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Date: Tue, 22 Feb 2022 14:07:51 -0500
From: bfields@...ldses.org (J. Bruce Fields)
To: NeilBrown <neilb@...e.de>
Cc: Al Viro <viro@...iv.linux.org.uk>,
Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
Daire Byrne <daire@...g.com>,
Andreas Dilger <adilger.kernel@...ger.ca>
Subject: Re: [PATCH/RFC] VFS: support parallel updates in the one directory.
For what it's worth, I applied this to recent upstream (038101e6b2cd)
and fed it through my usual scripts--tests all passed, but I did see
this lockdep warning.
I'm not actually sure what was running at the time--probably just cthon.
--b.
[ 142.679891] ======================================================
[ 142.680883] WARNING: possible circular locking dependency detected
[ 142.681999] 5.17.0-rc5-00005-g64e79f877311 #1778 Not tainted
[ 142.682970] ------------------------------------------------------
[ 142.684059] test1/4557 is trying to acquire lock:
[ 142.684881] ffff888023d85398 (DENTRY_PAR_UPDATE){+.+.}-{0:0}, at: d_lock_update_nested+0x5/0x6a0
[ 142.686421]
but task is already holding lock:
[ 142.687171] ffff88801f618bd0 (&type->i_mutex_dir_key#6){++++}-{3:3}, at: path_openat+0x7cb/0x24a0
[ 142.689098]
which lock already depends on the new lock.
[ 142.690045]
the existing dependency chain (in reverse order) is:
[ 142.691171]
-> #1 (&type->i_mutex_dir_key#6){++++}-{3:3}:
[ 142.692285] down_write+0x82/0x130
[ 142.692844] vfs_rmdir+0xbd/0x560
[ 142.693351] do_rmdir+0x33d/0x400
[ 142.693830] __x64_sys_unlinkat+0xaf/0xe0
[ 142.694391] do_syscall_64+0x43/0x90
[ 142.694900] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 142.695609]
-> #0 (DENTRY_PAR_UPDATE){+.+.}-{0:0}:
[ 142.696357] __lock_acquire+0x2bfd/0x61b0
[ 142.696965] lock_acquire+0x1a6/0x4b0
[ 142.697489] d_lock_update_nested+0x8d/0x6a0
[ 142.698082] lookup_open.isra.0+0x1305/0x1bf0
[ 142.698685] path_openat+0x833/0x24a0
[ 142.699205] do_filp_open+0x197/0x3c0
[ 142.699725] do_sys_openat2+0xef/0x3d0
[ 142.700345] __x64_sys_creat+0xb4/0xf0
[ 142.700915] do_syscall_64+0x43/0x90
[ 142.701431] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 142.702112]
other info that might help us debug this:
[ 142.702872] Possible unsafe locking scenario:
[ 142.703492] CPU0 CPU1
[ 142.704115] ---- ----
[ 142.704704] lock(&type->i_mutex_dir_key#6);
[ 142.705296] lock(DENTRY_PAR_UPDATE);
[ 142.706065] lock(&type->i_mutex_dir_key#6);
[ 142.706911] lock(DENTRY_PAR_UPDATE);
[ 142.707382]
*** DEADLOCK ***
[ 142.707978] 2 locks held by test1/4557:
[ 142.708485] #0: ffff888011ef0438 (sb_writers#14){.+.+}-{0:0}, at: path_openat+0x1408/0x24a0
[ 142.709562] #1: ffff88801f618bd0 (&type->i_mutex_dir_key#6){++++}-{3:3}, at: path_openat+0x7cb/0x24a0
[ 142.710757]
stack backtrace:
[ 142.711187] CPU: 0 PID: 4557 Comm: test1 Not tainted 5.17.0-rc5-00005-g64e79f877311 #1778
[ 142.712275] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1.fc35 04/01/2014
[ 142.713409] Call Trace:
[ 142.713717] <TASK>
[ 142.713986] dump_stack_lvl+0x45/0x59
[ 142.714449] check_noncircular+0x23e/0x2e0
[ 142.714960] ? print_circular_bug+0x450/0x450
[ 142.715502] ? is_dynamic_key+0x1a0/0x1a0
[ 142.716061] ? _raw_spin_unlock_irqrestore+0x38/0x50
[ 142.716706] __lock_acquire+0x2bfd/0x61b0
[ 142.717246] ? do_syscall_64+0x43/0x90
[ 142.717712] ? entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 142.718361] ? lockdep_hardirqs_on_prepare+0x400/0x400
[ 142.719590] ? mark_lock.part.0+0xe7/0x2e00
[ 142.720217] lock_acquire+0x1a6/0x4b0
[ 142.720706] ? d_lock_update_nested+0x5/0x6a0
[ 142.721293] ? lock_release+0x6d0/0x6d0
[ 142.721774] ? lock_downgrade+0x690/0x690
[ 142.722280] ? do_raw_spin_unlock+0x54/0x220
[ 142.722814] d_lock_update_nested+0x8d/0x6a0
[ 142.723350] ? d_lock_update_nested+0x5/0x6a0
[ 142.723959] ? d_alloc_anon+0x10/0x10
[ 142.724443] ? kfree+0x110/0x250
[ 142.724887] ? lockdep_hardirqs_on+0x79/0x100
[ 142.725454] ? kfree+0x110/0x250
[ 142.725859] ? nfs_lookup+0x55a/0xa80 [nfs]
[ 142.726410] lookup_open.isra.0+0x1305/0x1bf0
[ 142.726952] ? lookup_positive_unlocked+0x80/0x80
[ 142.727546] ? rwsem_down_read_slowpath+0xaa0/0xaa0
[ 142.728239] path_openat+0x833/0x24a0
[ 142.728700] ? path_lookupat+0x6b0/0x6b0
[ 142.729233] ? lockdep_hardirqs_on_prepare+0x400/0x400
[ 142.729867] ? lockdep_hardirqs_on_prepare+0x400/0x400
[ 142.730502] do_filp_open+0x197/0x3c0
[ 142.730955] ? lock_is_held_type+0xd7/0x130
[ 142.731477] ? may_open_dev+0xd0/0xd0
[ 142.731994] ? do_raw_spin_lock+0x11e/0x240
[ 142.732545] ? do_raw_spin_unlock+0x54/0x220
[ 142.733115] ? getname_flags.part.0+0x8e/0x450
[ 142.733670] do_sys_openat2+0xef/0x3d0
[ 142.734140] ? mntput_no_expire+0x10f/0xad0
[ 142.734661] ? build_open_flags+0x450/0x450
[ 142.735179] ? dput+0x30/0xa10
[ 142.735565] __x64_sys_creat+0xb4/0xf0
[ 142.736091] ? __ia32_sys_openat2+0x260/0x260
[ 142.736656] ? syscall_enter_from_user_mode+0x1d/0x50
[ 142.737325] ? lockdep_hardirqs_on+0x79/0x100
[ 142.737885] do_syscall_64+0x43/0x90
[ 142.738333] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 142.738959] RIP: 0033:0x7f4c0f358e07
[ 142.739408] Code: 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 55 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 41 c3 48 83 ec 18 89 74 24 0c 48 89 3c 24 e8
[ 142.741911] RSP: 002b:00007ffe31b33e48 EFLAGS: 00000246 ORIG_RAX: 0000000000000055
[ 142.742843] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f4c0f358e07
[ 142.743718] RDX: 0000000000000000 RSI: 00000000000001b6 RDI: 00007ffe31b33e80
[ 142.744675] RBP: 00007ffe31b34e90 R08: 0000000000000000 R09: 00007ffe31b33be7
[ 142.745589] R10: fffffffffffff934 R11: 0000000000000246 R12: 0000000000401190
[ 142.746464] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[ 142.747343] </TASK>
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