From 7e1b1fc4dabd6ec8e28baa0708866e13fa93c9b3 Mon Sep 17 00:00:00 2001 From: Jiri Slaby Date: Fri, 10 Jun 2016 10:54:32 +0200 Subject: [PATCH] base: make module_create_drivers_dir race-free Modules which register drivers via standard path (driver_register) in parallel can cause a warning: WARNING: CPU: 2 PID: 3492 at ../fs/sysfs/dir.c:31 sysfs_warn_dup+0x62/0x80 sysfs: cannot create duplicate filename '/module/saa7146/drivers' Modules linked in: hexium_gemini(+) mxb(+) ... ... Call Trace: ... [] sysfs_warn_dup+0x62/0x80 [] sysfs_create_dir_ns+0x77/0x90 [] kobject_add_internal+0xb4/0x340 [] kobject_add+0x68/0xb0 [] kobject_create_and_add+0x31/0x70 [] module_add_driver+0xc3/0xd0 [] bus_add_driver+0x154/0x280 [] driver_register+0x60/0xe0 [] __pci_register_driver+0x60/0x70 [] saa7146_register_extension+0x64/0x90 [saa7146] [] hexium_init_module+0x11/0x1000 [hexium_gemini] ... As can be (mostly) seen, driver_register causes this call sequence: -> bus_add_driver -> module_add_driver -> module_create_drivers_dir The last one creates "drivers" directory in /sys/module/<...>. When this is done in parallel, the directory is attempted to be created twice at the same time. This can be easily reproduced by loading mxb and hexium_gemini in parallel: while :; do modprobe mxb & modprobe hexium_gemini wait rmmod mxb hexium_gemini saa7146_vv saa7146 done saa7146 calls pci_register_driver for both mxb and hexium_gemini, which means /sys/module/saa7146/drivers is to be created for both of them. Fix this by a new mutex in module_create_drivers_dir which makes the test-and-create "drivers" dir atomic. I inverted the condition and removed 'return' to avoid multiple unlocks or a goto. Signed-off-by: Jiri Slaby Fixes: fe480a2675ed (Modules: only add drivers/ direcory if needed) Cc: v2.6.21+ Signed-off-by: Greg Kroah-Hartman --- drivers/base/module.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/drivers/base/module.c b/drivers/base/module.c index db930d3ee312..2a215780eda2 100644 --- a/drivers/base/module.c +++ b/drivers/base/module.c @@ -24,10 +24,12 @@ static char *make_driver_name(struct device_driver *drv) static void module_create_drivers_dir(struct module_kobject *mk) { - if (!mk || mk->drivers_dir) - return; + static DEFINE_MUTEX(drivers_dir_mutex); - mk->drivers_dir = kobject_create_and_add("drivers", &mk->kobj); + mutex_lock(&drivers_dir_mutex); + if (mk && !mk->drivers_dir) + mk->drivers_dir = kobject_create_and_add("drivers", &mk->kobj); + mutex_unlock(&drivers_dir_mutex); } void module_add_driver(struct module *mod, struct device_driver *drv)