This patch prevents that lockdep reports the following complaint:
======================================================
WARNING: possible circular locking dependency detected
4.12.0-rc1-dbg+ #1 Not tainted
------------------------------------------------------
rmdir/12053 is trying to acquire lock:
(device_mutex#2){+.+.+.}, at: [<ffffffffa010afce>] target_free_device+0xae/0xf0 [target_core_mod]
but task is already holding lock:
(&sb->s_type->i_mutex_key#14){++++++}, at: [<ffffffff811c5c30>] vfs_rmdir+0x50/0x140
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&sb->s_type->i_mutex_key#14){++++++}:
lock_acquire+0x59/0x80
down_write+0x36/0x70
configfs_depend_item+0x3a/0xb0 [configfs]
target_depend_item+0x13/0x20 [target_core_mod]
target_xcopy_locate_se_dev_e4_iter+0x87/0x100 [target_core_mod]
target_devices_idr_iter+0x16/0x20 [target_core_mod]
idr_for_each+0x39/0xc0
target_for_each_device+0x36/0x50 [target_core_mod]
target_xcopy_locate_se_dev_e4+0x28/0x80 [target_core_mod]
target_xcopy_do_work+0x2e9/0xdd0 [target_core_mod]
process_one_work+0x1ca/0x3f0
worker_thread+0x49/0x3b0
kthread+0x109/0x140
ret_from_fork+0x31/0x40
-> #0 (device_mutex#2){+.+.+.}:
__lock_acquire+0x101f/0x11d0
lock_acquire+0x59/0x80
__mutex_lock+0x7e/0x950
mutex_lock_nested+0x16/0x20
target_free_device+0xae/0xf0 [target_core_mod]
target_core_dev_release+0x10/0x20 [target_core_mod]
config_item_put+0x6e/0xb0 [configfs]
configfs_rmdir+0x1a6/0x300 [configfs]
vfs_rmdir+0xb7/0x140
do_rmdir+0x1f4/0x200
SyS_rmdir+0x11/0x20
entry_SYSCALL_64_fastpath+0x23/0xc2
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&sb->s_type->i_mutex_key#14);
lock(device_mutex#2);
lock(&sb->s_type->i_mutex_key#14);
lock(device_mutex#2);
*** DEADLOCK ***
3 locks held by rmdir/12053:
#0: (sb_writers#10){.+.+.+}, at: [<ffffffff811e223f>] mnt_want_write+0x1f/0x50
#1: (&sb->s_type->i_mutex_key#14/1){+.+.+.}, at: [<ffffffff811cb97e>] do_rmdir+0x15e/0x200
#2: (&sb->s_type->i_mutex_key#14){++++++}, at: [<ffffffff811c5c30>] vfs_rmdir+0x50/0x140
stack backtrace:
CPU: 3 PID: 12053 Comm: rmdir Not tainted 4.12.0-rc1-dbg+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
Call Trace:
dump_stack+0x86/0xcf
print_circular_bug+0x1c7/0x220
__lock_acquire+0x101f/0x11d0
lock_acquire+0x59/0x80
__mutex_lock+0x7e/0x950
mutex_lock_nested+0x16/0x20
target_free_device+0xae/0xf0 [target_core_mod]
target_core_dev_release+0x10/0x20 [target_core_mod]
config_item_put+0x6e/0xb0 [configfs]
configfs_rmdir+0x1a6/0x300 [configfs]
vfs_rmdir+0xb7/0x140
do_rmdir+0x1f4/0x200
SyS_rmdir+0x11/0x20
entry_SYSCALL_64_fastpath+0x23/0xc2
Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Mike Christie <mchristi@xxxxxxxxxx>
---
drivers/target/target_core_configfs.c | 18 +++++++++++++++++-
include/target/target_core_base.h | 1 +
2 files changed, 18 insertions(+), 1 deletion(-)
diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c
index 7e87d952bb7a..7d0971789f12 100644
--- a/drivers/target/target_core_configfs.c
+++ b/drivers/target/target_core_configfs.c
@@ -2251,13 +2251,29 @@ static struct configfs_attribute *target_core_dev_attrs[] = {
NULL,
};
+static void target_core_dev_release_work(struct work_struct *release_work)
+{
+ struct se_device *dev =
+ container_of(release_work, struct se_device, release_work);
+
+ target_free_device(dev);
+}
+
static void target_core_dev_release(struct config_item *item)
{
struct config_group *dev_cg = to_config_group(item);
struct se_device *dev =
container_of(dev_cg, struct se_device, dev_group);
- target_free_device(dev);
+ /*
+ * Call target_free_device() asynchronously to avoid lock inversion
+ * against the configfs_depend_item() call from
+ * target_xcopy_locate_se_dev_e4_iter(). That call namely occurs with
+ * device_mutex held. This function is called from inside vfs_rmdir
+ * and hence is called with i_rwsem held.
+ */
+ INIT_WORK(&dev->release_work, target_core_dev_release_work);
+ schedule_work(&dev->release_work);
}
/*
diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 516764febeb7..19da905dd2ca 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -793,6 +793,7 @@ struct se_device {
struct list_head dev_tmr_list;
struct workqueue_struct *tmr_wq;
struct work_struct qf_work_queue;
+ struct work_struct release_work;
struct list_head delayed_cmd_list;
struct list_head state_list;
struct list_head qf_cmd_list;
--
2.14.1
