• Jiri Slaby's avatar
    base: make module_create_drivers_dir race-free · 7e1b1fc4
    Jiri Slaby authored
    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: default avatarJiri Slaby <jslaby@suse.cz>
    Fixes: fe480a26 (Modules: only add drivers/ direcory if needed)
    Cc: v2.6.21+ <stable@vger.kernel.org>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    7e1b1fc4