* [PATCH] base: make module_create_drivers_dir race-free
@ 2016-06-10 8:54 Jiri Slaby
2016-06-10 16:25 ` Greg KH
0 siblings, 1 reply; 2+ messages in thread
From: Jiri Slaby @ 2016-06-10 8:54 UTC (permalink / raw)
To: gregkh; +Cc: linux-kernel, Jiri Slaby, v2 . 6 . 21+
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:
...
[<ffffffff812e63a2>] sysfs_warn_dup+0x62/0x80
[<ffffffff812e6487>] sysfs_create_dir_ns+0x77/0x90
[<ffffffff8140f2c4>] kobject_add_internal+0xb4/0x340
[<ffffffff8140f5b8>] kobject_add+0x68/0xb0
[<ffffffff8140f631>] kobject_create_and_add+0x31/0x70
[<ffffffff8157a703>] module_add_driver+0xc3/0xd0
[<ffffffff8155e5d4>] bus_add_driver+0x154/0x280
[<ffffffff815604c0>] driver_register+0x60/0xe0
[<ffffffff8145bed0>] __pci_register_driver+0x60/0x70
[<ffffffffa0273e14>] saa7146_register_extension+0x64/0x90 [saa7146]
[<ffffffffa0033011>] 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 <jslaby@suse.cz>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Fixes: fe480a2675ed (Modules: only add drivers/ direcory if needed)
Cc: v2.6.21+ <stable@vger.kernel.org>
---
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)
--
2.8.4
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] base: make module_create_drivers_dir race-free
2016-06-10 8:54 [PATCH] base: make module_create_drivers_dir race-free Jiri Slaby
@ 2016-06-10 16:25 ` Greg KH
0 siblings, 0 replies; 2+ messages in thread
From: Greg KH @ 2016-06-10 16:25 UTC (permalink / raw)
To: Jiri Slaby; +Cc: linux-kernel, v2 . 6 . 21+
On Fri, Jun 10, 2016 at 10:54:32AM +0200, Jiri Slaby wrote:
> 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:
> ...
> [<ffffffff812e63a2>] sysfs_warn_dup+0x62/0x80
> [<ffffffff812e6487>] sysfs_create_dir_ns+0x77/0x90
> [<ffffffff8140f2c4>] kobject_add_internal+0xb4/0x340
> [<ffffffff8140f5b8>] kobject_add+0x68/0xb0
> [<ffffffff8140f631>] kobject_create_and_add+0x31/0x70
> [<ffffffff8157a703>] module_add_driver+0xc3/0xd0
> [<ffffffff8155e5d4>] bus_add_driver+0x154/0x280
> [<ffffffff815604c0>] driver_register+0x60/0xe0
> [<ffffffff8145bed0>] __pci_register_driver+0x60/0x70
> [<ffffffffa0273e14>] saa7146_register_extension+0x64/0x90 [saa7146]
> [<ffffffffa0033011>] 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.
Wow, good catch, I would never have expected that.
I'll go queue this up soon, thanks.
greg k-h
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