s390: clear pt_regs::flags on irq entry

The current irq entry code doesn't initialize pt_regs::flags. On exit to
user mode arch_do_signal_or_restart() tests whether PIF_SYSCALL is set,
which might yield wrong results.

Fix this by clearing pt_regs::flags in the entry.S irq handler
code.

Reported-by: Heiko Carstens <[email protected]>
Signed-off-by: Sven Schnelle <[email protected]>
Reviewed-by: Heiko Carstens <[email protected]>
Fixes: 56e62a7 ("s390: convert to generic entry")
Cc: <[email protected]> # 5.12
Signed-off-by: Vasily Gorbik <[email protected]>

Author: svens-s390

arch/s390/kernel/entry.S

@@ -418,6 +418,7 @@ ENTRY(\name)
 	xgr	%r6,%r6
 	xgr	%r7,%r7
 	xgr	%r10,%r10
+	xc	__PT_FLAGS(8,%r11),__PT_FLAGS(%r11)
 	mvc	__PT_R8(64,%r11),__LC_SAVE_AREA_ASYNC
 	stmg	%r8,%r9,__PT_PSW(%r11)
 	tm	%r8,0x0001		# coming from user space?