Messages in this thread | | | Date | Mon, 1 Aug 2022 15:36:32 +0200 | From | "Jason A. Donenfeld" <> | Subject | Re: [PATCH v4] lib/vsprintf: defer filling siphash key on RT |
| |
Hi Sebastian,
On Mon, Aug 01, 2022 at 02:46:35PM +0200, Sebastian Andrzej Siewior wrote: > On 2022-08-01 14:39:46 [+0200], Jason A. Donenfeld wrote: > > On RT, we can't call get_random_bytes() from inside of the raw locks > > that callers of vsprintf might take, because get_random_bytes() takes > > normal spinlocks. So on those RT systems, defer the siphash key > > generation to a worker. > > > > Also, avoid using a static_branch, as this isn't the fast path. > > Using static_branch_likely() to signal that ptr_key has been filled is a > > bit much given that it is not a fast path. > > > > Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > > Reported-by: Mike Galbraith <efault@gmx.de> > > Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> > > --- > > Sebastian - feel free to take this and tweak it as needed. Sending this > > mostly as something illustrative of what the "simpler" thing would be > > that I had in mind. -Jason > > Can have the same behaviour regardless of CONFIG_PREEMPT_RT? Here > lockdep _may_ yell with !RT because it is broken for RT. > If we agree that we drop the first %p print here, can we do this on > both (regardless of CONFIG_PREEMPT_RT)?
"Lockdep may yell" -- but this would be when lockdep is turned on to catch RT bugs, not to catch non-RT bugs. The actual bug only exists on RT. This is an RT problem. Stop pretending that this is a real issue outside of RT. It isn't. This is *only* an RT issue. So why would we make things worse for an issue that doesn't actually exist on non-RT?
I too generally prefer having only one code path and not two. But the way this patch is written, the worker function just gets reused with a straight call on the non-RT case, so it doesn't actually require duplicating code.
Jason
| |