[PATCH 4.5 113/128] btrfs: fix lock dep warning, move scratch dev out of device_list_mutex and uuid_mutex

Greg Kroah-Hartman
2016-06-06T14:38:55Z

From: Anand Jain <anand.jain@oracle.com>

commit 779bf3fefa835cb52a07457c8acac6f2f66f2493 upstream.

When the replace target fails, the target device will be taken
out of fs device list, scratch + update_dev_time and freed. However
we could do the scratch + update_dev_time and free part after the
device has been taken out of device list, so that we don't have to
hold the device_list_mutex and uuid_mutex locks.

Reported issue:

[ 5375.718845] ======================================================
[ 5375.718846] [ INFO: possible circular locking dependency detected ]
[ 5375.718849] 4.4.5-scst31x-debug-11+ #40 Not tainted
[ 5375.718849] -------------------------------------------------------
[ 5375.718851] btrfs-health/4662 is trying to acquire lock:
[ 5375.718861] (sb_writers){.+.+.+}, at: [<ffffffff812214f7>] __sb_start_write+0xb7/0xf0
[ 5375.718862]
[ 5375.718862] but task is already holding lock:
[ 5375.718907] (&fs_devs->device_list_mutex){+.+.+.}, at: [<ffffffffa028263c>] btrfs_destroy_dev_replace_tgtdev+0x3c/0x150 [btrfs]
[ 5375.718907]
[ 5375.718907] which lock already depends on the new lock.
[ 5375.718907]
[ 5375.718908]
[ 5375.718908] the existing dependency chain (in reverse order) is:
[ 5375.718911]
[ 5375.718911] -> #3 (&fs_devs->device_list_mutex){+.+.+.}:
[ 5375.718917] [<ffffffff810da4be>] lock_acquire+0xce/0x1e0
[ 5375.718921] [<ffffffff81633949>] mutex_lock_nested+0x69/0x3c0
[ 5375.718940] [<ffffffffa0219bf6>] btrfs_show_devname+0x36/0x210 [btrfs]
[ 5375.718945] [<ffffffff81267079>] show_vfsmnt+0x49/0x150
[ 5375.718948] [<ffffffff81240b07>] m_show+0x17/0x20
[ 5375.718951] [<ffffffff81246868>] seq_read+0x2d8/0x3b0
[ 5375.718955] [<ffffffff8121df28>] __vfs_read+0x28/0xd0
[ 5375.718959] [<ffffffff8121e806>] vfs_read+0x86/0x130
[ 5375.718962] [<ffffffff8121f4c9>] SyS_read+0x49/0xa0
[ 5375.718966] [<ffffffff81637976>] entry_SYSCALL_64_fastpath+0x16/0x7a
[ 5375.718968]
[ 5375.718968] -> #2 (namespace_sem){+++++.}:
[ 5375.718971] [<ffffffff810da4be>] lock_acquire+0xce/0x1e0
[ 5375.718974] [<ffffffff81635199>] down_write+0x49/0x80
[ 5375.718977] [<ffffffff81243593>] lock_mount+0x43/0x1c0
[ 5375.718979] [<ffffffff81243c13>] do_add_mount+0x23/0xd0
[ 5375.718982] [<ffffffff81244afb>] do_mount+0x27b/0xe30
[ 5375.718985] [<ffffffff812459dc>] SyS_mount+0x8c/0xd0
[ 5375.718988] [<ffffffff81637976>] entry_SYSCALL_64_fastpath+0x16/0x7a
[ 5375.718991]
[ 5375.718991] -> #1 (&sb->s_type->i_mutex_key#5){+.+.+.}:
[ 5375.718994] [<ffffffff810da4be>] lock_acquire+0xce/0x1e0
[ 5375.718996] [<ffffffff81633949>] mutex_lock_nested+0x69/0x3c0
[ 5375.719001] [<ffffffff8122d608>] path_openat+0x468/0x1360
[ 5375.719004] [<ffffffff8122f86e>] do_filp_open+0x7e/0xe0
[ 5375.719007] [<ffffffff8121da7b>] do_sys_open+0x12b/0x210
[ 5375.719010] [<ffffffff8121db7e>] SyS_open+0x1e/0x20
[ 5375.719013] [<ffffffff81637976>] entry_SYSCALL_64_fastpath+0x16/0x7a
[ 5375.719015]
[ 5375.719015] -> #0 (sb_writers){.+.+.+}:
[ 5375.719018] [<ffffffff810d97ca>] __lock_acquire+0x17ba/0x1ae0
[ 5375.719021] [<ffffffff810da4be>] lock_acquire+0xce/0x1e0
[ 5375.719026] [<ffffffff810d3bef>] percpu_down_read+0x4f/0xa0
[ 5375.719028] [<ffffffff812214f7>] __sb_start_write+0xb7/0xf0
[ 5375.719031] [<ffffffff81242eb4>] mnt_want_write+0x24/0x50
[ 5375.719035] [<ffffffff8122ded2>] path_openat+0xd32/0x1360
[ 5375.719037] [<ffffffff8122f86e>] do_filp_open+0x7e/0xe0
[ 5375.719040] [<ffffffff8121d8a4>] file_open_name+0xe4/0x130
[ 5375.719043] [<ffffffff8121d923>] filp_open+0x33/0x60
[ 5375.719073] [<ffffffffa02776a6>] update_dev_time+0x16/0x40 [btrfs]
[ 5375.719099] [<ffffffffa02825be>] btrfs_scratch_superblocks+0x4e/0x90 [btrfs]
[ 5375.719123] [<ffffffffa0282665>] btrfs_destroy_dev_replace_tgtdev+0x65/0x150 [btrfs]
[ 5375.719150] [<ffffffffa02c6c80>] btrfs_dev_replace_finishing+0x6b0/0x990 [btrfs]
[ 5375.719175] [<ffffffffa02c729e>] btrfs_dev_replace_start+0x33e/0x540 [btrfs]
[ 5375.719199] [<ffffffffa02c7f58>] btrfs_auto_replace_start+0xf8/0x140 [btrfs]
[ 5375.719222] [<ffffffffa02464e6>] health_kthread+0x246/0x490 [btrfs]
[ 5375.719225] [<ffffffff810a70df>] kthread+0xef/0x110
[ 5375.719229] [<ffffffff81637d2f>] ret_from_fork+0x3f/0x70
[ 5375.719230]
[ 5375.719230] other info that might help us debug this:
[ 5375.719230]
[ 5375.719233] Chain exists of:
[ 5375.719233] sb_writers --> namespace_sem --> &fs_devs->device_list_mutex
[ 5375.719233]
[ 5375.719234] Possible unsafe locking scenario:
[ 5375.719234]
[ 5375.719234] CPU0 CPU1
[ 5375.719235] ---- ----
[ 5375.719236] lock(&fs_devs->device_list_mutex);
[ 5375.719238] lock(namespace_sem);
[ 5375.719239] lock(&fs_devs->device_list_mutex);
[ 5375.719241] lock(sb_writers);
[ 5375.719241]
[ 5375.719241] *** DEADLOCK ***
[ 5375.719241]
[ 5375.719243] 4 locks held by btrfs-health/4662:
[ 5375.719266] #0: (&fs_info->health_mutex){+.+.+.}, at: [<ffffffffa0246303>] health_kthread+0x63/0x490 [btrfs]
[ 5375.719293] #1: (&fs_info->dev_replace.lock_finishing_cancel_unmount){+.+.+.}, at: [<ffffffffa02c6611>] btrfs_dev_replace_finishing+0x41/0x990 [btrfs]
[ 5375.719319] #2: (uuid_mutex){+.+.+.}, at: [<ffffffffa0282620>] btrfs_destroy_dev_replace_tgtdev+0x20/0x150 [btrfs]
[ 5375.719343] #3: (&fs_devs->device_list_mutex){+.+.+.}, at: [<ffffffffa028263c>] btrfs_destroy_dev_replace_tgtdev+0x3c/0x150 [btrfs]
[ 5375.719343]
[ 5375.719343] stack backtrace:
[ 5375.719347] CPU: 2 PID: 4662 Comm: btrfs-health Not tainted 4.4.5-scst31x-debug-11+ #40
[ 5375.719348] Hardware name: Supermicro SYS-6018R-WTRT/X10DRW-iT, BIOS 1.0c 01/07/2015
[ 5375.719352] 0000000000000000 ffff880856f73880 ffffffff813529e3 ffffffff826182a0
[ 5375.719354] ffffffff8260c090 ffff880856f738c0 ffffffff810d667c ffff880856f73930
[ 5375.719357] ffff880861f32b40 ffff880861f32b68 0000000000000003 0000000000000004
[ 5375.719357] Call Trace:
[ 5375.719363] [<ffffffff813529e3>] dump_stack+0x85/0xc2
[ 5375.719366] [<ffffffff810d667c>] print_circular_bug+0x1ec/0x260
[ 5375.719369] [<ffffffff810d97ca>] __lock_acquire+0x17ba/0x1ae0
[ 5375.719373] [<ffffffff810f606d>] ? debug_lockdep_rcu_enabled+0x1d/0x20
[ 5375.719376] [<ffffffff810da4be>] lock_acquire+0xce/0x1e0
[ 5375.719378] [<ffffffff812214f7>] ? __sb_start_write+0xb7/0xf0
[ 5375.719383] [<ffffffff810d3bef>] percpu_down_read+0x4f/0xa0
[ 5375.719385] [<ffffffff812214f7>] ? __sb_start_write+0xb7/0xf0
[ 5375.719387] [<ffffffff812214f7>] __sb_start_write+0xb7/0xf0
[ 5375.719389] [<ffffffff81242eb4>] mnt_want_write+0x24/0x50
[ 5375.719393] [<ffffffff8122ded2>] path_openat+0xd32/0x1360
[ 5375.719415] [<ffffffffa02462a0>] ? btrfs_congested_fn+0x180/0x180 [btrfs]
[ 5375.719418] [<ffffffff810f606d>] ? debug_lockdep_rcu_enabled+0x1d/0x20
[ 5375.719420] [<ffffffff8122f86e>] do_filp_open+0x7e/0xe0
[ 5375.719423] [<ffffffff810f615d>] ? rcu_read_lock_sched_held+0x6d/0x80
[ 5375.719426] [<ffffffff81201a9b>] ? kmem_cache_alloc+0x26b/0x5d0
[ 5375.719430] [<ffffffff8122e7d4>] ? getname_kernel+0x34/0x120
[ 5375.719433] [<ffffffff8121d8a4>] file_open_name+0xe4/0x130
[ 5375.719436] [<ffffffff8121d923>] filp_open+0x33/0x60
[ 5375.719462] [<ffffffffa02776a6>] update_dev_time+0x16/0x40 [btrfs]
[ 5375.719485] [<ffffffffa02825be>] btrfs_scratch_superblocks+0x4e/0x90 [btrfs]
[ 5375.719506] [<ffffffffa0282665>] btrfs_destroy_dev_replace_tgtdev+0x65/0x150 [btrfs]
[ 5375.719530] [<ffffffffa02c6c80>] btrfs_dev_replace_finishing+0x6b0/0x990 [btrfs]
[ 5375.719554] [<ffffffffa02c6b23>] ? btrfs_dev_replace_finishing+0x553/0x990 [btrfs]
[ 5375.719576] [<ffffffffa02c729e>] btrfs_dev_replace_start+0x33e/0x540 [btrfs]
[ 5375.719598] [<ffffffffa02c7f58>] btrfs_auto_replace_start+0xf8/0x140 [btrfs]
[ 5375.719621] [<ffffffffa02464e6>] health_kthread+0x246/0x490 [btrfs]
[ 5375.719641] [<ffffffffa02463d8>] ? health_kthread+0x138/0x490 [btrfs]
[ 5375.719661] [<ffffffffa02462a0>] ? btrfs_congested_fn+0x180/0x180 [btrfs]
[ 5375.719663] [<ffffffff810a70df>] kthread+0xef/0x110
[ 5375.719666] [<ffffffff810a6ff0>] ? kthread_create_on_node+0x200/0x200
[ 5375.719669] [<ffffffff81637d2f>] ret_from_fork+0x3f/0x70
[ 5375.719672] [<ffffffff810a6ff0>] ? kthread_create_on_node+0x200/0x200
[ 5375.719697] ------------[ cut here ]------------

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reported-by: Yauhen Kharuzhy <yauhen.kharuzhy@zavadatar.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/btrfs/volumes.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)

--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2023,10 +2023,9 @@ void btrfs_destroy_dev_replace_tgtdev(st

btrfs_sysfs_rm_device_link(fs_info->fs_devices, tgtdev);

- if (tgtdev->bdev) {
- btrfs_scratch_superblocks(tgtdev->bdev, tgtdev->name->str);
+ if (tgtdev->bdev)
fs_info->fs_devices->open_devices--;
- }
+
fs_info->fs_devices->num_devices--;

next_device = list_entry(fs_info->fs_devices->devices.next,
@@ -2037,10 +2036,18 @@ void btrfs_destroy_dev_replace_tgtdev(st
fs_info->fs_devices->latest_bdev = next_device->bdev;
list_del_rcu(&tgtdev->dev_list);

- call_rcu(&tgtdev->rcu, free_device);
-
mutex_unlock(&fs_info->fs_devices->device_list_mutex);
mutex_unlock(&uuid_mutex);
+
+ /*
+ * The update_dev_time() with in btrfs_scratch_superblocks()
+ * may lead to a call to btrfs_show_devname() which will try
+ * to hold device_list_mutex. And here this device
+ * is already out of device list, so we don't have to hold
+ * the device_list_mutex lock.
+ */
+ btrfs_scratch_superblocks(tgtdev->bdev, tgtdev->name->str);
+ call_rcu(&tgtdev->rcu, free_device);
}

static int btrfs_find_device_by_path(struct btrfs_root *root, char *device_path,