fix duart locking

Hi Ralf,

the duart code tries to hold a spin lock across a call to copy_from_user(). This patch releases the spin lock before the call and reacquires it afterwards.

peter

? drivers/i2c/algos/.built-in.o.cmd
? drivers/i2c/algos/.i2c-algo-bit.o.cmd
? drivers/i2c/busses/.built-in.o.cmd
? drivers/i2c/chips/.built-in.o.cmd
? drivers/input/misc/.built-in.o.cmd
? drivers/input/misc/.pcspkr.o.cmd
? drivers/input/misc/.uinput.o.cmd
Index: drivers/char/sb1250_duart.c
===================================================================
RCS file: /home/cvs/linux/drivers/char/sb1250_duart.c,v retrieving revision 1.23

diff -u -r1.23 sb1250_duart.c
@@ -326,10 +326,11 @@
 		if (c <= 0) break;
 
 		if (from_user) {
+			spin_unlock_irqrestore(&us->outp_lock, flags);
 			if (copy_from_user(us->outp_buf + us->outp_tail, buf, c)) {
-				spin_unlock_irqrestore(&us->outp_lock, flags);
 				return -EFAULT;
 			}
+			spin_lock_irqsave(&us->outp_lock, flags);
 		} else {
 			memcpy(us->outp_buf + us->outp_tail, buf, c);
 		}