Ah, I didn't notice this email... On 04/28, Al Viro wrote: > > Actually, it looks like on i386 the loop will be broken by checks in > resume_userspace_sig, Yes, > so the worst thing that might happen would be > a bogus call of tracehook_notify_resume() if it's possible to get there > with TIF_NOTIFY_RESUME for kernel thread. Afaics, the kernel should never have TIF_NOTIFY_RESUME. Except (afaics!) a user-space task with TIF_NOTIFY_RESUME does kernel_thread(), and this flag is copied by setup_thread_stack(). But this should be forbidden and we are going to kill daemonize(), probably it already has no callers. > To be honest, I'd rather check for user_mode() before calling > do_notify_resume() and go away to no_work_pending if it's true. Agreed! I tried to suggest this when 29a2e283 was discussed, but my asm skills are close to zero. > --- a/arch/x86/kernel/entry_32.S > +++ b/arch/x86/kernel/entry_32.S > @@ -321,7 +321,6 @@ 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 > @@ -628,9 +627,13 @@ work_notifysig: # deal with pending signals and > # vm86-space > TRACE_IRQS_ON > ENABLE_INTERRUPTS(CLBR_NONE) > + movb PT_CS(%esp), %bl > + andl $SEGMENT_RPL_MASK, %ebx > + cmpl $USER_RPL, %ebx > + jb resume_kernel > xorl %edx, %edx > call do_notify_resume > - jmp resume_userspace_sig > + jmp resume_userspace > > ALIGN > work_notifysig_v86: > @@ -643,9 +646,13 @@ work_notifysig_v86: > #endif > TRACE_IRQS_ON > ENABLE_INTERRUPTS(CLBR_NONE) > + movb PT_CS(%esp), %bl > + andl $SEGMENT_RPL_MASK, %ebx > + cmpl $USER_RPL, %ebx > + jb resume_kernel > xorl %edx, %edx > call do_notify_resume > - jmp resume_userspace_sig > + jmp resume_userspace > END(work_pending) > > # perform syscall exit tracing > diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c > index 595969f..c4aa7c5 100644 > --- a/arch/x86/kernel/signal.c > +++ b/arch/x86/kernel/signal.c > @@ -738,16 +738,6 @@ 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; > - Can't review, but like very much ;) Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
