
> dump_stack_lvl+0x5a/0x74
> dump_stack+0x10/0x12
> print_usage_bug.part.0+0x233/0x246
> mark_lock.part.0.cold+0x73/0x14f
> mark_held_locks+0x71/0xa0
> lockdep_hardirqs_on_prepare+0x158/0x230
> trace_hardirqs_on+0x34/0x100
> _raw_spin_unlock_irq+0x28/0x60
> wait_barrier+0x4a6/0x720
> raid10.c:1004
> raid10_read_request+0x21f/0x760
> raid10_make_request+0x2d6/0x2160
> md_handle_request+0x3f3/0x5b0
> md_submit_bio+0xd9/0x120
> __submit_bio+0x9d/0x100
> submit_bio_noacct_nocheck+0x1fd/0x470
> submit_bio_noacct+0x4c2/0xbb0
> submit_bio+0x3f/0xf0
> mpage_readahead+0x323/0x3b0
> blkdev_readahead+0x15/0x20
> read_pages+0x136/0x7a0
> page_cache_ra_unbounded+0x18d/0x250
> page_cache_ra_order+0x2c9/0x400
> ondemand_readahead+0x320/0x730
> page_cache_sync_ra+0xa6/0xb0
> filemap_get_pages+0x1eb/0xc00
> filemap_read+0x1f1/0x770
> blkdev_read_iter+0x164/0x310
> vfs_read+0x467/0x5a0
> __x64_sys_pread64+0x122/0x160
> do_syscall_64+0x35/0x80
> entry_SYSCALL_64_after_hwframe+0x46/0xb0
>
> --
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 6.0.0-rc2-eid-vmlocalyes-dbg-00027-gcd6aa5181bbb #2600 Not tainted
> ------------------------------------------------------
> systemd-udevd/292 is trying to acquire lock:
> ffff88817b644170 (&(&conf->resync_lock)->lock){....}-{2:2}, at:
> wait_barrier+0x4fe/0x770
>
> but task is already holding lock:
> ffff88817b644120 (&____s->seqcount#11){+.+.}-{0:0}, at:
> raid10_read_request+0x21f/0x760
> raid10.c:1140 wait_barrier()
> raid10.c:1204 regular_request_wait()
>
>
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&____s->seqcount#11){+.+.}-{0:0}:
> raise_barrier+0xe0/0x300
> raid10.c:940 write_seqlock_irq()
> raid10_sync_request+0x629/0x4750
> raid10.c:3689 raise_barrire()
> md_do_sync.cold+0x8ec/0x1491
> md_thread+0x19d/0x2d0
> kthread+0x18c/0x1c0
> ret_from_fork+0x1f/0x30
>
> -> #0 (&(&conf->resync_lock)->lock){....}-{2:2}:
> __lock_acquire+0x1cb4/0x3170
> lock_acquire+0x183/0x440
> _raw_spin_lock_irq+0x4d/0x90
> wait_barrier+0x4fe/0x770
> raid10_read_request+0x21f/0x760
> raid10.c:1140 wait_barrier()
> raid10.c:1204 regular_request_wait()
> raid10_make_request+0x2d6/0x2190
> md_handle_request+0x3f3/0x5b0
> md_submit_bio+0xd9/0x120
> __submit_bio+0x9d/0x100
> submit_bio_noacct_nocheck+0x1fd/0x470
> submit_bio_noacct+0x4c2/0xbb0
> submit_bio+0x3f/0xf0
> submit_bh_wbc+0x270/0x2a0
> block_read_full_folio+0x37c/0x580
> blkdev_read_folio+0x18/0x20
> filemap_read_folio+0x3f/0x110
> do_read_cache_folio+0x13b/0x2c0
> read_cache_folio+0x42/0x50
> read_part_sector+0x74/0x1c0
> read_lba+0x176/0x2a0
> efi_partition+0x1ce/0xdd0
> bdev_disk_changed+0x2e7/0x6a0
> blkdev_get_whole+0xd2/0x140
> blkdev_get_by_dev.part.0+0x37f/0x570
> blkdev_get_by_dev+0x51/0x60
> disk_scan_partitions+0xad/0xf0
> blkdev_common_ioctl+0x3f3/0xdf0
> blkdev_ioctl+0x1e1/0x450
> __x64_sys_ioctl+0xc0/0x100
> do_syscall_64+0x35/0x80
> entry_SYSCALL_64_after_hwframe+0x46/0xb0
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&____s->seqcount#11);
> lock(&(&conf->resync_lock)->lock);
> lock(&____s->seqcount#11);
> lock(&(&conf->resync_lock)->lock);
>
> *** DEADLOCK ***
>
> 2 locks held by systemd-udevd/292:
> #0: ffff88817a532528 (&disk->open_mutex){+.+.}-{3:3}, at:
> blkdev_get_by_dev.part.0+0x180/0x570
> #1: ffff88817b644120 (&____s->seqcount#11){+.+.}-{0:0}, at:
> raid10_read_request+0x21f/0x760
>
> stack backtrace:
> CPU: 3 PID: 292 Comm: systemd-udevd Not tainted
> 6.0.0-rc2-eid-vmlocalyes-dbg-00027-gcd6aa5181bbb #2600
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2
> 04/01/2014
> Call Trace:
> <TASK>
> dump_stack_lvl+0x5a/0x74
> dump_stack+0x10/0x12
> print_circular_bug.cold+0x146/0x14b
> check_noncircular+0x1ff/0x250
> __lock_acquire+0x1cb4/0x3170
> lock_acquire+0x183/0x440
> _raw_spin_lock_irq+0x4d/0x90
> wait_barrier+0x4fe/0x770
> raid10_read_request+0x21f/0x760
> raid10_make_request+0x2d6/0x2190
> md_handle_request+0x3f3/0x5b0
> md_submit_bio+0xd9/0x120
> __submit_bio+0x9d/0x100
> submit_bio_noacct_nocheck+0x1fd/0x470
> submit_bio_noacct+0x4c2/0xbb0
> submit_bio+0x3f/0xf0
> submit_bh_wbc+0x270/0x2a0
> block_read_full_folio+0x37c/0x580
> blkdev_read_folio+0x18/0x20
> filemap_read_folio+0x3f/0x110
> do_read_cache_folio+0x13b/0x2c0
> read_cache_folio+0x42/0x50
> read_part_sector+0x74/0x1c0
> read_lba+0x176/0x2a0
> efi_partition+0x1ce/0xdd0
> bdev_disk_changed+0x2e7/0x6a0
> blkdev_get_whole+0xd2/0x140
> blkdev_get_by_dev.part.0+0x37f/0x570
> blkdev_get_by_dev+0x51/0x60
> disk_scan_partitions+0xad/0xf0
> blkdev_common_ioctl+0x3f3/0xdf0
> blkdev_ioctl+0x1e1/0x450
> __x64_sys_ioctl+0xc0/0x100
> do_syscall_64+0x35/0x80
> .
>
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