On Tue, Mar 29, 2016 at 10:40:40PM +0300, Yauhen Kharuzhy wrote:
> Hi.
>
> I am testing hotspare v2 on kernel v4.4.5 (I will try latest Chris' tree later)
> now with lockdep debugging enabled. At starting of replacement, lockdep warning is displayed,
> because kstrdup() is called with GFP_NOFS inside of rcu_read_lock/unlock()
> block (GFP_NOFS can sleep).
Similar thing in the btrfs_auto_replace_start(): rcu_str_deref() without
rcu_read_lock():
int btrfs_auto_replace_start(struct btrfs_root *root,
struct btrfs_device *src_device)
{
int ret;
char *tgt_path;
if (btrfs_get_spare_device(&tgt_path)) {
btrfs_err(root->fs_info,
"No spare device found/configured in the kernel");
return -EINVAL;
}
ret = btrfs_dev_replace_start(root, tgt_path,
src_device->devid,
rcu_str_deref(src_device->name),
BTRFS_IOCTL_DEV_REPLACE_CONT_READING_FROM_SRCDEV_MODE_AVOID);
if (ret)
btrfs_put_spare_device(tgt_path);
kfree(tgt_path);
return 0;
}
[ 156.168133] ===============================
[ 156.168963] [ INFO: suspicious RCU usage. ]
[ 156.169822] 4.4.5-scst31x+ #20 Not tainted
[ 156.170656] -------------------------------
[ 156.171488] fs/btrfs/dev-replace.c:990 suspicious rcu_dereference_check() usage!
[ 156.172920]
[ 156.172920] other info that might help us debug this:
[ 156.172920]
[ 156.174825]
[ 156.174825] rcu_scheduler_active = 1, debug_locks = 0
[ 156.176152] 1 lock held by btrfs-casualty/4807:
[ 156.181917] #0: (&fs_info->casualty_mutex){+.+...}, at: [<ffffffffa0165364>] casualty_kthread+0x64/0x390 [btrfs]
[ 156.193511]
[ 156.193511] stack backtrace:
[ 156.194680] CPU: 0 PID: 4807 Comm: btrfs-casualty Not tainted 4.4.5-scst31x+ #20
[ 156.201650] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[ 156.219100] 0000000000000000 ffff88005d79fda0 ffffffff813529e3 ffff88005e19c600
[ 156.221216] 0000000000000001 ffff88005d79fdd0 ffffffff810d6407 0000000000000000
[ 156.224287] 0000000000000000 ffff88005f4a0c00 ffff88005da36000 ffff88005d79fe08
[ 156.226375] Call Trace:
[ 156.227078] [<ffffffff813529e3>] dump_stack+0x85/0xc2
[ 156.228152] [<ffffffff810d6407>] lockdep_rcu_suspicious+0xd7/0x110
[ 156.229418] [<ffffffffa01e6236>] btrfs_auto_replace_start+0xa6/0xd0 [btrfs]
[ 156.230714] [<ffffffffa01655c4>] casualty_kthread+0x2c4/0x390 [btrfs]
[ 156.231915] [<ffffffffa016549c>] ? casualty_kthread+0x19c/0x390 [btrfs]
[ 156.233105] [<ffffffffa0165300>] ? btrfs_check_devices+0x200/0x200 [btrfs]
[ 156.234339] [<ffffffff810a70df>] kthread+0xef/0x110
[ 156.235309] [<ffffffff810dc081>] ? __raw_callee_save___pv_queued_spin_unlock+0x11/0x20
[ 156.236940] [<ffffffff810a6ff0>] ? kthread_create_on_node+0x200/0x200
[ 156.239489] [<ffffffff81637c2f>] ret_from_fork+0x3f/0x70
[ 156.240533] [<ffffffff810a6ff0>] ? kthread_create_on_node+0x200/0x200
--
Yauhen Kharuzhy
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