On Wed, 2022-10-12 at 21:29 +0000, David Laight wrote: > From: Joe Perches > > Sent: 12 October 2022 20:17 > > > > On Wed, 2022-10-05 at 23:48 +0200, Jason A. Donenfeld wrote: > > > The prandom_u32() function has been a deprecated inline wrapper around > > > get_random_u32() for several releases now, and compiles down to the > > > exact same code. Replace the deprecated wrapper with a direct call to > > > the real function. > > [] > > > diff --git a/drivers/infiniband/hw/cxgb4/cm.c b/drivers/infiniband/hw/cxgb4/cm.c > > [] > > > @@ -734,7 +734,7 @@ static int send_connect(struct c4iw_ep *ep) > > > &ep->com.remote_addr; > > > int ret; > > > enum chip_type adapter_type = ep->com.dev->rdev.lldi.adapter_type; > > > - u32 isn = (prandom_u32() & ~7UL) - 1; > > > + u32 isn = (get_random_u32() & ~7UL) - 1; > > > > trivia: > > > > There are somewhat odd size mismatches here. > > > > I had to think a tiny bit if random() returned a value from 0 to 7 > > and was promoted to a 64 bit value then truncated to 32 bit. > > > > Perhaps these would be clearer as ~7U and not ~7UL > > That makes no difference - the compiler will generate the same code. True, more or less. It's more a question for the reader. > The real question is WTF is the code doing? True. > The '& ~7u' clears the bottom 3 bits. > The '- 1' then sets the bottom 3 bits and decrements the > (random) high bits. Right. > So is the same as get_random_u32() | 7. True, it's effectively the same as the upper 29 bits are random anyway and the bottom 3 bits are always set. > But I bet the coder had something else in mind. Likely. And it was also likely copy/pasted a few times.
