On 02/27, Will Drewry wrote:

On Mon, Feb 27, 2012 at 11:22 AM, Oleg Nesterov [off-list ref] wrote:

quoted

On 02/24, Will Drewry wrote:

quoted

To ensure that SIGSYS delivery occurs on return from the triggering
system call, SIGSYS is added to the SYNCHRONOUS_MASK macro.

Hmm. Can't understand... please help.

quoted

 #define SYNCHRONOUS_MASK \
      (sigmask(SIGSEGV) | sigmask(SIGBUS) | sigmask(SIGILL) | \
-      sigmask(SIGTRAP) | sigmask(SIGFPE))
+      sigmask(SIGTRAP) | sigmask(SIGFPE) | sigmask(SIGSYS))

Why?

SYNCHRONOUS_MASK just tells dequeue_signal() "pick them first".
This is needed to make sure that the handler for, say SIGSEGV,
can use ucontext->ip as a faulting addr.

I think that Roland covered this.  (Since the syscall_rollback was
called it's nice to let our handler get first go.)

OK, except I do not really understand the "our handler get first go".

Suppose SIGSYS "races" with the pending SIGHUP. With this change
the caller for SIGHUP will be called first. But yes, setup_frame()
will be called for SIGSYS first. Hopefully this is what you want.

quoted

But seccomp adds info->si_call_addr, this looks unneeded.

True enough.  I can drop it.

Hmm. I meant, the change in SYNCHRONOUS_MASK looks unneeded. Please
keep ->si_call_addr, it is much more convenient than ucontext_t in
userspace.

It'd only be useful if the SIGSYS wasn't
being forced and the signal was being handled without ucontext_t
access.

No, force_ doesn't make any difference in this sense...

In short, the patch looks fine to me, but if you resend it may be
you can update the changelog.

Oleg.