[PATCH][v2] x86/process: Return early if TIF_IO_BITMAP is set but no IO bitmap is assigned

[lirongqing <lirongqing@baidu.com>]

From: Li RongQing <lirongqing@baidu.com>

Outside the IOPL emulation path, the IO bitmap is always expected
to be allocated when TIF_IO_BITMAP is set. The paranoid WARN_ON_ONCE()
handles the case where the flag and the pointer got out of sync.
In this rare scenario, return early instead of continuing and
dereferencing a NULL pointer.

[Sohil Mehta: rephrased commit message]

Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
---
Diff with v1: rephrased commit message

 arch/x86/kernel/process.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 4c718f8..d5cd217 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -486,6 +486,7 @@ void native_tss_update_io_bitmap(void)
 		if (WARN_ON_ONCE(!iobm)) {
 			clear_thread_flag(TIF_IO_BITMAP);
 			native_tss_invalidate_io_bitmap();
+			return;
 		}
 
 		/*
-- 
2.9.4