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Commit 44fbbb3d authored by Al Viro's avatar Al Viro
Browse files

x86: get rid of calling do_notify_resume() when returning to kernel mode 



If we end up calling do_notify_resume() with !user_mode(refs), it
does nothing (do_signal() explicitly bails out and we can't get there
with TIF_NOTIFY_RESUME in such situations).  Then we jump to
resume_userspace_sig, which rechecks the same thing and bails out
to resume_kernel, thus breaking the loop.

It's easier and cheaper to check *before* calling do_notify_resume()
and bail out to resume_kernel immediately.  And kill the check in
do_signal()...

Note that on amd64 we can't get there with !user_mode() at all - asm
glue takes care of that.

Acked-and-reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 29bf5dd8

arch/x86/kernel/entry_32.S

+10 −3
Original line number Diff line number Diff line
@@ -316,7 +316,6 @@ ret_from_exception: 
	preempt_stop(CLBR_ANY)

ret_from_intr:

	GET_THREAD_INFO(%ebp)

resume_userspace_sig:

#ifdef CONFIG_VM86

	movl PT_EFLAGS(%esp), %eax	# mix EFLAGS and CS

	movb PT_CS(%esp), %al
@@ -615,9 +614,13 @@ work_notifysig: # deal with pending signals and 
					# vm86-space

	TRACE_IRQS_ON

	ENABLE_INTERRUPTS(CLBR_NONE)

	movb PT_CS(%esp), %bl

	andb $SEGMENT_RPL_MASK, %bl

	cmpb $USER_RPL, %bl

	jb resume_kernel

	xorl %edx, %edx

	call do_notify_resume

	jmp resume_userspace_sig

	jmp resume_userspace



	ALIGN

work_notifysig_v86:
@@ -630,9 +633,13 @@ work_notifysig_v86: 
#endif

	TRACE_IRQS_ON

	ENABLE_INTERRUPTS(CLBR_NONE)

	movb PT_CS(%esp), %bl

	andb $SEGMENT_RPL_MASK, %bl

	cmpb $USER_RPL, %bl

	jb resume_kernel

	xorl %edx, %edx

	call do_notify_resume

	jmp resume_userspace_sig

	jmp resume_userspace

END(work_pending)



	# perform syscall exit tracing

arch/x86/kernel/signal.c

+0 −10
Original line number Diff line number Diff line
@@ -737,16 +737,6 @@ static void do_signal(struct pt_regs *regs) 
	siginfo_t info;

	int signr;



	/*

	 * We want the common case to go fast, which is why we may in certain

	 * cases get here from kernel mode. Just return without doing anything

	 * if so.

	 * X86_32: vm86 regs switched out by assembly code before reaching

	 * here, so testing against kernel CS suffices.

	 */

	if (!user_mode(regs))

		return;



	signr = get_signal_to_deliver(&info, &ka, regs, NULL);

	if (signr > 0) {

		/* Whee! Actually deliver the signal.  */