This is a note to let you know that I've just added the patch titled
base: make module_create_drivers_dir race-free
to my driver-core git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core.git
in the driver-core-linus branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.
If you have any questions about this process, please let me know.
>From 7e1b1fc4dabd6ec8e28baa0708866e13fa93c9b3 Mon Sep 17 00:00:00 2001
From: Jiri Slaby <jslaby@xxxxxxx>
Date: Fri, 10 Jun 2016 10:54:32 +0200
Subject: 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:
...
[<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@xxxxxxx>
Fixes: fe480a2675ed (Modules: only add drivers/ direcory if needed)
Cc: v2.6.21+ <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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)
--
2.8.3
--
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