On 09/01/2017 12:37 PM, Bart Van Assche wrote:
> 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;
>
Oh wow, I messed up. I wonder how I did not see that, because I had
tested those other patches with lock dep on so its enabled. Thanks!
Reviewed-by: Mike Christie <mchristi@xxxxxxxxxx>
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