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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: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2012-04-30 18:24:46 -04:00
parent 29bf5dd895
commit 44fbbb3dc6
2 changed files with 10 additions and 13 deletions
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13
arch/x86/kernel/entry_32.S
View File

@ -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

10
arch/x86/kernel/signal.c
View File

@ -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. */