RE: [PATCH v1 3/5] mm, uaccess: trigger might_sleep() in might_fault() when pagefaults are disabled

From: David Laight
Date: Fri Dec 05 2014 - 07:09:10 EST

From: David Hildenbrand [...
> > This should be likely() instead of unlikely(), no?
> > I'd rather write this
> >
> > if (pagefault_disabled())
> > return;
> > __might_sleep(file, line, 0);
> >
> > and leave the likely stuff completely away.
> Makes perfect sense!

>From my experience of getting (an older version of) gcc to emit
'correctly' statically predicted branches I found that code that
looks like (I don't think return/goto make any difference):

If (unlikely(condition)) {

is compile with a forwards conditional branch (ie ignoring the unlikely()).
Similarly 'if () continue' is likely to generate a 'predicted taken'
backwards conditional branch.

To get the desired effect you need a non-empty 'else' part, an assembler
comment will suffice, eg: asm volatile("# comment").


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at