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[PATCH 3.2 53/94] base: make module_create_drivers_dir race-free

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3.2.82-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jiri Slaby <jslaby@suse.cz>

commit 7e1b1fc4dabd6ec8e28baa0708866e13fa93c9b3 upstream.

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>
Fixes: fe480a2675ed (Modules: only add drivers/ direcory if needed)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 drivers/base/module.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/base/module.c
+++ b/drivers/base/module.c
@@ -24,10 +24,12 @@ static char *make_driver_name(struct dev
 
 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)

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[PATCH 3.2 00/94] 3.2.82-rc1 review Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 13:50 +0200
  [PATCH 3.2 26/94] fs/cifs: correctly to anonymous authentication  for the LANMAN authentication Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 13:50 +0200
  [PATCH 3.2 23/94] x86/PCI: Mark Broadwell-EP Home Agent 1 as  having non-compliant BARs Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 13:50 +0200
  [PATCH 3.2 93/94] tcp: make challenge acks less predictable Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 13:50 +0200
  [PATCH 3.2 62/94] UBIFS: Implement ->migratepage() Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 42/94] x86, build: copy ldlinux.c32 to image.iso Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 54/94] kvm: Fix irq route entries exceeding  KVM_MAX_IRQ_ROUTES Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 13/94] USB: serial: option: add even more ZTE device ids Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 35/94] Input: xpad - prevent spurious input from wired  Xbox 360 controllers Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 43/94] fix d_walk()/non-delayed __d_free() race Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 18/94] powerpc/mm/hash64: Factor out hash preload  psize check Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:00 +0200
  [PATCH 3.2 86/94] proc: prevent stacking filesystems on top Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 34/94] RDMA/cxgb3: device driver frees DMA memory with  different size Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 22/94] net/mlx4_core: Fix access to uninitialized index Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 82/94] xenbus: don't BUG() on user mode induced condition Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 69/94] ALSA: dummy: Fix a use-after-free at closing Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 74/94] NFS: Fix another OPEN_DOWNGRADE bug Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 73/94] ALSA: echoaudio: Fix memory allocation Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 61/94] mm: Export migrate_page_move_mapping and  migrate_page_copy Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  [PATCH 3.2 02/94] ath5k: Change led pin configuration for compaq  c700 laptop Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 14:10 +0200
  Re: [PATCH 3.2 00/94] 3.2.82-rc1 review Guenter Roeck <linux@roeck-us.net> - 2016-08-14 17:10 +0200
  [PATCH 3.2 39/94] ARM: fix PTRACE_SETVFPREGS on SMP systems Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 85/94] fs: limit filesystem stacking depth Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 11/94] tty: vt, return error when con_startup fails Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 91/94] tipc: fix an infoleak in tipc_nl_compat_link_dump Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 15/94] MIPS: Adjust set_pte() SMP fix to handle  R10000_LLSC_WAR Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 60/94] ubi: Make recover_peb power cut aware Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 03/94] crypto: s5p-sss - Fix missed interrupts when  working with 8 kB blocks Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 64/94] xen/pciback: Fix conf_space read/write overlap  check. Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 25/94] fs/cifs: correctly to anonymous authentication  via NTLMSSP Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:00 +0200
  [PATCH 3.2 37/94] Input: pwm-beeper - fix - scheduling while atomic Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 21/94] mmc: mmc: Fix partition switch timeout for some  eMMCs Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 88/94] ALSA: timer: Fix leak in SNDRV_TIMER_IOCTL_PARAMS Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 01/94] regmap: cache: Fix typo in cache_bypass  parameter description Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 63/94] can: fix oops caused by wrong rtnl dellink usage Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 77/94] x86/amd_nb: Fix boot crash on non-AMD systems Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 79/94] bonding: prevent out of bound accesses Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 06/94] crypto: s5p-sss - fix incorrect usage of  scatterlists api Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 59/94] can: at91_can: RX queue could get stuck at high  bus load Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 70/94] fs/nilfs2: fix potential underflow in call to  crc32_le Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 71/94] staging: iio: accel: fix error check Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 84/94] cifs: dynamic allocation of ntlmssp blob Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 52/94] kernel/sysrq, watchdog, sched/core: Reset  watchdog on all CPUs while processing sysrq-w Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 40/94] KVM: x86: fix OOPS after invalid KVM_SET_DEBUGREGS Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 53/94] base: make module_create_drivers_dir race-free Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:10 +0200
  [PATCH 3.2 87/94] USB: usbfs: fix potential infoleak in devio Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:20 +0200
  [PATCH 3.2 48/94] staging:iio: trigger fixes for repeat request  of same trigger and allocation failure Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:20 +0200
  [PATCH 3.2 09/94] ext4: fix hang when processing corrupted  orphaned inode list Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:20 +0200
  [PATCH 3.2 75/94] batman-adv: Fix use-after-free/double-free of  tt_req_node Ben Hutchings <ben@decadent.org.uk> - 2016-08-14 20:20 +0200

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