Re: [PATCH] usb: gadget: f_fs: Fix possibe deadlock

[Michal Nazarewicz]

On Thu, Dec 08 2016, Baolin Wang wrote:
> When system try to close /dev/usb-ffs/adb/ep0 on one core, at the same
> time another core try to attach new UDC, which will cause deadlock as
> below scenario. Thus we should release ffs lock before issuing
> unregister_gadget_item().
>
> [   52.642225] c1 ======================================================
> [   52.642228] c1 [ INFO: possible circular locking dependency detected ]
> [   52.642236] c1 4.4.6+ #1 Tainted: G        W  O
> [   52.642241] c1 -------------------------------------------------------
> [   52.642245] c1 usb ffs open/2808 is trying to acquire lock:
> [   52.642270] c0  (udc_lock){+.+.+.}, at: [<ffffffc00065aeec>]
> 		usb_gadget_unregister_driver+0x3c/0xc8
> [   52.642272] c1  but task is already holding lock:
> [   52.642283] c0  (ffs_lock){+.+.+.}, at: [<ffffffc00066b244>]
> 		ffs_data_clear+0x30/0x140
> [   52.642285] c1 which lock already depends on the new lock.
> [   52.642287] c1
>                the existing dependency chain (in reverse order) is:
> [   52.642295] c0
> 	       -> #1 (ffs_lock){+.+.+.}:
> [   52.642307] c0        [<ffffffc00012340c>] __lock_acquire+0x20f0/0x2238
> [   52.642314] c0        [<ffffffc000123b54>] lock_acquire+0xe4/0x298
> [   52.642322] c0        [<ffffffc000aaf6e8>] mutex_lock_nested+0x7c/0x3cc
> [   52.642328] c0        [<ffffffc00066f7bc>] ffs_func_bind+0x504/0x6e8
> [   52.642334] c0        [<ffffffc000654004>] usb_add_function+0x84/0x184
> [   52.642340] c0        [<ffffffc000658ca4>] configfs_composite_bind+0x264/0x39c
> [   52.642346] c0        [<ffffffc00065b348>] udc_bind_to_driver+0x58/0x11c
> [   52.642352] c0        [<ffffffc00065b49c>] usb_udc_attach_driver+0x90/0xc8
> [   52.642358] c0        [<ffffffc0006598e0>] gadget_dev_desc_UDC_store+0xd4/0x128
> [   52.642369] c0        [<ffffffc0002c14e8>] configfs_write_file+0xd0/0x13c
> [   52.642376] c0        [<ffffffc00023c054>] vfs_write+0xb8/0x214
> [   52.642381] c0        [<ffffffc00023cad4>] SyS_write+0x54/0xb0
> [   52.642388] c0        [<ffffffc000085ff0>] el0_svc_naked+0x24/0x28
> [   52.642395] c0
>               -> #0 (udc_lock){+.+.+.}:
> [   52.642401] c0        [<ffffffc00011e3d0>] print_circular_bug+0x84/0x2e4
> [   52.642407] c0        [<ffffffc000123454>] __lock_acquire+0x2138/0x2238
> [   52.642412] c0        [<ffffffc000123b54>] lock_acquire+0xe4/0x298
> [   52.642420] c0        [<ffffffc000aaf6e8>] mutex_lock_nested+0x7c/0x3cc
> [   52.642427] c0        [<ffffffc00065aeec>] usb_gadget_unregister_driver+0x3c/0xc8
> [   52.642432] c0        [<ffffffc00065995c>] unregister_gadget_item+0x28/0x44
> [   52.642439] c0        [<ffffffc00066b34c>] ffs_data_clear+0x138/0x140
> [   52.642444] c0        [<ffffffc00066b374>] ffs_data_reset+0x20/0x6c
> [   52.642450] c0        [<ffffffc00066efd0>] ffs_data_closed+0xac/0x12c
> [   52.642454] c0        [<ffffffc00066f070>] ffs_ep0_release+0x20/0x2c
> [   52.642460] c0        [<ffffffc00023dbe4>] __fput+0xb0/0x1f4
> [   52.642466] c0        [<ffffffc00023dd9c>] ____fput+0x20/0x2c
> [   52.642473] c0        [<ffffffc0000ee944>] task_work_run+0xb4/0xe8
> [   52.642482] c0        [<ffffffc0000cd45c>] do_exit+0x360/0xb9c
> [   52.642487] c0        [<ffffffc0000cf228>] do_group_exit+0x4c/0xb0
> [   52.642494] c0        [<ffffffc0000dd3c8>] get_signal+0x380/0x89c
> [   52.642501] c0        [<ffffffc00008a8f0>] do_signal+0x154/0x518
> [   52.642507] c0        [<ffffffc00008af00>] do_notify_resume+0x70/0x78
> [   52.642512] c0        [<ffffffc000085ee8>] work_pending+0x1c/0x20
> [   52.642514] c1
>               other info that might help us debug this:
> [   52.642517] c1  Possible unsafe locking scenario:
> [   52.642518] c1        CPU0                    CPU1
> [   52.642520] c1        ----                    ----
> [   52.642525] c0   lock(ffs_lock);
> [   52.642529] c0                                lock(udc_lock);
> [   52.642533] c0                                lock(ffs_lock);
> [   52.642537] c0   lock(udc_lock);
> [   52.642539] c1
>                       *** DEADLOCK ***
> [   52.642543] c1 1 lock held by usb ffs open/2808:
> [   52.642555] c0  #0:  (ffs_lock){+.+.+.}, at: [<ffffffc00066b244>]
> 		ffs_data_clear+0x30/0x140
> [   52.642557] c1 stack backtrace:
> [   52.642563] c1 CPU: 1 PID: 2808 Comm: usb ffs open Tainted: G
> [   52.642565] c1 Hardware name: Spreadtrum SP9860g Board (DT)
> [   52.642568] c1 Call trace:
> [   52.642573] c1 [<ffffffc00008b430>] dump_backtrace+0x0/0x170
> [   52.642577] c1 [<ffffffc00008b5c0>] show_stack+0x20/0x28
> [   52.642583] c1 [<ffffffc000422694>] dump_stack+0xa8/0xe0
> [   52.642587] c1 [<ffffffc00011e548>] print_circular_bug+0x1fc/0x2e4
> [   52.642591] c1 [<ffffffc000123454>] __lock_acquire+0x2138/0x2238
> [   52.642595] c1 [<ffffffc000123b54>] lock_acquire+0xe4/0x298
> [   52.642599] c1 [<ffffffc000aaf6e8>] mutex_lock_nested+0x7c/0x3cc
> [   52.642604] c1 [<ffffffc00065aeec>] usb_gadget_unregister_driver+0x3c/0xc8
> [   52.642608] c1 [<ffffffc00065995c>] unregister_gadget_item+0x28/0x44
> [   52.642613] c1 [<ffffffc00066b34c>] ffs_data_clear+0x138/0x140
> [   52.642618] c1 [<ffffffc00066b374>] ffs_data_reset+0x20/0x6c
> [   52.642621] c1 [<ffffffc00066efd0>] ffs_data_closed+0xac/0x12c
> [   52.642625] c1 [<ffffffc00066f070>] ffs_ep0_release+0x20/0x2c
> [   52.642629] c1 [<ffffffc00023dbe4>] __fput+0xb0/0x1f4
> [   52.642633] c1 [<ffffffc00023dd9c>] ____fput+0x20/0x2c
> [   52.642636] c1 [<ffffffc0000ee944>] task_work_run+0xb4/0xe8
> [   52.642640] c1 [<ffffffc0000cd45c>] do_exit+0x360/0xb9c
> [   52.642644] c1 [<ffffffc0000cf228>] do_group_exit+0x4c/0xb0
> [   52.642647] c1 [<ffffffc0000dd3c8>] get_signal+0x380/0x89c
> [   52.642651] c1 [<ffffffc00008a8f0>] do_signal+0x154/0x518
> [   52.642656] c1 [<ffffffc00008af00>] do_notify_resume+0x70/0x78
> [   52.642659] c1 [<ffffffc000085ee8>] work_pending+0x1c/0x20
>
> Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxx>

Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>

> ---
>  drivers/usb/gadget/function/f_fs.c |    8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index 0780d83..93de3b9 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -3666,6 +3666,7 @@ static void ffs_closed(struct ffs_data *ffs)
>  {
>  	struct ffs_dev *ffs_obj;
>  	struct f_fs_opts *opts;
> +	struct config_item *ci;
>  
>  	ENTER();
>  	ffs_dev_lock();
> @@ -3689,8 +3690,11 @@ static void ffs_closed(struct ffs_data *ffs)
>  	    || !atomic_read(&opts->func_inst.group.cg_item.ci_kref.refcount))
>  		goto done;
>  
> -	unregister_gadget_item(ffs_obj->opts->
> -			       func_inst.group.cg_item.ci_parent->ci_parent);
> +	ci = opts->func_inst.group.cg_item.ci_parent->ci_parent;
> +	ffs_dev_unlock();
> +
> +	unregister_gadget_item(ci);
> +	return;
>  done:
>  	ffs_dev_unlock();
>  }
> -- 
> 1.7.9.5
>

-- 
Best regards
ããã âðððð86â ãããããã
ÂIf at first you donât succeed, give up skydivingÂ