btrfs: fix lockdep splat when enabling and disabling qgroups
[ Upstream commit a855fbe6 ] When running test case btrfs/017 from fstests, lockdep reported the following splat: [ 1297.067385] ====================================================== [ 1297.067708] WARNING: possible circular locking dependency detected [ 1297.068022] 5.10.0-rc4-btrfs-next-73 #1 Not tainted [ 1297.068322] ------------------------------------------------------ [ 1297.068629] btrfs/189080 is trying to acquire lock: [ 1297.068929] ffff9f2725731690 (sb_internal#2){.+.+}-{0:0}, at: btrfs_quota_enable+0xaf/0xa70 [btrfs] [ 1297.069274] but task is already holding lock: [ 1297.069868] ffff9f2702b61a08 (&fs_info->qgroup_ioctl_lock){+.+.}-{3:3}, at: btrfs_quota_enable+0x3b/0xa70 [btrfs] [ 1297.070219] which lock already depends on the new lock. [ 1297.071131] the existing dependency chain (in reverse order) is: [ 1297.071721] -> #1 (&fs_info->qgroup_ioctl_lock){+.+.}-{3:3}: [ 1297.072375] lock_acquire+0xd8/0x490 [ 1297.072710] __mutex_lock+0xa3/0xb30 [ 1297.073061] btrfs_qgroup_inherit+0x59/0x6a0 [btrfs] [ 1297.073421] create_subvol+0x194/0x990 [btrfs] [ 1297.073780] btrfs_mksubvol+0x3fb/0x4a0 [btrfs] [ 1297.074133] __btrfs_ioctl_snap_create+0x119/0x1a0 [btrfs] [ 1297.074498] btrfs_ioctl_snap_create+0x58/0x80 [btrfs] [ 1297.074872] btrfs_ioctl+0x1a90/0x36f0 [btrfs] [ 1297.075245] __x64_sys_ioctl+0x83/0xb0 [ 1297.075617] do_syscall_64+0x33/0x80 [ 1297.075993] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 1297.076380] -> #0 (sb_internal#2){.+.+}-{0:0}: [ 1297.077166] check_prev_add+0x91/0xc60 [ 1297.077572] __lock_acquire+0x1740/0x3110 [ 1297.077984] lock_acquire+0xd8/0x490 [ 1297.078411] start_transaction+0x3c5/0x760 [btrfs] [ 1297.078853] btrfs_quota_enable+0xaf/0xa70 [btrfs] [ 1297.079323] btrfs_ioctl+0x2c60/0x36f0 [btrfs] [ 1297.079789] __x64_sys_ioctl+0x83/0xb0 [ 1297.080232] do_syscall_64+0x33/0x80 [ 1297.080680] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 1297.081139] other info that might help us debug this: [ 1297.082536] Possible unsafe locking scenario: [ 1297.083510] CPU0 CPU1 [ 1297.084005] ---- ---- [ 1297.084500] lock(&fs_info->qgroup_ioctl_lock); [ 1297.084994] lock(sb_internal#2); [ 1297.085485] lock(&fs_info->qgroup_ioctl_lock); [ 1297.085974] lock(sb_internal#2); [ 1297.086454] *** DEADLOCK *** [ 1297.087880] 3 locks held by btrfs/189080: [ 1297.088324] #0: ffff9f2725731470 (sb_writers#14){.+.+}-{0:0}, at: btrfs_ioctl+0xa73/0x36f0 [btrfs] [ 1297.088799] #1: ffff9f2702b60cc0 (&fs_info->subvol_sem){++++}-{3:3}, at: btrfs_ioctl+0x1f4d/0x36f0 [btrfs] [ 1297.089284] #2: ffff9f2702b61a08 (&fs_info->qgroup_ioctl_lock){+.+.}-{3:3}, at: btrfs_quota_enable+0x3b/0xa70 [btrfs] [ 1297.089771] stack backtrace: [ 1297.090662] CPU: 5 PID: 189080 Comm: btrfs Not tainted 5.10.0-rc4-btrfs-next-73 #1 [ 1297.091132] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 [ 1297.092123] Call Trace: [ 1297.092629] dump_stack+0x8d/0xb5 [ 1297.093115] check_noncircular+0xff/0x110 [ 1297.093596] check_prev_add+0x91/0xc60 [ 1297.094076] ? kvm_clock_read+0x14/0x30 [ 1297.094553] ? kvm_sched_clock_read+0x5/0x10 [ 1297.095029] __lock_acquire+0x1740/0x3110 [ 1297.095510] lock_acquire+0xd8/0x490 [ 1297.095993] ? btrfs_quota_enable+0xaf/0xa70 [btrfs] [ 1297.096476] start_transaction+0x3c5/0x760 [btrfs] [ 1297.096962] ? btrfs_quota_enable+0xaf/0xa70 [btrfs] [ 1297.097451] btrfs_quota_enable+0xaf/0xa70 [btrfs] [ 1297.097941] ? btrfs_ioctl+0x1f4d/0x36f0 [btrfs] [ 1297.098429] btrfs_ioctl+0x2c60/0x36f0 [btrfs] [ 1297.098904] ? do_user_addr_fault+0x20c/0x430 [ 1297.099382] ? kvm_clock_read+0x14/0x30 [ 1297.099854] ? kvm_sched_clock_read+0x5/0x10 [ 1297.100328] ? sched_clock+0x5/0x10 [ 1297.100801] ? sched_clock_cpu+0x12/0x180 [ 1297.101272] ? __x64_sys_ioctl+0x83/0xb0 [ 1297.101739] __x64_sys_ioctl+0x83/0xb0 [ 1297.102207] do_syscall_64+0x33/0x80 [ 1297.102673] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 1297.103148] RIP: 0033:0x7f773ff65d87 This is because during the quota enable ioctl we lock first the mutex qgroup_ioctl_lock and then start a transaction, and starting a transaction acquires a fs freeze semaphore (at the VFS level). However, every other code path, except for the quota disable ioctl path, we do the opposite: we start a transaction and then lock the mutex. So fix this by making the quota enable and disable paths to start the transaction without having the mutex locked, and then, after starting the transaction, lock the mutex and check if some other task already enabled or disabled the quotas, bailing with success if that was the case. Signed-off-by:Filipe Manana <fdmanana@suse.com> Reviewed-by:
David Sterba <dsterba@suse.com> Signed-off-by:
David Sterba <dsterba@suse.com> Signed-off-by:
Sasha Levin <sashal@kernel.org>
parent
a70b2496
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