whack-a-mole: no need to set_fs(USER_DS) in {start,flush}_thread()

flush_old_exec() has already done that.  Back on 2011 a bunch of
instances like that had been kicked out, but that hadn't taken
care of then-out-of-tree architectures, obviously, and they served
as reinfection vector...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/arc/kernel/process.c

@@ -155,8 +155,6 @@ int copy_thread(unsigned long clone_flags,
  */
 void start_thread(struct pt_regs * regs, unsigned long pc, unsigned long usp)
 {
-	set_fs(USER_DS); /* user space */
-
 	regs->sp = usp;
 	regs->ret = pc;
 

arch/c6x/kernel/process.c

@@ -101,7 +101,6 @@ void start_thread(struct pt_regs *regs, unsigned int pc, unsigned long usp)
 	 */
 	usp -= 8;
 
-	set_fs(USER_DS);
 	regs->pc  = pc;
 	regs->sp  = usp;
 	regs->tsr |= 0x40; /* set user mode */

arch/hexagon/kernel/process.c

@@ -37,8 +37,6 @@
  */
 void start_thread(struct pt_regs *regs, unsigned long pc, unsigned long sp)
 {
-	/* Set to run with user-mode data segmentation */
-	set_fs(USER_DS);
 	/* We want to zero all data-containing registers. Is this overkill? */
 	memset(regs, 0, sizeof(*regs));
 	/* We might want to also zero all Processor registers here */

arch/metag/include/asm/processor.h

@@ -111,7 +111,6 @@ struct thread_struct {
  */
 #define start_thread(regs, pc, usp) do {				   \
 	unsigned int *argc = (unsigned int *) bprm->exec;		   \
-	set_fs(USER_DS);						   \
 	current->thread.int_depth = 1;					   \
 	/* Force this process down to user land */			   \
 	regs->ctx.SaveMask = TBICTX_PRIV_BIT;				   \

arch/nios2/kernel/process.c

@@ -94,7 +94,6 @@ void show_regs(struct pt_regs *regs)
 
 void flush_thread(void)
 {
-	set_fs(USER_DS);
 }
 
 int copy_thread(unsigned long clone_flags,

arch/openrisc/kernel/process.c

@@ -197,7 +197,6 @@ void start_thread(struct pt_regs *regs, unsigned long pc, unsigned long sp)
 {
 	unsigned long sr = mfspr(SPR_SR) & ~SPR_SR_SM;
 
-	set_fs(USER_DS);
 	memset(regs, 0, sizeof(struct pt_regs));
 
 	regs->pc = pc;