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authorJarod Wilson <jarod@redhat.com>2011-04-27 19:01:44 -0300
committerGreg Kroah-Hartman <gregkh@suse.de>2011-05-09 15:06:43 -0700
commita9e7fb583786f69426aae4e569f16c8d34b6bdf5 (patch)
tree48c5b8fac71a6f7414b2fc55e2c5dc2d9a54df25 /drivers
parent658bdc683c81e8016a6be9e3d0c1e5aa139a9b5d (diff)
downloadlinux-2.6.38-lt-ux500-a9e7fb583786f69426aae4e569f16c8d34b6bdf5.tar.gz
imon: add conditional locking in change_protocol
commit 23ef710e1a6c4d6b9ef1c2fa19410f7f1479401e upstream. The imon_ir_change_protocol function gets called two different ways, one way is from rc_register_device, for initial protocol selection/setup, and the other is via a userspace-initiated protocol change request, either by direct sysfs prodding or by something like ir-keytable. In the rc_register_device case, the imon context lock is already held, but when initiated from userspace, it is not, so we must acquire it, prior to calling send_packet, which requires that the lock is held. Without this change, there's an easily reproduceable deadlock when another function calls send_packet (such as either of the display write fops) after a userspace-initiated change_protocol. With a lock-debugging-enabled kernel, I was getting this: [ 15.014153] ===================================== [ 15.015048] [ BUG: bad unlock balance detected! ] [ 15.015048] ------------------------------------- [ 15.015048] ir-keytable/773 is trying to release lock (&ictx->lock) at: [ 15.015048] [<ffffffff814c6297>] mutex_unlock+0xe/0x10 [ 15.015048] but there are no more locks to release! [ 15.015048] [ 15.015048] other info that might help us debug this: [ 15.015048] 2 locks held by ir-keytable/773: [ 15.015048] #0: (&buffer->mutex){+.+.+.}, at: [<ffffffff8119d400>] sysfs_write_file+0x3c/0x144 [ 15.015048] #1: (s_active#87){.+.+.+}, at: [<ffffffff8119d4ab>] sysfs_write_file+0xe7/0x144 [ 15.015048] [ 15.015048] stack backtrace: [ 15.015048] Pid: 773, comm: ir-keytable Not tainted 2.6.38.4-20.fc15.x86_64.debug #1 [ 15.015048] Call Trace: [ 15.015048] [<ffffffff81089715>] ? print_unlock_inbalance_bug+0xca/0xd5 [ 15.015048] [<ffffffff8108b35c>] ? lock_release_non_nested+0xc1/0x263 [ 15.015048] [<ffffffff814c6297>] ? mutex_unlock+0xe/0x10 [ 15.015048] [<ffffffff814c6297>] ? mutex_unlock+0xe/0x10 [ 15.015048] [<ffffffff8108b67b>] ? lock_release+0x17d/0x1a4 [ 15.015048] [<ffffffff814c6229>] ? __mutex_unlock_slowpath+0xc5/0x125 [ 15.015048] [<ffffffff814c6297>] ? mutex_unlock+0xe/0x10 [ 15.015048] [<ffffffffa02964b6>] ? send_packet+0x1c9/0x264 [imon] [ 15.015048] [<ffffffff8108b376>] ? lock_release_non_nested+0xdb/0x263 [ 15.015048] [<ffffffffa0296731>] ? imon_ir_change_protocol+0x126/0x15e [imon] [ 15.015048] [<ffffffffa024a334>] ? store_protocols+0x1c3/0x286 [rc_core] [ 15.015048] [<ffffffff81326e4e>] ? dev_attr_store+0x20/0x22 [ 15.015048] [<ffffffff8119d4cc>] ? sysfs_write_file+0x108/0x144 ... The original report that led to the investigation was the following: [ 1679.457305] INFO: task LCDd:8460 blocked for more than 120 seconds. [ 1679.457307] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 1679.457309] LCDd D ffff88010fcd89c8 0 8460 1 0x00000000 [ 1679.457312] ffff8800d5a03b48 0000000000000082 0000000000000000 ffff8800d5a03fd8 [ 1679.457314] 00000000012dcd30 fffffffffffffffd ffff8800d5a03fd8 ffff88010fcd86f0 [ 1679.457316] ffff8800d5a03fd8 ffff8800d5a03fd8 ffff88010fcd89d0 ffff8800d5a03fd8 [ 1679.457319] Call Trace: [ 1679.457324] [<ffffffff810ff1a5>] ? zone_statistics+0x75/0x90 [ 1679.457327] [<ffffffff810ea907>] ? get_page_from_freelist+0x3c7/0x820 [ 1679.457330] [<ffffffff813b0a49>] __mutex_lock_slowpath+0x139/0x320 [ 1679.457335] [<ffffffff813b0c41>] mutex_lock+0x11/0x30 [ 1679.457338] [<ffffffffa0d54216>] display_open+0x66/0x130 [imon] [ 1679.457345] [<ffffffffa01d06c0>] usb_open+0x180/0x310 [usbcore] [ 1679.457349] [<ffffffff81143b3b>] chrdev_open+0x1bb/0x2d0 [ 1679.457350] [<ffffffff8113d93d>] __dentry_open+0x10d/0x370 [ 1679.457352] [<ffffffff81143980>] ? chrdev_open+0x0/0x2d0 ... Bump the driver version here so its easier to tell if people have this locking fix or not, and also make locking during probe easier to follow. Reported-by: Benjamin Hodgetts <ben@xnode.org> Signed-off-by: Jarod Wilson <jarod@redhat.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/media/rc/imon.c31
1 files changed, 27 insertions, 4 deletions
diff --git a/drivers/media/rc/imon.c b/drivers/media/rc/imon.c
index e7dc6b46fdf..eee39570f23 100644
--- a/drivers/media/rc/imon.c
+++ b/drivers/media/rc/imon.c
@@ -46,7 +46,7 @@
#define MOD_AUTHOR "Jarod Wilson <jarod@wilsonet.com>"
#define MOD_DESC "Driver for SoundGraph iMON MultiMedia IR/Display"
#define MOD_NAME "imon"
-#define MOD_VERSION "0.9.2"
+#define MOD_VERSION "0.9.3"
#define DISPLAY_MINOR_BASE 144
#define DEVICE_NAME "lcd%d"
@@ -451,8 +451,9 @@ static int display_close(struct inode *inode, struct file *file)
}
/**
- * Sends a packet to the device -- this function must be called
- * with ictx->lock held.
+ * Sends a packet to the device -- this function must be called with
+ * ictx->lock held, or its unlock/lock sequence while waiting for tx
+ * to complete can/will lead to a deadlock.
*/
static int send_packet(struct imon_context *ictx)
{
@@ -982,12 +983,21 @@ static void imon_touch_display_timeout(unsigned long data)
* the iMON remotes, and those used by the Windows MCE remotes (which is
* really just RC-6), but only one or the other at a time, as the signals
* are decoded onboard the receiver.
+ *
+ * This function gets called two different ways, one way is from
+ * rc_register_device, for initial protocol selection/setup, and the other is
+ * via a userspace-initiated protocol change request, either by direct sysfs
+ * prodding or by something like ir-keytable. In the rc_register_device case,
+ * the imon context lock is already held, but when initiated from userspace,
+ * it is not, so we must acquire it prior to calling send_packet, which
+ * requires that the lock is held.
*/
static int imon_ir_change_protocol(struct rc_dev *rc, u64 rc_type)
{
int retval;
struct imon_context *ictx = rc->priv;
struct device *dev = ictx->dev;
+ bool unlock = false;
unsigned char ir_proto_packet[] = {
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x86 };
@@ -1020,6 +1030,11 @@ static int imon_ir_change_protocol(struct rc_dev *rc, u64 rc_type)
memcpy(ictx->usb_tx_buf, &ir_proto_packet, sizeof(ir_proto_packet));
+ if (!mutex_is_locked(&ictx->lock)) {
+ unlock = true;
+ mutex_lock(&ictx->lock);
+ }
+
retval = send_packet(ictx);
if (retval)
goto out;
@@ -1028,6 +1043,9 @@ static int imon_ir_change_protocol(struct rc_dev *rc, u64 rc_type)
ictx->pad_mouse = false;
out:
+ if (unlock)
+ mutex_unlock(&ictx->lock);
+
return retval;
}
@@ -2125,6 +2143,7 @@ static struct imon_context *imon_init_intf0(struct usb_interface *intf)
goto rdev_setup_failed;
}
+ mutex_unlock(&ictx->lock);
return ictx;
rdev_setup_failed:
@@ -2196,6 +2215,7 @@ static struct imon_context *imon_init_intf1(struct usb_interface *intf,
goto urb_submit_failed;
}
+ mutex_unlock(&ictx->lock);
return ictx;
urb_submit_failed:
@@ -2290,6 +2310,8 @@ static int __devinit imon_probe(struct usb_interface *interface,
usb_set_intfdata(interface, ictx);
if (ifnum == 0) {
+ mutex_lock(&ictx->lock);
+
if (product == 0xffdc && ictx->rf_device) {
sysfs_err = sysfs_create_group(&interface->dev.kobj,
&imon_rf_attr_group);
@@ -2300,13 +2322,14 @@ static int __devinit imon_probe(struct usb_interface *interface,
if (ictx->display_supported)
imon_init_display(ictx, interface);
+
+ mutex_unlock(&ictx->lock);
}
dev_info(dev, "iMON device (%04x:%04x, intf%d) on "
"usb<%d:%d> initialized\n", vendor, product, ifnum,
usbdev->bus->busnum, usbdev->devnum);
- mutex_unlock(&ictx->lock);
mutex_unlock(&driver_lock);
return 0;