On Tue, 2017-05-23 at 16:48 -0700, Bart Van Assche wrote:
> Move the code for parsing an XCOPY command from the context of
> the iSCSI receiver thread to the context of the XCOPY workqueue.
> Keep the simple XCOPY checks in the context of the iSCSI receiver
> thread. Move the code for allocating and freeing struct xcopy_op
> from the code that parses an XCOPY command to its caller.
>
> This patch fixes the following deadlock:
>
> ======================================================
> [ INFO: possible circular locking dependency detected ]
> 4.10.0-rc7-dbg+ #1 Not tainted
> -------------------------------------------------------
> rmdir/13321 is trying to acquire lock:
> (&sess->cmdsn_mutex){+.+.+.}, at: [<ffffffffa02cb47d>] iscsit_free_all_ooo_cmdsns+0x2d/0xb0 [iscsi_target_mod]
>
> but task is already holding lock:
> (&sb->s_type->i_mutex_key#14){++++++}, at: [<ffffffff811c6e20>] 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+0x71/0x90
> down_write+0x3f/0x70
> configfs_depend_item+0x3a/0xb0 [configfs]
> target_depend_item+0x13/0x20 [target_core_mod]
> target_xcopy_locate_se_dev_e4+0xdd/0x1a0 [target_core_mod]
> target_do_xcopy+0x34b/0x970 [target_core_mod]
> __target_execute_cmd+0x22/0xa0 [target_core_mod]
> target_execute_cmd+0x233/0x2c0 [target_core_mod]
> iscsit_execute_cmd+0x208/0x270 [iscsi_target_mod]
> iscsit_sequence_cmd+0x10b/0x190 [iscsi_target_mod]
> iscsit_get_rx_pdu+0x37d/0xcd0 [iscsi_target_mod]
> iscsi_target_rx_thread+0x6e/0xa0 [iscsi_target_mod]
> kthread+0x102/0x140
> ret_from_fork+0x31/0x40
>
> -> #0 (&sess->cmdsn_mutex){+.+.+.}:
> __lock_acquire+0x10e6/0x1260
> lock_acquire+0x71/0x90
> mutex_lock_nested+0x5f/0x670
> iscsit_free_all_ooo_cmdsns+0x2d/0xb0 [iscsi_target_mod]
> iscsit_close_session+0xac/0x200 [iscsi_target_mod]
> lio_tpg_close_session+0x9f/0xb0 [iscsi_target_mod]
> target_shutdown_sessions+0xc3/0xd0 [target_core_mod]
> core_tpg_del_initiator_node_acl+0x91/0x140 [target_core_mod]
> target_fabric_nacl_base_release+0x20/0x30 [target_core_mod]
> config_item_release+0x5a/0xc0 [configfs]
> config_item_put+0x1d/0x1f [configfs]
> configfs_rmdir+0x1a6/0x300 [configfs]
> vfs_rmdir+0xb7/0x140
> do_rmdir+0x1f4/0x200
> SyS_rmdir+0x11/0x20
> entry_SYSCALL_64_fastpath+0x23/0xc6
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
> CPU0 CPU1
> ---- ----
> lock(&sb->s_type->i_mutex_key#14);
> lock(&sess->cmdsn_mutex);
> lock(&sb->s_type->i_mutex_key#14);
> lock(&sess->cmdsn_mutex);
>
> *** DEADLOCK ***
>
> 3 locks held by rmdir/13321:
> #0: (sb_writers#10){.+.+.+}, at: [<ffffffff811e1aff>] mnt_want_write+0x1f/0x50
> #1: (&default_group_class[depth - 1]#2/1){+.+.+.}, at: [<ffffffff811cc8ce>] do_rmdir+0x15e/0x200
> #2: (&sb->s_type->i_mutex_key#14){++++++}, at: [<ffffffff811c6e20>] vfs_rmdir+0x50/0x140
>
> stack backtrace:
> CPU: 2 PID: 13321 Comm: rmdir Not tainted 4.10.0-rc7-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+0x86/0xc3
> print_circular_bug+0x1c7/0x220
> __lock_acquire+0x10e6/0x1260
> lock_acquire+0x71/0x90
> mutex_lock_nested+0x5f/0x670
> iscsit_free_all_ooo_cmdsns+0x2d/0xb0 [iscsi_target_mod]
> iscsit_close_session+0xac/0x200 [iscsi_target_mod]
> lio_tpg_close_session+0x9f/0xb0 [iscsi_target_mod]
> target_shutdown_sessions+0xc3/0xd0 [target_core_mod]
> core_tpg_del_initiator_node_acl+0x91/0x140 [target_core_mod]
> target_fabric_nacl_base_release+0x20/0x30 [target_core_mod]
> config_item_release+0x5a/0xc0 [configfs]
> config_item_put+0x1d/0x1f [configfs]
> configfs_rmdir+0x1a6/0x300 [configfs]
> vfs_rmdir+0xb7/0x140
> do_rmdir+0x1f4/0x200
> SyS_rmdir+0x11/0x20
> entry_SYSCALL_64_fastpath+0x23/0xc6
>
> Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Andy Grover <agrover@xxxxxxxxxx>
> Cc: David Disseldorp <ddiss@xxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> ---
> drivers/target/target_core_xcopy.c | 110 +++++++++++++++++++++++--------------
> 1 file changed, 69 insertions(+), 41 deletions(-)
Applied, but dropping the stable CC'.
In practice this deadlock has never triggered, so it's not stable
material.