Fix driver new_id sysfs-attribute removal deadlock by making sure to not hold any locks that the attribute operations grab when removing the attribute.
Specifically, usb_serial_deregister holds the table mutex when deregistering the driver, which includes removing the new_id attribute. This can lead to a deadlock as writing to new_id increments the attribute's active count before trying to grab the same mutex in usb_serial_probe. The deadlock can easily be triggered by inserting a sleep in usb_serial_deregister and writing the id of an unbound device to new_id during module unload. As the table mutex (in this case) is used to prevent subdriver unload during probe, it should be sufficient to only hold the lock while manipulating the usb-serial driver list during deregister. A racing probe will then either fail to find a matching subdriver or fail to get the corresponding module reference. Since v3.15-rc1 this also triggers the following lockdep warning: ====================================================== [ INFO: possible circular locking dependency detected ] 3.15.0-rc2 #123 Tainted: G W ------------------------------------------------------- modprobe/190 is trying to acquire lock: (s_active#4){++++.+}, at: [<c0167aa0>] kernfs_remove_by_name_ns+0x4c/0x94 but task is already holding lock: (table_lock){+.+.+.}, at: [<bf004d84>] usb_serial_deregister+0x3c/0x78 [usbserial] which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (table_lock){+.+.+.}: [<c0075f84>] __lock_acquire+0x1694/0x1ce4 [<c0076de8>] lock_acquire+0xb4/0x154 [<c03af3cc>] _raw_spin_lock+0x4c/0x5c [<c02bbc24>] usb_store_new_id+0x14c/0x1ac [<bf007eb4>] new_id_store+0x68/0x70 [usbserial] [<c025f568>] drv_attr_store+0x30/0x3c [<c01690e0>] sysfs_kf_write+0x5c/0x60 [<c01682c0>] kernfs_fop_write+0xd4/0x194 [<c010881c>] vfs_write+0xbc/0x198 [<c0108e4c>] SyS_write+0x4c/0xa0 [<c000f880>] ret_fast_syscall+0x0/0x48 -> #0 (s_active#4){++++.+}: [<c03a7a28>] print_circular_bug+0x68/0x2f8 [<c0076218>] __lock_acquire+0x1928/0x1ce4 [<c0076de8>] lock_acquire+0xb4/0x154 [<c0166b70>] __kernfs_remove+0x254/0x310 [<c0167aa0>] kernfs_remove_by_name_ns+0x4c/0x94 [<c0169fb8>] remove_files.isra.1+0x48/0x84 [<c016a2fc>] sysfs_remove_group+0x58/0xac [<c016a414>] sysfs_remove_groups+0x34/0x44 [<c02623b8>] driver_remove_groups+0x1c/0x20 [<c0260e9c>] bus_remove_driver+0x3c/0xe4 [<c026235c>] driver_unregister+0x38/0x58 [<bf007fb4>] usb_serial_bus_deregister+0x84/0x88 [usbserial] [<bf004db4>] usb_serial_deregister+0x6c/0x78 [usbserial] [<bf005330>] usb_serial_deregister_drivers+0x2c/0x4c [usbserial] [<bf016618>] usb_serial_module_exit+0x14/0x1c [sierra] [<c009d6cc>] SyS_delete_module+0x184/0x210 [<c000f880>] ret_fast_syscall+0x0/0x48 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(table_lock); lock(s_active#4); lock(table_lock); lock(s_active#4); *** DEADLOCK *** 1 lock held by modprobe/190: #0: (table_lock){+.+.+.}, at: [<bf004d84>] usb_serial_deregister+0x3c/0x78 [usbserial] stack backtrace: CPU: 0 PID: 190 Comm: modprobe Tainted: G W 3.15.0-rc2 #123 [<c0015e10>] (unwind_backtrace) from [<c0013728>] (show_stack+0x20/0x24) [<c0013728>] (show_stack) from [<c03a9a54>] (dump_stack+0x24/0x28) [<c03a9a54>] (dump_stack) from [<c03a7cac>] (print_circular_bug+0x2ec/0x2f8) [<c03a7cac>] (print_circular_bug) from [<c0076218>] (__lock_acquire+0x1928/0x1ce4) [<c0076218>] (__lock_acquire) from [<c0076de8>] (lock_acquire+0xb4/0x154) [<c0076de8>] (lock_acquire) from [<c0166b70>] (__kernfs_remove+0x254/0x310) [<c0166b70>] (__kernfs_remove) from [<c0167aa0>] (kernfs_remove_by_name_ns+0x4c/0x94) [<c0167aa0>] (kernfs_remove_by_name_ns) from [<c0169fb8>] (remove_files.isra.1+0x48/0x84) [<c0169fb8>] (remove_files.isra.1) from [<c016a2fc>] (sysfs_remove_group+0x58/0xac) [<c016a2fc>] (sysfs_remove_group) from [<c016a414>] (sysfs_remove_groups+0x34/0x44) [<c016a414>] (sysfs_remove_groups) from [<c02623b8>] (driver_remove_groups+0x1c/0x20) [<c02623b8>] (driver_remove_groups) from [<c0260e9c>] (bus_remove_driver+0x3c/0xe4) [<c0260e9c>] (bus_remove_driver) from [<c026235c>] (driver_unregister+0x38/0x58) [<c026235c>] (driver_unregister) from [<bf007fb4>] (usb_serial_bus_deregister+0x84/0x88 [usbserial]) [<bf007fb4>] (usb_serial_bus_deregister [usbserial]) from [<bf004db4>] (usb_serial_deregister+0x6c/0x78 [usbserial]) [<bf004db4>] (usb_serial_deregister [usbserial]) from [<bf005330>] (usb_serial_deregister_drivers+0x2c/0x4c [usbserial]) [<bf005330>] (usb_serial_deregister_drivers [usbserial]) from [<bf016618>] (usb_serial_module_exit+0x14/0x1c [sierra]) [<bf016618>] (usb_serial_module_exit [sierra]) from [<c009d6cc>] (SyS_delete_module+0x184/0x210) [<c009d6cc>] (SyS_delete_module) from [<c000f880>] (ret_fast_syscall+0x0/0x48) Signed-off-by: Johan Hovold <jhov...@gmail.com> --- I got this new lockdep warning with 3.15-rc, but this dates back to at least 0daeed381c6a ("USB-BKL: Remove BKL use for usb serial driver probing"). As far as I can tell, moving driver deregistration out of the table lock should be fine. Another option would be to get a module reference in new_id store, although that would still trigger the lockdep warning. Thanks, Johan drivers/usb/serial/usb-serial.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c index 81fc0dfcfdcf..6d40d56378d7 100644 --- a/drivers/usb/serial/usb-serial.c +++ b/drivers/usb/serial/usb-serial.c @@ -1347,10 +1347,12 @@ static int usb_serial_register(struct usb_serial_driver *driver) static void usb_serial_deregister(struct usb_serial_driver *device) { pr_info("USB Serial deregistering driver %s\n", device->description); + mutex_lock(&table_lock); list_del(&device->driver_list); - usb_serial_bus_deregister(device); mutex_unlock(&table_lock); + + usb_serial_bus_deregister(device); } /** -- 1.8.3.2 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html